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2020-05-08KVM: x86, SVM: isolate vcpu->arch.dr6 from vmcb->save.dr6Paolo Bonzini5-30/+32
There are two issues with KVM_EXIT_DEBUG on AMD, whose root cause is the different handling of DR6 on intercepted #DB exceptions on Intel and AMD. On Intel, #DB exceptions transmit the DR6 value via the exit qualification field of the VMCS, and the exit qualification only contains the description of the precise event that caused a vmexit. On AMD, instead the DR6 field of the VMCB is filled in as if the #DB exception was to be injected into the guest. This has two effects when guest debugging is in use: * the guest DR6 is clobbered * the kvm_run->debug.arch.dr6 field can accumulate more debug events, rather than just the last one that happened (the testcase in the next patch covers this issue). This patch fixes both issues by emulating, so to speak, the Intel behavior on AMD processors. The important observation is that (after the previous patches) the VMCB value of DR6 is only ever observable from the guest is KVM_DEBUGREG_WONT_EXIT is set. Therefore we can actually set vmcb->save.dr6 to any value we want as long as KVM_DEBUGREG_WONT_EXIT is clear, which it will be if guest debugging is enabled. Therefore it is possible to enter the guest with an all-zero DR6, reconstruct the #DB payload from the DR6 we get at exit time, and let kvm_deliver_exception_payload move the newly set bits into vcpu->arch.dr6. Some extra bits may be included in the payload if KVM_DEBUGREG_WONT_EXIT is set, but this is harmless. This may not be the most optimized way to deal with this, but it is simple and, being confined within SVM code, it gets rid of the set_dr6 callback and kvm_update_dr6. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-08KVM: SVM: keep DR6 synchronized with vcpu->arch.dr6Paolo Bonzini5-28/+21
kvm_x86_ops.set_dr6 is only ever called with vcpu->arch.dr6 as the second argument. Ensure that the VMCB value is synchronized to vcpu->arch.dr6 on #DB (both "normal" and nested) and nested vmentry, so that the current value of DR6 is always available in vcpu->arch.dr6. The get_dr6 callback can just access vcpu->arch.dr6 and becomes redundant. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-07KVM: nSVM: trap #DB and #BP to userspace if guest debugging is onPaolo Bonzini1-0/+8
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-07KVM: selftests: Add KVM_SET_GUEST_DEBUG testPeter Xu4-0/+192
Covers fundamental tests for KVM_SET_GUEST_DEBUG. It is very close to the debug test in kvm-unit-test, but doing it from outside the guest. Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20200505205000.188252-4-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-07KVM: X86: Fix single-step with KVM_SET_GUEST_DEBUGPeter Xu1-1/+1
When single-step triggered with KVM_SET_GUEST_DEBUG, we should fill in the pc value with current linear RIP rather than the cached singlestep address. Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20200505205000.188252-3-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-07KVM: X86: Set RTM for DB_VECTOR too for KVM_EXIT_DEBUGPeter Xu1-1/+1
RTM should always been set even with KVM_EXIT_DEBUG on #DB. Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20200505205000.188252-2-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-07KVM: x86: fix DR6 delivery for various cases of #DB injectionPaolo Bonzini3-11/+9
Go through kvm_queue_exception_p so that the payload is correctly delivered through the exit qualification, and add a kvm_update_dr6 call to kvm_deliver_exception_payload that is needed on AMD. Reported-by: Peter Xu <peterx@redhat.com> Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-07KVM: X86: Declare KVM_CAP_SET_GUEST_DEBUG properlyPeter Xu3-0/+3
KVM_CAP_SET_GUEST_DEBUG should be supported for x86 however it's not declared as supported. My wild guess is that userspaces like QEMU are using "#ifdef KVM_CAP_SET_GUEST_DEBUG" to check for the capability instead, but that could be wrong because the compilation host may not be the runtime host. The userspace might still want to keep the old "#ifdef" though to not break the guest debug on old kernels. Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20200505154750.126300-1-peterx@redhat.com> [Do the same for PPC and s390. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-06KVM: selftests: Fix build for evmcs.hPeter Xu2-2/+5
I got this error when building kvm selftests: /usr/bin/ld: /home/xz/git/linux/tools/testing/selftests/kvm/libkvm.a(vmx.o):/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:222: multiple definition of `current_evmcs'; /tmp/cco1G48P.o:/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:222: first defined here /usr/bin/ld: /home/xz/git/linux/tools/testing/selftests/kvm/libkvm.a(vmx.o):/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:223: multiple definition of `current_vp_assist'; /tmp/cco1G48P.o:/home/xz/git/linux/tools/testing/selftests/kvm/include/evmcs.h:223: first defined here I think it's because evmcs.h is included both in a test file and a lib file so the structs have multiple declarations when linking. After all it's not a good habit to declare structs in the header files. Cc: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20200504220607.99627-1-peterx@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-06kvm: x86: Use KVM CPU capabilities to determine CR4 reserved bitsPaolo Bonzini1-15/+5
Using CPUID data can be useful for the processor compatibility check, but that's it. Using it to compute guest-reserved bits can have both false positives (such as LA57 and UMIP which we are already handling) and false negatives: in particular, with this patch we don't allow anymore a KVM guest to set CR4.PKE when CR4.PKE is clear on the host. Fixes: b9dd21e104bc ("KVM: x86: simplify handling of PKRU") Reported-by: Jim Mattson <jmattson@google.com> Tested-by: Jim Mattson <jmattson@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-06KVM: VMX: Explicitly clear RFLAGS.CF and RFLAGS.ZF in VM-Exit RSB pathSean Christopherson1-0/+3
Clear CF and ZF in the VM-Exit path after doing __FILL_RETURN_BUFFER so that KVM doesn't interpret clobbered RFLAGS as a VM-Fail. Filling the RSB has always clobbered RFLAGS, its current incarnation just happens clear CF and ZF in the processs. Relying on the macro to clear CF and ZF is extremely fragile, e.g. commit 089dd8e53126e ("x86/speculation: Change FILL_RETURN_BUFFER to work with objtool") tweaks the loop such that the ZF flag is always set. Reported-by: Qian Cai <cai@lca.pw> Cc: Rick Edgecombe <rick.p.edgecombe@intel.com> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: stable@vger.kernel.org Fixes: f2fde6a5bcfcf ("KVM: VMX: Move RSB stuffing to before the first RET after VM-Exit") Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Message-Id: <20200506035355.2242-1-sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-06docs/virt/kvm: Document configuring and running nested guestsKashyap Chamarthy2-0/+278
This is a rewrite of this[1] Wiki page with further enhancements. The doc also includes a section on debugging problems in nested environments, among other improvements. [1] https://www.linux-kvm.org/page/Nested_Guests Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com> Message-Id: <20200505112839.30534-1-kchamart@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-04kvm: ioapic: Restrict lazy EOI update to edge-triggered interruptsPaolo Bonzini1-5/+5
Commit f458d039db7e ("kvm: ioapic: Lazy update IOAPIC EOI") introduces the following infinite loop: BUG: stack guard page was hit at 000000008f595917 \ (stack is 00000000bdefe5a4..00000000ae2b06f5) kernel stack overflow (double-fault): 0000 [#1] SMP NOPTI RIP: 0010:kvm_set_irq+0x51/0x160 [kvm] Call Trace: irqfd_resampler_ack+0x32/0x90 [kvm] kvm_notify_acked_irq+0x62/0xd0 [kvm] kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm] ioapic_set_irq+0x20e/0x240 [kvm] kvm_ioapic_set_irq+0x5c/0x80 [kvm] kvm_set_irq+0xbb/0x160 [kvm] ? kvm_hv_set_sint+0x20/0x20 [kvm] irqfd_resampler_ack+0x32/0x90 [kvm] kvm_notify_acked_irq+0x62/0xd0 [kvm] kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm] ioapic_set_irq+0x20e/0x240 [kvm] kvm_ioapic_set_irq+0x5c/0x80 [kvm] kvm_set_irq+0xbb/0x160 [kvm] ? kvm_hv_set_sint+0x20/0x20 [kvm] .... The re-entrancy happens because the irq state is the OR of the interrupt state and the resamplefd state. That is, we don't want to show the state as 0 until we've had a chance to set the resamplefd. But if the interrupt has _not_ gone low then ioapic_set_irq is invoked again, causing an infinite loop. This can only happen for a level-triggered interrupt, otherwise irqfd_inject would immediately set the KVM_USERSPACE_IRQ_SOURCE_ID high and then low. Fortunately, in the case of level-triggered interrupts the VMEXIT already happens because TMR is set. Thus, fix the bug by restricting the lazy invocation of the ack notifier to edge-triggered interrupts, the only ones that need it. Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Reported-by: borisvk@bstnet.org Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Link: https://www.spinics.net/lists/kvm/msg213512.html Fixes: f458d039db7e ("kvm: ioapic: Lazy update IOAPIC EOI") Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=207489 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-04KVM: x86: Fixes posted interrupt check for IRQs delivery modesSuravee Suthikulpanit1-2/+2
Current logic incorrectly uses the enum ioapic_irq_destination_types to check the posted interrupt destination types. However, the value was set using APIC_DM_XXX macros, which are left-shifted by 8 bits. Fixes by using the APIC_DM_FIXED and APIC_DM_LOWEST instead. Fixes: (fdcf75621375 'KVM: x86: Disable posted interrupts for non-standard IRQs delivery modes') Cc: Alexander Graf <graf@amazon.com> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Message-Id: <1586239989-58305-1-git-send-email-suravee.suthikulpanit@amd.com> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Tested-by: Maxim Levitsky <mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-04KVM: SVM: fill in kvm_run->debug.arch.dr[67]Paolo Bonzini1-0/+2
The corresponding code was added for VMX in commit 42dbaa5a057 ("KVM: x86: Virtualize debug registers, 2008-12-15) but never for AMD. Fix this. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-04KVM: nVMX: Replace a BUG_ON(1) with BUG() to squash clang warningSean Christopherson1-1/+1
Use BUG() in the impossible-to-hit default case when switching on the scope of INVEPT to squash a warning with clang 11 due to clang treating the BUG_ON() as conditional. >> arch/x86/kvm/vmx/nested.c:5246:3: warning: variable 'roots_to_free' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized] BUG_ON(1); Reported-by: kbuild test robot <lkp@intel.com> Fixes: ce8fe7b77bd8 ("KVM: nVMX: Free only the affected contexts when emulating INVEPT") Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Message-Id: <20200504153506.28898-1-sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-01KVM: arm64: Fix 32bit PC wrap-aroundMarc Zyngier2-2/+13
In the unlikely event that a 32bit vcpu traps into the hypervisor on an instruction that is located right at the end of the 32bit range, the emulation of that instruction is going to increment PC past the 32bit range. This isn't great, as userspace can then observe this value and get a bit confused. Conversly, userspace can do things like (in the context of a 64bit guest that is capable of 32bit EL0) setting PSTATE to AArch64-EL0, set PC to a 64bit value, change PSTATE to AArch32-USR, and observe that PC hasn't been truncated. More confusion. Fix both by: - truncating PC increments for 32bit guests - sanitizing all 32bit regs every time a core reg is changed by userspace, and that PSTATE indicates a 32bit mode. Cc: stable@vger.kernel.org Acked-by: Will Deacon <will@kernel.org> Signed-off-by: Marc Zyngier <maz@kernel.org>
2020-04-30KVM: arm64: vgic-v4: Initialize GICv4.1 even in the absence of a virtual ITSMarc Zyngier2-2/+10
KVM now expects to be able to use HW-accelerated delivery of vSGIs as soon as the guest has enabled thm. Unfortunately, we only initialize the GICv4 context if we have a virtual ITS exposed to the guest. Fix it by always initializing the GICv4.1 context if it is available on the host. Fixes: 2291ff2f2a56 ("KVM: arm64: GICv4.1: Plumb SGI implementation selection in the distributor") Reviewed-by: Zenghui Yu <yuzenghui@huawei.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
2020-04-30KVM: arm64: Save/restore sp_el0 as part of __guest_enterMarc Zyngier2-14/+26
We currently save/restore sp_el0 in C code. This is a bit unsafe, as a lot of the C code expects 'current' to be accessible from there (and the opportunity to run kernel code in HYP is specially great with VHE). Instead, let's move the save/restore of sp_el0 to the assembly code (in __guest_enter), making sure that sp_el0 is correct very early on when we exit the guest, and is preserved as long as possible to its host value when we enter the guest. Reviewed-by: Andrew Jones <drjones@redhat.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
2020-04-30KVM: arm64: Delete duplicated label in invalid_vectorFangrui Song1-1/+0
SYM_CODE_START defines \label , so it is redundant to define \label again. A redefinition at the same place is accepted by GNU as (https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=159fbb6088f17a341bcaaac960623cab881b4981) but rejected by the clang integrated assembler. Fixes: 617a2f392c92 ("arm64: kvm: Annotate assembly using modern annoations") Signed-off-by: Fangrui Song <maskray@google.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Link: https://github.com/ClangBuiltLinux/linux/issues/988 Link: https://lore.kernel.org/r/20200413231016.250737-1-maskray@google.com
2020-04-23KVM: arm64: vgic-its: Fix memory leak on the error path of vgic_add_lpi()Zenghui Yu1-2/+9
If we're going to fail out the vgic_add_lpi(), let's make sure the allocated vgic_irq memory is also freed. Though it seems that both cases are unlikely to fail. Signed-off-by: Zenghui Yu <yuzenghui@huawei.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20200414030349.625-3-yuzenghui@huawei.com
2020-04-23KVM: arm64: vgic-v3: Retire all pending LPIs on vcpu destroyZenghui Yu1-2/+8
It's likely that the vcpu fails to handle all virtual interrupts if userspace decides to destroy it, leaving the pending ones stay in the ap_list. If the un-handled one is a LPI, its vgic_irq structure will be eventually leaked because of an extra refcount increment in vgic_queue_irq_unlock(). This was detected by kmemleak on almost every guest destroy, the backtrace is as follows: unreferenced object 0xffff80725aed5500 (size 128): comm "CPU 5/KVM", pid 40711, jiffies 4298024754 (age 166366.512s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 08 01 a9 73 6d 80 ff ff ...........sm... c8 61 ee a9 00 20 ff ff 28 1e 55 81 6c 80 ff ff .a... ..(.U.l... backtrace: [<000000004bcaa122>] kmem_cache_alloc_trace+0x2dc/0x418 [<0000000069c7dabb>] vgic_add_lpi+0x88/0x418 [<00000000bfefd5c5>] vgic_its_cmd_handle_mapi+0x4dc/0x588 [<00000000cf993975>] vgic_its_process_commands.part.5+0x484/0x1198 [<000000004bd3f8e3>] vgic_its_process_commands+0x50/0x80 [<00000000b9a65b2b>] vgic_mmio_write_its_cwriter+0xac/0x108 [<0000000009641ebb>] dispatch_mmio_write+0xd0/0x188 [<000000008f79d288>] __kvm_io_bus_write+0x134/0x240 [<00000000882f39ac>] kvm_io_bus_write+0xe0/0x150 [<0000000078197602>] io_mem_abort+0x484/0x7b8 [<0000000060954e3c>] kvm_handle_guest_abort+0x4cc/0xa58 [<00000000e0d0cd65>] handle_exit+0x24c/0x770 [<00000000b44a7fad>] kvm_arch_vcpu_ioctl_run+0x460/0x1988 [<0000000025fb897c>] kvm_vcpu_ioctl+0x4f8/0xee0 [<000000003271e317>] do_vfs_ioctl+0x160/0xcd8 [<00000000e7f39607>] ksys_ioctl+0x98/0xd8 Fix it by retiring all pending LPIs in the ap_list on the destroy path. p.s. I can also reproduce it on a normal guest shutdown. It is because userspace still send LPIs to vcpu (through KVM_SIGNAL_MSI ioctl) while the guest is being shutdown and unable to handle it. A little strange though and haven't dig further... Reviewed-by: James Morse <james.morse@arm.com> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com> [maz: moved the distributor deallocation down to avoid an UAF splat] Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20200414030349.625-2-yuzenghui@huawei.com
2020-04-23KVM: arm: vgic-v2: Only use the virtual state when userspace accesses pending bitsMarc Zyngier3-24/+76
There is no point in accessing the HW when writing to any of the ISPENDR/ICPENDR registers from userspace, as only the guest should be allowed to change the HW state. Introduce new userspace-specific accessors that deal solely with the virtual state. Note that the API differs from that of GICv3, where userspace exclusively uses ISPENDR to set the state. Too bad we can't reuse it. Fixes: 82e40f558de56 ("KVM: arm/arm64: vgic-v2: Handle SGI bits in GICD_I{S,C}PENDR0 as WI") Reviewed-by: James Morse <james.morse@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
2020-04-22KVM: arm: vgic: Only use the virtual state when userspace accesses enable bitsMarc Zyngier4-8/+64
There is no point in accessing the HW when writing to any of the ISENABLER/ICENABLER registers from userspace, as only the guest should be allowed to change the HW state. Introduce new userspace-specific accessors that deal solely with the virtual state. Reported-by: James Morse <james.morse@arm.com> Tested-by: James Morse <james.morse@arm.com> Reviewed-by: James Morse <james.morse@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
2020-04-22KVM: arm: vgic: Synchronize the whole guest on GIC{D,R}_I{S,C}ACTIVER readMarc Zyngier4-44/+75
When a guest tries to read the active state of its interrupts, we currently just return whatever state we have in memory. This means that if such an interrupt lives in a List Register on another CPU, we fail to obsertve the latest active state for this interrupt. In order to remedy this, stop all the other vcpus so that they exit and we can observe the most recent value for the state. This is similar to what we are doing for the write side of the same registers, and results in new MMIO handlers for userspace (which do not need to stop the guest, as it is supposed to be stopped already). Reported-by: Julien Grall <julien@xen.org> Reviewed-by: Andre Przywara <andre.przywara@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org>
2020-04-21KVM: PPC: Book3S HV: Handle non-present PTEs in page fault functionsPaul Mackerras2-8/+10
Since cd758a9b57ee "KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot in HPT page fault handler", it's been possible in fairly rare circumstances to load a non-present PTE in kvmppc_book3s_hv_page_fault() when running a guest on a POWER8 host. Because that case wasn't checked for, we could misinterpret the non-present PTE as being a cache-inhibited PTE. That could mismatch with the corresponding hash PTE, which would cause the function to fail with -EFAULT a little further down. That would propagate up to the KVM_RUN ioctl() generally causing the KVM userspace (usually qemu) to fall over. This addresses the problem by catching that case and returning to the guest instead. For completeness, this fixes the radix page fault handler in the same way. For radix this didn't cause any obvious misbehaviour, because we ended up putting the non-present PTE into the guest's partition-scoped page tables, leading immediately to another hypervisor data/instruction storage interrupt, which would go through the page fault path again and fix things up. Fixes: cd758a9b57ee "KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot in HPT page fault handler" Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1820402 Reported-by: David Gibson <david@gibson.dropbear.id.au> Tested-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
2020-04-20kvm: Disable objtool frame pointer checking for vmenter.SJosh Poimboeuf1-0/+4
Frame pointers are completely broken by vmenter.S because it clobbers RBP: arch/x86/kvm/svm/vmenter.o: warning: objtool: __svm_vcpu_run()+0xe4: BP used as a scratch register That's unavoidable, so just skip checking that file when frame pointers are configured in. On the other hand, ORC can handle that code just fine, so leave objtool enabled in the !FRAME_POINTER case. Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Message-Id: <01fae42917bacad18be8d2cbc771353da6603473.1587398610.git.jpoimboe@redhat.com> Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Fixes: 199cd1d7b534 ("KVM: SVM: Split svm_vcpu_run inline assembly to separate file") Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-04-20MAINTAINERS: add a reviewer for KVM/s390Claudio Imbrenda1-0/+1
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> Acked-by: Cornelia Huck <cohuck@redhat.com> Acked-by: Janosch Frank <frankja@linux.ibm.com> Link: https://lore.kernel.org/r/20200417152936.772256-1-imbrenda@linux.ibm.com
2020-04-20KVM: s390: Fix PV check in deliverable_irqs()Eric Farman1-1/+1
The diag 0x44 handler, which handles a directed yield, goes into a a codepath that does a kvm_for_each_vcpu() and ultimately deliverable_irqs(). The new check for kvm_s390_pv_cpu_is_protected() contains an assertion that the vcpu->mutex is held, which isn't going to be the case in this scenario. The result is a plethora of these messages if the lock debugging is enabled, and thus an implication that we have a problem. WARNING: CPU: 9 PID: 16167 at arch/s390/kvm/kvm-s390.h:239 deliverable_irqs+0x1c6/0x1d0 [kvm] ...snip... Call Trace: [<000003ff80429bf2>] deliverable_irqs+0x1ca/0x1d0 [kvm] ([<000003ff80429b34>] deliverable_irqs+0x10c/0x1d0 [kvm]) [<000003ff8042ba82>] kvm_s390_vcpu_has_irq+0x2a/0xa8 [kvm] [<000003ff804101e2>] kvm_arch_dy_runnable+0x22/0x38 [kvm] [<000003ff80410284>] kvm_vcpu_on_spin+0x8c/0x1d0 [kvm] [<000003ff80436888>] kvm_s390_handle_diag+0x3b0/0x768 [kvm] [<000003ff80425af4>] kvm_handle_sie_intercept+0x1cc/0xcd0 [kvm] [<000003ff80422bb0>] __vcpu_run+0x7b8/0xfd0 [kvm] [<000003ff80423de6>] kvm_arch_vcpu_ioctl_run+0xee/0x3e0 [kvm] [<000003ff8040ccd8>] kvm_vcpu_ioctl+0x2c8/0x8d0 [kvm] [<00000001504ced06>] ksys_ioctl+0xae/0xe8 [<00000001504cedaa>] __s390x_sys_ioctl+0x2a/0x38 [<0000000150cb9034>] system_call+0xd8/0x2d8 2 locks held by CPU 2/KVM/16167: #0: 00000001951980c0 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0x90/0x8d0 [kvm] #1: 000000019599c0f0 (&kvm->srcu){....}, at: __vcpu_run+0x4bc/0xfd0 [kvm] Last Breaking-Event-Address: [<000003ff80429b34>] deliverable_irqs+0x10c/0x1d0 [kvm] irq event stamp: 11967 hardirqs last enabled at (11975): [<00000001502992f2>] console_unlock+0x4ca/0x650 hardirqs last disabled at (11982): [<0000000150298ee8>] console_unlock+0xc0/0x650 softirqs last enabled at (7940): [<0000000150cba6ca>] __do_softirq+0x422/0x4d8 softirqs last disabled at (7929): [<00000001501cd688>] do_softirq_own_stack+0x70/0x80 Considering what's being done here, let's fix this by removing the mutex assertion rather than acquiring the mutex for every other vcpu. Fixes: 201ae986ead7 ("KVM: s390: protvirt: Implement interrupt injection") Signed-off-by: Eric Farman <farman@linux.ibm.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Link: https://lore.kernel.org/r/20200415190353.63625-1-farman@linux.ibm.com Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
2020-04-19Linux 5.7-rc2Linus Torvalds1-1/+1
2020-04-19mm: Fix MREMAP_DONTUNMAP accounting on VMA mergeBrian Geffon1-1/+12
When remapping a mapping where a portion of a VMA is remapped into another portion of the VMA it can cause the VMA to become split. During the copy_vma operation the VMA can actually be remerged if it's an anonymous VMA whose pages have not yet been faulted. This isn't normally a problem because at the end of the remap the original portion is unmapped causing it to become split again. However, MREMAP_DONTUNMAP leaves that original portion in place which means that the VMA which was split and then remerged is not actually split at the end of the mremap. This patch fixes a bug where we don't detect that the VMAs got remerged and we end up putting back VM_ACCOUNT on the next mapping which is completely unreleated. When that next mapping is unmapped it results in incorrectly unaccounting for the memory which was never accounted, and eventually we will underflow on the memory comittment. There is also another issue which is similar, we're currently accouting for the number of pages in the new_vma but that's wrong. We need to account for the length of the remap operation as that's all that is being added. If there was a mapping already at that location its comittment would have been adjusted as part of the munmap at the start of the mremap. A really simple repro can be seen in: https://gist.github.com/bgaff/e101ce99da7d9a8c60acc641d07f312c Fixes: e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Brian Geffon <bgeffon@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-18xattr.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18uapi: linux: fiemap.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18uapi: linux: dlm_device.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-2/+2
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18tpm_eventlog.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-3/+3
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18ti_wilink_st.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-3/+3
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18swap.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18skbuff.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18sched: topology.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18rslib.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18rio.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-2/+2
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18posix_acl.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18platform_data: wilco-ec.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18memcontrol.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-2/+2
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18list_lru.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18lib: cpu_rmap: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18irq.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-2/+2
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18ihex.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18igmp.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18genalloc.h: Replace zero-length array with flexible-array memberGustavo A. R. Silva1-1/+1
The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
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