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| author |   Xiu Jianfeng <xiujianfeng@huawei.com> | 2022-07-01 16:24:35 +0800 |
|---|---|---|
| committer |   Michael Ellerman <mpe@ellerman.id.au> | 2022-07-28 16:22:15 +1000 |
| commit | f4a0318f278d98d9492916722e85f258c2221f88 (patch) | |
| tree | e1526c00daeb382c4e4af213fef62c74c5551796 /arch | |
| parent | powerpc: Move system_call_exception() to syscall.c (diff) | |
| download | linux-dev-f4a0318f278d98d9492916722e85f258c2221f88.tar.xz linux-dev-f4a0318f278d98d9492916722e85f258c2221f88.zip | |
powerpc: add support for syscall stack randomization
Add support for adding a random offset to the stack while handling
syscalls. This patch uses mftb() instead of get_random_int() for better
performance.
In order to avoid unconditional stack canaries on syscall entry (due to
the use of alloca()), also disable stack protector to avoid triggering
needless checks and slowing down the entry path. As there is no general
way to control stack protector coverage with a function attribute, this
must be disabled at the compilation unit level.
Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220701082435.126596-3-xiujianfeng@huawei.com
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/Kconfig | 1 | ||||
| -rw-r--r-- | arch/powerpc/kernel/Makefile | 7 | ||||
| -rw-r--r-- | arch/powerpc/kernel/syscall.c | 19 |
3 files changed, 26 insertions, 1 deletions
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 04499f22d06b..2daeaab21240 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -196,6 +196,7 @@ config PPC select HAVE_ARCH_KASAN if PPC_BOOK3E_64 select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN select HAVE_ARCH_KFENCE if PPC_BOOK3S_32 || PPC_8xx || 40x + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_KGDB select HAVE_ARCH_MMAP_RND_BITS select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile index 0963d39464c8..06d2d1f78f71 100644 --- a/arch/powerpc/kernel/Makefile +++ b/arch/powerpc/kernel/Makefile @@ -54,6 +54,13 @@ CFLAGS_cputable.o += -DDISABLE_BRANCH_PROFILING CFLAGS_btext.o += -DDISABLE_BRANCH_PROFILING endif +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET +# Remove stack protector to avoid triggering unneeded stack canary +# checks due to randomize_kstack_offset. +CFLAGS_REMOVE_syscall.o = -fstack-protector -fstack-protector-strong +CFLAGS_syscall.o += -fno-stack-protector +#endif + obj-y := cputable.o syscalls.o \ irq.o align.o signal_$(BITS).o pmc.o vdso.o \ process.o systbl.o idle.o \ diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c index 4d5689eeaf25..81ace9e8b72b 100644 --- a/arch/powerpc/kernel/syscall.c +++ b/arch/powerpc/kernel/syscall.c @@ -2,6 +2,7 @@ #include <linux/compat.h> #include <linux/context_tracking.h> +#include <linux/randomize_kstack.h> #include <asm/interrupt.h> #include <asm/kup.h> @@ -18,10 +19,12 @@ notrace long system_call_exception(long r3, long r4, long r5, long r6, long r7, long r8, unsigned long r0, struct pt_regs *regs) { + long ret; syscall_fn f; kuap_lock(); + add_random_kstack_offset(); regs->orig_gpr3 = r3; if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG)) @@ -169,5 +172,19 @@ notrace long system_call_exception(long r3, long r4, long r5, f = (void *)sys_call_table[r0]; } - return f(r3, r4, r5, r6, r7, r8); + ret = f(r3, r4, r5, r6, r7, r8); + + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * so the maximum stack offset is 1k bytes (10 bits). + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints: the powerpc architecture + * may have two kinds of stack alignment (16-bytes and 8-bytes). + * + * So the resulting 6 or 7 bits of entropy is seen in SP[9:4] or SP[9:3]. + */ + choose_random_kstack_offset(mftb()); + + return ret; } |