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| author |   Hou Wenlong <houwenlong.hwl@antgroup.com> | 2022-02-08 17:34:04 +0800 |
|---|---|---|
| committer |   Paolo Bonzini <pbonzini@redhat.com> | 2022-03-01 08:50:49 -0500 |
| commit | 31c66dabaa8a48792469cd2d19a000a0b630aab4 (patch) | |
| tree | 27a8c0f3b620f8bcf2e5012164cfab6327061a03 /arch/x86/kvm/emulate.c | |
| parent | KVM: x86/emulator: Defer not-present segment check in __load_segment_descriptor() (diff) | |
| download | linux-dev-31c66dabaa8a48792469cd2d19a000a0b630aab4.tar.xz linux-dev-31c66dabaa8a48792469cd2d19a000a0b630aab4.zip | |
KVM: x86/emulator: Fix wrong privilege check for code segment in __load_segment_descriptor()
Code segment descriptor can be loaded by jmp/call/ret, iret
and int. The privilege checks are different between those
instructions above realmode. Although, the emulator has
use x86_transfer_type enumerate to differentiate them, but
it is not really used in __load_segment_descriptor(). Note,
far jump/call to call gate, task gate or task state segment
are not implemented in emulator.
As for far jump/call to code segment, if DPL > CPL for conforming
code or (RPL > CPL or DPL != CPL) for non-conforming code, it
should trigger #GP. The current checks are ok.
As for far return, if RPL < CPL or DPL > RPL for conforming
code or DPL != RPL for non-conforming code, it should trigger #GP.
Outer level return is not implemented above virtual-8086 mode in
emulator. So it implies that RPL <= CPL, but the current checks
wouldn't trigger #GP if RPL < CPL.
As for code segment loading in task switch, if DPL > RPL for conforming
code or DPL != RPL for non-conforming code, it should trigger #TS. Since
segment selector is loaded before segment descriptor when load state from
tss, it implies that RPL = CPL, so the current checks are ok.
The only problem in current implementation is missing RPL < CPL check for
far return. However, change code to follow the manual is better.
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Message-Id: <e01f5ea70fc1f18f23da1182acdbc5c97c0e5886.1644292363.git.houwenlong.hwl@antgroup.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/emulate.c')
| -rw-r--r-- | arch/x86/kvm/emulate.c | 31 |
1 files changed, 23 insertions, 8 deletions
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index a6c54b8fdbc7..35e69c2adec2 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1623,14 +1623,29 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt, if (!(seg_desc.type & 8)) goto exception; - if (seg_desc.type & 4) { - /* conforming */ - if (dpl > cpl) - goto exception; - } else { - /* nonconforming */ - if (rpl > cpl || dpl != cpl) - goto exception; + /* RET can never return to an inner privilege level. */ + if (transfer == X86_TRANSFER_RET && rpl < cpl) + goto exception; + if (transfer == X86_TRANSFER_RET || transfer == X86_TRANSFER_TASK_SWITCH) { + if (seg_desc.type & 4) { + /* conforming */ + if (dpl > rpl) + goto exception; + } else { + /* nonconforming */ + if (dpl != rpl) + goto exception; + } + } else { /* X86_TRANSFER_CALL_JMP */ + if (seg_desc.type & 4) { + /* conforming */ + if (dpl > cpl) + goto exception; + } else { + /* nonconforming */ + if (rpl > cpl || dpl != cpl) + goto exception; + } } /* in long-mode d/b must be clear if l is set */ if (seg_desc.d && seg_desc.l) { |