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| author | Sean Christopherson <sean.j.christopherson@intel.com> | 2019-08-23 13:55:44 -0700 |
|---|---|---|
| committer | Radim Krčmář <rkrcmar@redhat.com> | 2019-08-27 20:59:04 +0200 |
| commit | 75ee23b30dc712d80d2421a9a547e7ab6e379b44 (patch) | |
| tree | eb8a7a231a1ab4e740507fe6751ca5ac99148b99 /arch/x86 | |
| parent | ea1529873ab18c204688cf31746df851c098cbea (diff) | |
| download | lwn-75ee23b30dc712d80d2421a9a547e7ab6e379b44.tar.gz lwn-75ee23b30dc712d80d2421a9a547e7ab6e379b44.zip | |
KVM: x86: Don't update RIP or do single-step on faulting emulation
Don't advance RIP or inject a single-step #DB if emulation signals a
fault. This logic applies to all state updates that are conditional on
clean retirement of the emulation instruction, e.g. updating RFLAGS was
previously handled by commit 38827dbd3fb85 ("KVM: x86: Do not update
EFLAGS on faulting emulation").
Not advancing RIP is likely a nop, i.e. ctxt->eip isn't updated with
ctxt->_eip until emulation "retires" anyways. Skipping #DB injection
fixes a bug reported by Andy Lutomirski where a #UD on SYSCALL due to
invalid state with EFLAGS.TF=1 would loop indefinitely due to emulation
overwriting the #UD with #DB and thus restarting the bad SYSCALL over
and over.
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: stable@vger.kernel.org
Reported-by: Andy Lutomirski <luto@kernel.org>
Fixes: 663f4c61b803 ("KVM: x86: handle singlestep during emulation")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/kvm/x86.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 93b0bd45ac73..290c3c3efb87 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6594,12 +6594,13 @@ restart: unsigned long rflags = kvm_x86_ops->get_rflags(vcpu); toggle_interruptibility(vcpu, ctxt->interruptibility); vcpu->arch.emulate_regs_need_sync_to_vcpu = false; - kvm_rip_write(vcpu, ctxt->eip); - if (r == EMULATE_DONE && ctxt->tf) - kvm_vcpu_do_singlestep(vcpu, &r); if (!ctxt->have_exception || - exception_type(ctxt->exception.vector) == EXCPT_TRAP) + exception_type(ctxt->exception.vector) == EXCPT_TRAP) { + kvm_rip_write(vcpu, ctxt->eip); + if (r == EMULATE_DONE && ctxt->tf) + kvm_vcpu_do_singlestep(vcpu, &r); __kvm_set_rflags(vcpu, ctxt->eflags); + } /* * For STI, interrupts are shadowed; so KVM_REQ_EVENT will |