| Message ID | 1621830954-31963-1-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: X86: Fix warning caused by stale emulation context | expand |
On Sun, May 23, 2021, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@tencent.com> > > Reported by syzkaller: > > WARNING: CPU: 7 PID: 10526 at /home/kernel/ssd/linux/arch/x86/kvm//x86.c:7621 x86_emulate_instruction+0x41b/0x510 [kvm] > RIP: 0010:x86_emulate_instruction+0x41b/0x510 [kvm] > Call Trace: > kvm_mmu_page_fault+0x126/0x8f0 [kvm] > vmx_handle_exit+0x11e/0x680 [kvm_intel] > vcpu_enter_guest+0xd95/0x1b40 [kvm] > kvm_arch_vcpu_ioctl_run+0x377/0x6a0 [kvm] > kvm_vcpu_ioctl+0x389/0x630 [kvm] > __x64_sys_ioctl+0x8e/0xd0 > do_syscall_64+0x3c/0xb0 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Commit 4a1e10d5b5d8c (KVM: x86: handle hardware breakpoints during emulation()) > adds hardware breakpoints check before emulation the instruction and parts of > emulation context initialization, actually we don't have EMULTYPE_NO_DECODE flag > here and the emulation context will not be reused. Commit c8848cee74ff (KVM: x86: > set ctxt->have_exception in x86_decode_insn()) triggers the warning because it > catches the stale emulation context has #UD, however, it is not during instruction > decoding which should result in EMULATION_FAILED. This patch fixes it by moving > the second part emulation context initialization before hardware breakpoints check. > > syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134683fdd00000 > > Reported-by: syzbot+71271244f206d17f6441@syzkaller.appspotmail.com > Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation) > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > arch/x86/kvm/x86.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index bbc4e04..eca69f9 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7552,6 +7552,13 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, > > init_emulate_ctxt(vcpu); > > + ctxt->interruptibility = 0; > + ctxt->have_exception = false; > + ctxt->exception.vector = -1; > + ctxt->perm_ok = false; What about moving this block all the way into init_emulate_ctxt()? > + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; This can be left where it is since ctxt->ud is consumed only by x86_decode_insn(). I don't have a strong preference as it really only matters for the backport. For upstream, we can kill it off in a follow-up patch by passing emulation_type to x86_decode_insn() and dropping ctxt->ud altogether. Tracking that info in ctxt for literally one call is silly. diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 8a0ccdb56076..b62944046d7d 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5322,7 +5322,8 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len) ctxt->execute = opcode.u.execute; - if (unlikely(ctxt->ud) && likely(!(ctxt->d & EmulateOnUD))) + if (unlikely(emulation_type & EMULTYPE_TRAP_UD) && + likely(!(ctxt->d & EmulateOnUD))) return EMULATION_FAILED; if (unlikely(ctxt->d & diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h index f016838faedd..2ad32600a8e3 100644 --- a/arch/x86/kvm/kvm_emulate.h +++ b/arch/x86/kvm/kvm_emulate.h @@ -314,7 +314,6 @@ struct x86_emulate_ctxt { int interruptibility; bool perm_ok; /* do not check permissions if true */ - bool ud; /* inject an #UD if host doesn't support insn */ bool tf; /* TF value before instruction (after for syscall/sysret) */ bool have_exception; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a224601d89e2..48b49c24c086 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7552,8 +7552,6 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, init_emulate_ctxt(vcpu); - ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; - /* * We will reenter on the same instruction since we do not set * complete_userspace_io. This does not handle watchpoints yet, @@ -7563,7 +7561,7 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, kvm_vcpu_check_breakpoint(vcpu, &r)) return r; - r = x86_decode_insn(ctxt, insn, insn_len); + r = x86_decode_insn(ctxt, insn, insn_len, emulation_type); trace_kvm_emulate_insn_start(vcpu); ++vcpu->stat.insn_emulation; > + > /* > * We will reenter on the same instruction since we do not set > * complete_userspace_io. This does not handle watchpoints yet, > @@ -7561,13 +7568,6 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, > kvm_vcpu_check_breakpoint(vcpu, &r)) > return r; > > - ctxt->interruptibility = 0; > - ctxt->have_exception = false; > - ctxt->exception.vector = -1; > - ctxt->perm_ok = false; > - > - ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; > - > r = x86_decode_insn(ctxt, insn, insn_len); > > trace_kvm_emulate_insn_start(vcpu); > -- > 2.7.4 >
On Mon, 24 May 2021 at 23:32, Sean Christopherson <seanjc@google.com> wrote: > > On Sun, May 23, 2021, Wanpeng Li wrote: > > From: Wanpeng Li <wanpengli@tencent.com> > > > > Reported by syzkaller: > > > > WARNING: CPU: 7 PID: 10526 at /home/kernel/ssd/linux/arch/x86/kvm//x86.c:7621 x86_emulate_instruction+0x41b/0x510 [kvm] > > RIP: 0010:x86_emulate_instruction+0x41b/0x510 [kvm] > > Call Trace: > > kvm_mmu_page_fault+0x126/0x8f0 [kvm] > > vmx_handle_exit+0x11e/0x680 [kvm_intel] > > vcpu_enter_guest+0xd95/0x1b40 [kvm] > > kvm_arch_vcpu_ioctl_run+0x377/0x6a0 [kvm] > > kvm_vcpu_ioctl+0x389/0x630 [kvm] > > __x64_sys_ioctl+0x8e/0xd0 > > do_syscall_64+0x3c/0xb0 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > Commit 4a1e10d5b5d8c (KVM: x86: handle hardware breakpoints during emulation()) > > adds hardware breakpoints check before emulation the instruction and parts of > > emulation context initialization, actually we don't have EMULTYPE_NO_DECODE flag > > here and the emulation context will not be reused. Commit c8848cee74ff (KVM: x86: > > set ctxt->have_exception in x86_decode_insn()) triggers the warning because it > > catches the stale emulation context has #UD, however, it is not during instruction > > decoding which should result in EMULATION_FAILED. This patch fixes it by moving > > the second part emulation context initialization before hardware breakpoints check. > > > > syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134683fdd00000 > > > > Reported-by: syzbot+71271244f206d17f6441@syzkaller.appspotmail.com > > Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation) > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > > --- > > arch/x86/kvm/x86.c | 14 +++++++------- > > 1 file changed, 7 insertions(+), 7 deletions(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index bbc4e04..eca69f9 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -7552,6 +7552,13 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, > > > > init_emulate_ctxt(vcpu); > > > > + ctxt->interruptibility = 0; > > + ctxt->have_exception = false; > > + ctxt->exception.vector = -1; > > + ctxt->perm_ok = false; > > What about moving this block all the way into init_emulate_ctxt()? > > > + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; > > This can be left where it is since ctxt->ud is consumed only by x86_decode_insn(). > I don't have a strong preference as it really only matters for the backport. For > upstream, we can kill it off in a follow-up patch by passing emulation_type to > x86_decode_insn() and dropping ctxt->ud altogether. Tracking that info in ctxt > for literally one call is silly. Good suggestion, will do in v2. Wanpeng
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index bbc4e04..eca69f9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7552,6 +7552,13 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, init_emulate_ctxt(vcpu); + ctxt->interruptibility = 0; + ctxt->have_exception = false; + ctxt->exception.vector = -1; + ctxt->perm_ok = false; + + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; + /* * We will reenter on the same instruction since we do not set * complete_userspace_io. This does not handle watchpoints yet, @@ -7561,13 +7568,6 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, kvm_vcpu_check_breakpoint(vcpu, &r)) return r; - ctxt->interruptibility = 0; - ctxt->have_exception = false; - ctxt->exception.vector = -1; - ctxt->perm_ok = false; - - ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; - r = x86_decode_insn(ctxt, insn, insn_len); trace_kvm_emulate_insn_start(vcpu);