| Message ID | 1621911767-11703-1-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/2] KVM: X86: Fix warning caused by stale emulation context | expand |
On Mon, May 24, 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 the 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 into init_emulate_ctxt() and > before hardware breakpoints check. The ctxt->ud will be dropped by a follow-up > patch. > > 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> > --- > v1 -> v2: > * move the second part emulation context initialization into init_emulate_ctxt() > > 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 bed7b53..3c109d3 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7228,6 +7228,11 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu) > BUILD_BUG_ON(HF_SMM_MASK != X86EMUL_SMM_MASK); > BUILD_BUG_ON(HF_SMM_INSIDE_NMI_MASK != X86EMUL_SMM_INSIDE_NMI_MASK); > > + ctxt->interruptibility = 0; > + ctxt->have_exception = false; > + ctxt->exception.vector = -1; > + ctxt->perm_ok = false; > + > init_decode_cache(ctxt); > vcpu->arch.emulate_regs_need_sync_from_vcpu = false; > } > @@ -7554,6 +7559,8 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, > > init_emulate_ctxt(vcpu); > > + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; Heh, you sent the delta relative to v1. To avoid confusion, can you post v3 with this squashed in? Thanks!
On Thu, 27 May 2021 at 01:52, Sean Christopherson <seanjc@google.com> wrote: > > On Mon, May 24, 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 the 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 into init_emulate_ctxt() and > > before hardware breakpoints check. The ctxt->ud will be dropped by a follow-up > > patch. > > > > 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> > > --- > > v1 -> v2: > > * move the second part emulation context initialization into init_emulate_ctxt() > > > > 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 bed7b53..3c109d3 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -7228,6 +7228,11 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu) > > BUILD_BUG_ON(HF_SMM_MASK != X86EMUL_SMM_MASK); > > BUILD_BUG_ON(HF_SMM_INSIDE_NMI_MASK != X86EMUL_SMM_INSIDE_NMI_MASK); > > > > + ctxt->interruptibility = 0; > > + ctxt->have_exception = false; > > + ctxt->exception.vector = -1; > > + ctxt->perm_ok = false; > > + > > init_decode_cache(ctxt); > > vcpu->arch.emulate_regs_need_sync_from_vcpu = false; > > } > > @@ -7554,6 +7559,8 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type, > > > > init_emulate_ctxt(vcpu); > > > > + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD; > > Heh, you sent the delta relative to v1. To avoid confusion, can you post v3 > with this squashed in? Do it in v3. Wanpeng
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index bed7b53..3c109d3 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7228,6 +7228,11 @@ static void init_emulate_ctxt(struct kvm_vcpu *vcpu) BUILD_BUG_ON(HF_SMM_MASK != X86EMUL_SMM_MASK); BUILD_BUG_ON(HF_SMM_INSIDE_NMI_MASK != X86EMUL_SMM_INSIDE_NMI_MASK); + ctxt->interruptibility = 0; + ctxt->have_exception = false; + ctxt->exception.vector = -1; + ctxt->perm_ok = false; + init_decode_cache(ctxt); vcpu->arch.emulate_regs_need_sync_from_vcpu = false; } @@ -7554,6 +7559,8 @@ 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, @@ -7563,13 +7570,6 @@ 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);