On Mon, May 24, 2021, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@xxxxxxxxxxx> > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation) > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> > --- > 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!
