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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id m1sm2903200pgd.78.2021.05.27.17.28.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 May 2021 17:28:05 -0700 (PDT) Date: Fri, 28 May 2021 00:28:02 +0000 From: Sean Christopherson To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH v4 1/2] KVM: X86: Fix warning caused by stale emulation context Message-ID: References: <1622160097-37633-1-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1622160097-37633-1-git-send-email-wanpengli@tencent.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 27, 2021, Wanpeng Li wrote: > From: Wanpeng Li > > Reported by syzkaller: > > WARNING: CPU: 7 PID: 10526 at 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 4a1e10d5b5d8 ("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 > --- Reviewed-by: Sean Christopherson