From: Wanpeng Li <[email protected]>
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.
syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134683fdd00000
Reported-by: [email protected]
Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation)
Signed-off-by: Wanpeng Li <[email protected]>
---
v2 -> v3:
* squash ctxt->ud
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 bbc4e04..ae47b19 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7226,6 +7226,13 @@ 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;
+
+ ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
+
init_decode_cache(ctxt);
vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
}
@@ -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 Wed, May 26, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> 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]
"/home/kernel/ssd/linux/" can be omitted to make the line length a bit shorter.
checkpatch also complains about using absolute path instead of relative path.
> 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.
>
> syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134683fdd00000
>
> Reported-by: [email protected]
> Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation)
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v2 -> v3:
> * squash ctxt->ud
> 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 bbc4e04..ae47b19 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7226,6 +7226,13 @@ 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;
> +
> + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
"ctxt->ud" should be left where it is in patch 01. "emulation_type" isn't passed
to init_emulate_ctxt(), and I don't see any reason to add it to the params since
ctxt->ud is only consumed by x86_decode_insn(), i.e. moving ctxt->ud isn't
necessary to fix the bug.
arch/x86/kvm/x86.c: In function ‘init_emulate_ctxt’:
arch/x86/kvm/x86.c:7236:13: error: ‘emulation_type’ undeclared (first use in this function); did you mean ‘exception_type’?
7236 | ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
| ^~~~~~~~~~~~~~
| exception_type
arch/x86/kvm/x86.c:7236:13: note: each undeclared identifier is reported only once for each function it appears in
> +
> init_decode_cache(ctxt);
> vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
> }
> @@ -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 Fri, 28 May 2021 at 01:03, Sean Christopherson <[email protected]> wrote:
>
> On Wed, May 26, 2021, Wanpeng Li wrote:
> > From: Wanpeng Li <[email protected]>
> >
> > 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]
>
> "/home/kernel/ssd/linux/" can be omitted to make the line length a bit shorter.
> checkpatch also complains about using absolute path instead of relative path.
>
> > 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.
> >
> > syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134683fdd00000
> >
> > Reported-by: [email protected]
> > Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation)
> > Signed-off-by: Wanpeng Li <[email protected]>
> > ---
> > v2 -> v3:
> > * squash ctxt->ud
> > 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 bbc4e04..ae47b19 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -7226,6 +7226,13 @@ 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;
> > +
> > + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
>
> "ctxt->ud" should be left where it is in patch 01. "emulation_type" isn't passed
I misunderstand your "squashed in" in reply to v2, it seems it should
be not moving "ctxt->ud".
> to init_emulate_ctxt(), and I don't see any reason to add it to the params since
> ctxt->ud is only consumed by x86_decode_insn(), i.e. moving ctxt->ud isn't
> necessary to fix the bug.
>
> arch/x86/kvm/x86.c: In function ‘init_emulate_ctxt’:
> arch/x86/kvm/x86.c:7236:13: error: ‘emulation_type’ undeclared (first use in this function); did you mean ‘exception_type’?
> 7236 | ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
> | ^~~~~~~~~~~~~~
> | exception_type
> arch/x86/kvm/x86.c:7236:13: note: each undeclared identifier is reported only once for each function it appears in
>
> > +
> > init_decode_cache(ctxt);
> > vcpu->arch.emulate_regs_need_sync_from_vcpu = false;
> > }
> > @@ -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 Fri, 28 May 2021 at 01:03, Sean Christopherson <[email protected]> wrote:
>
> On Wed, May 26, 2021, Wanpeng Li wrote:
> > From: Wanpeng Li <[email protected]>
> >
> > 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]
>
> "/home/kernel/ssd/linux/" can be omitted to make the line length a bit shorter.
> checkpatch also complains about using absolute path instead of relative path.
>
> > 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.
> >
> > syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134683fdd00000
> >
> > Reported-by: [email protected]
> > Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation)
> > Signed-off-by: Wanpeng Li <[email protected]>
> > ---
> > v2 -> v3:
> > * squash ctxt->ud
> > 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 bbc4e04..ae47b19 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -7226,6 +7226,13 @@ 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;
> > +
> > + ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
>
> "ctxt->ud" should be left where it is in patch 01. "emulation_type" isn't passed
> to init_emulate_ctxt(), and I don't see any reason to add it to the params since
> ctxt->ud is only consumed by x86_decode_insn(), i.e. moving ctxt->ud isn't
> necessary to fix the bug.
How about this?
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bbc4e04..dba8077 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7226,6 +7226,11 @@ 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;
}
@@ -7561,11 +7566,6 @@ 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);
On Fri, May 28, 2021, Wanpeng Li wrote:
> How about this?
Yep, perfect! Sorry about the squash confusion.
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bbc4e04..dba8077 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7226,6 +7226,11 @@ 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;
> }
> @@ -7561,11 +7566,6 @@ 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);