From: Wanpeng Li <[email protected]>
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: [email protected]
Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation)
Signed-off-by: Wanpeng Li <[email protected]>
---
v3 -> v4:
* warning relative path
* not move ctxt->ud
v2 -> v3:
* squash ctxt->ud
v1 -> v2:
* move the second part emulation context initialization into init_emulate_ctxt()
arch/x86/kvm/x86.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
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);
--
2.7.4
From: Wanpeng Li <[email protected]>
ctxt->ud is consumed only by x86_decode_insn(), we can kill it off by
passing emulation_type to x86_decode_insn() and dropping ctxt->ud
altogether. Tracking that info in ctxt for literally one call is silly.
Suggested-by: Sean Christopherson <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/emulate.c | 5 +++--
arch/x86/kvm/kvm_emulate.h | 3 +--
arch/x86/kvm/x86.c | 4 +---
3 files changed, 5 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 8a0ccdb..5e5de05 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5111,7 +5111,7 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
return rc;
}
-int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
+int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int emulation_type)
{
int rc = X86EMUL_CONTINUE;
int mode = ctxt->mode;
@@ -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 f016838..3e870bf 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;
@@ -491,7 +490,7 @@ enum x86_intercept {
#define X86EMUL_MODE_HOST X86EMUL_MODE_PROT64
#endif
-int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len);
+int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int emulation_type);
bool x86_page_table_writing_insn(struct x86_emulate_ctxt *ctxt);
#define EMULATION_FAILED -1
#define EMULATION_OK 0
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dba8077..d752345 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7566,9 +7566,7 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type,
kvm_vcpu_check_breakpoint(vcpu, &r))
return r;
- ctxt->ud = emulation_type & EMULTYPE_TRAP_UD;
-
- 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;
--
2.7.4
On Thu, May 27, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> 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: [email protected]
> Fixes: 4a1e10d5b5d8 (KVM: x86: handle hardware breakpoints during emulation)
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
Reviewed-by: Sean Christopherson <[email protected]>
On Thu, May 27, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <[email protected]>
>
> ctxt->ud is consumed only by x86_decode_insn(), we can kill it off by
> passing emulation_type to x86_decode_insn() and dropping ctxt->ud
> altogether. Tracking that info in ctxt for literally one call is silly.
>
> Suggested-by: Sean Christopherson <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
Reviewed-by: Sean Christopherson <[email protected]>