* [PATCH v4 2/2] KVM: X86: Kill off ctxt->ud
2021-05-28 0:01 [PATCH v4 1/2] KVM: X86: Fix warning caused by stale emulation context Wanpeng Li
@ 2021-05-28 0:01 ` Wanpeng Li
2021-05-28 0:28 ` Sean Christopherson
2021-05-28 0:28 ` [PATCH v4 1/2] KVM: X86: Fix warning caused by stale emulation context Sean Christopherson
1 sibling, 1 reply; 4+ messages in thread
From: Wanpeng Li @ 2021-05-28 0:01 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: Paolo Bonzini, Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel
From: Wanpeng Li <wanpengli@tencent.com>
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 <seanjc@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v4 1/2] KVM: X86: Fix warning caused by stale emulation context
2021-05-28 0:01 [PATCH v4 1/2] KVM: X86: Fix warning caused by stale emulation context Wanpeng Li
2021-05-28 0:01 ` [PATCH v4 2/2] KVM: X86: Kill off ctxt->ud Wanpeng Li
@ 2021-05-28 0:28 ` Sean Christopherson
1 sibling, 0 replies; 4+ messages in thread
From: Sean Christopherson @ 2021-05-28 0:28 UTC (permalink / raw)
To: Wanpeng Li
Cc: linux-kernel, kvm, Paolo Bonzini, Vitaly Kuznetsov, Wanpeng Li,
Jim Mattson, Joerg Roedel
On Thu, May 27, 2021, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> 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 <wanpengli@tencent.com>
> ---
Reviewed-by: Sean Christopherson <seanjc@google.com>
^ permalink raw reply [flat|nested] 4+ messages in thread