2018-09-18 23:20:34

by Peng Hao

Subject: [PATCH RESEND] kvm/x86: propagate fetch fault into guest

From: Peng Hao <[email protected]>

When handling ept misconfig exit, it will call emulate instruction
with insn_len = 0. The decode instruction function may return a fetch
fault and should propagate to guest.

The problem will result to emulation fail.
KVM internal error. Suberror: 1
emulation failure
EAX=f81a0024 EBX=f6a07000 ECX=f6a0737c EDX=f8be0118
ESI=f6a0737c EDI=00000021 EBP=f6929f98 ESP=f6929f98
EIP=f8bdd141 EFL=00010086 [--S--P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =007b 00000000 ffffffff 00c0f300 DPL=3 DS [-WA]
CS =0060 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
SS =0068 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
DS =007b 00000000 ffffffff 00c0f300 DPL=3 DS [-WA]
FS =00d8 2c044000 ffffffff 00809300 DPL=0 DS16 [-WA]
GS =0033 081a44c8 01000fff 00d0f300 DPL=3 DS [-WA]
LDT=0000 00000000 ffffffff 00000000
TR =0080 f6ea0c80 0000206b 00008b00 DPL=0 TSS32-busy
GDT= f6e99000 000000ff
IDT= fffbb000 000007ff
CR0=80050033 CR2=b757d000 CR3=35d31000 CR4=001406d0

Signed-off-by: Peng Hao <[email protected]>
Reviewed-by: Jiang Biao <[email protected]>
---
arch/x86/kvm/emulate.c | 5 ++++-
arch/x86/kvm/x86.c | 4 +++-
2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 106482d..aecf9a72 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5105,8 +5105,11 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
memcpy(ctxt->fetch.data, insn, insn_len);
else {
rc = __do_insn_fetch_bytes(ctxt, 1);
- if (rc != X86EMUL_CONTINUE)
+ if (rc != X86EMUL_CONTINUE) {
+ if (rc == X86EMUL_PROPAGATE_FAULT)
+ ctxt->have_exception = true;
return rc;
+ }
}

switch (mode) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 542f631..27072e1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6188,8 +6188,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
if (reexecute_instruction(vcpu, cr2, write_fault_to_spt,
emulation_type))
return EMULATE_DONE;
- if (ctxt->have_exception && inject_emulated_exception(vcpu))
+ if (ctxt->have_exception) {
+ inject_emulated_exception(vcpu);
return EMULATE_DONE;
+ }
if (emulation_type & EMULTYPE_SKIP)
return EMULATE_FAIL;
return handle_emulation_failure(vcpu, emulation_type);
--
1.8.3.1

2018-09-19 14:36:24

by Sean Christopherson

Subject: Re: [PATCH RESEND] kvm/x86: propagate fetch fault into guest

On Tue, 2018-09-18 at 19:03 -0400, Peng Hao wrote:
> From: Peng Hao <[email protected]>
>
> When handling ept misconfig exit, it will call emulate instruction
> with insn_len = 0. The decode instruction function may return a fetch
> fault and should propagate to guest.

What fault is encountered, e.g. #PF, #UD, etc...?  Something like a
#UD at this point should result in an exit to userspace as it means
KVM was unable to emulate an instruction that was successfully
decoded by hardware.
> The problem will result to emulation fail.
> KVM internal error. Suberror: 1
> emulation failure
> EAX=f81a0024 EBX=f6a07000 ECX=f6a0737c EDX=f8be0118
> ESI=f6a0737c EDI=00000021 EBP=f6929f98 ESP=f6929f98
> EIP=f8bdd141 EFL=00010086 [--S--P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =007b 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
> CS =0060 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
> SS =0068 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
> DS =007b 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
> FS =00d8 2c044000 ffffffff 00809300 DPL=0 DS16 [-WA]
> GS =0033 081a44c8 01000fff 00d0f300 DPL=3 DS   [-WA]
> LDT=0000 00000000 ffffffff 00000000
> TR =0080 f6ea0c80 0000206b 00008b00 DPL=0 TSS32-busy
> GDT=     f6e99000 000000ff
> IDT=     fffbb000 000007ff
> CR0=80050033 CR2=b757d000 CR3=35d31000 CR4=001406d0
>
> Signed-off-by: Peng Hao <[email protected]>
> Reviewed-by: Jiang Biao <[email protected]>
> ---
>  arch/x86/kvm/emulate.c | 5 ++++-
>  arch/x86/kvm/x86.c     | 4 +++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 106482d..aecf9a72 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -5105,8 +5105,11 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
>   memcpy(ctxt->fetch.data, insn, insn_len);
>   else {
>   rc = __do_insn_fetch_bytes(ctxt, 1);
> - if (rc != X86EMUL_CONTINUE)
> + if (rc != X86EMUL_CONTINUE) {
> + if (rc == X86EMUL_PROPAGATE_FAULT)
> + ctxt->have_exception = true;
>   return rc;
> + }
>   }
>  
>   switch (mode) {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 542f631..27072e1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6188,8 +6188,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
>   if (reexecute_instruction(vcpu, cr2, write_fault_to_spt,
>   emulation_type))
>   return EMULATE_DONE;
> - if (ctxt->have_exception && inject_emulated_exception(vcpu))
> + if (ctxt->have_exception) {
> + inject_emulated_exception(vcpu);
>   return EMULATE_DONE;
> + }
>   if (emulation_type & EMULTYPE_SKIP)
>   return EMULATE_FAIL;
>   return handle_emulation_failure(vcpu, emulation_type);

2018-09-20 16:32:39

by Paolo Bonzini

Subject: Re: [PATCH RESEND] kvm/x86: propagate fetch fault into guest

On 19/09/2018 16:33, Sean Christopherson wrote:
> On Tue, 2018-09-18 at 19:03 -0400, Peng Hao wrote:
>> From: Peng Hao <[email protected]>
>>
>> When handling ept misconfig exit, it will call emulate instruction
>> with insn_len = 0. The decode instruction function may return a fetch
>> fault and should propagate to guest.
>
> What fault is encountered, e.g. #PF, #UD, etc...?  Something like a
> #UD at this point should result in an exit to userspace as it means
> KVM was unable to emulate an instruction that was successfully
> decoded by hardware.

If it's the same bug as https://lore.kernel.org/patchwork/patch/850077/
it would be a #PF.

Paolo

>> The problem will result to emulation fail.
>> KVM internal error. Suberror: 1
>> emulation failure
>> EAX=f81a0024 EBX=f6a07000 ECX=f6a0737c EDX=f8be0118
>> ESI=f6a0737c EDI=00000021 EBP=f6929f98 ESP=f6929f98
>> EIP=f8bdd141 EFL=00010086 [--S--P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
>> ES =007b 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
>> CS =0060 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
>> SS =0068 00000000 ffffffff 00c09300 DPL=0 DS   [-WA]
>> DS =007b 00000000 ffffffff 00c0f300 DPL=3 DS   [-WA]
>> FS =00d8 2c044000 ffffffff 00809300 DPL=0 DS16 [-WA]
>> GS =0033 081a44c8 01000fff 00d0f300 DPL=3 DS   [-WA]
>> LDT=0000 00000000 ffffffff 00000000
>> TR =0080 f6ea0c80 0000206b 00008b00 DPL=0 TSS32-busy
>> GDT=     f6e99000 000000ff
>> IDT=     fffbb000 000007ff
>> CR0=80050033 CR2=b757d000 CR3=35d31000 CR4=001406d0
>>
>> Signed-off-by: Peng Hao <[email protected]>
>> Reviewed-by: Jiang Biao <[email protected]>
>> ---
>>  arch/x86/kvm/emulate.c | 5 ++++-
>>  arch/x86/kvm/x86.c     | 4 +++-
>>  2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>> index 106482d..aecf9a72 100644
>> --- a/arch/x86/kvm/emulate.c
>> +++ b/arch/x86/kvm/emulate.c
>> @@ -5105,8 +5105,11 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
>>   memcpy(ctxt->fetch.data, insn, insn_len);
>>   else {
>>   rc = __do_insn_fetch_bytes(ctxt, 1);
>> - if (rc != X86EMUL_CONTINUE)
>> + if (rc != X86EMUL_CONTINUE) {
>> + if (rc == X86EMUL_PROPAGATE_FAULT)
>> + ctxt->have_exception = true;
>>   return rc;
>> + }
>>   }
>>  
>>   switch (mode) {
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 542f631..27072e1 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -6188,8 +6188,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
>>   if (reexecute_instruction(vcpu, cr2, write_fault_to_spt,
>>   emulation_type))
>>   return EMULATE_DONE;
>> - if (ctxt->have_exception && inject_emulated_exception(vcpu))
>> + if (ctxt->have_exception) {
>> + inject_emulated_exception(vcpu);
>>   return EMULATE_DONE;
>> + }
>>   if (emulation_type & EMULTYPE_SKIP)
>>   return EMULATE_FAIL;
>>   return handle_emulation_failure(vcpu, emulation_type);

2018-09-20 17:43:30

by Sean Christopherson

Subject: Re: [PATCH RESEND] kvm/x86: propagate fetch fault into guest

On Thu, Sep 20, 2018 at 06:32:10PM +0200, Paolo Bonzini wrote:
> On 19/09/2018 16:33, Sean Christopherson wrote:
> > On Tue, 2018-09-18 at 19:03 -0400, Peng Hao wrote:
> >> From: Peng Hao <[email protected]>
> >>
> >> When handling ept misconfig exit, it will call emulate instruction
> >> with insn_len = 0. The decode instruction function may return a fetch
> >> fault and should propagate to guest.
> >
> > What fault is encountered, e.g. #PF, #UD, etc...? ?Something like a
> > #UD at this point should result in an exit to userspace as it means
> > KVM was unable to emulate an instruction that was successfully
> > decoded by hardware.
>
> If it's the same bug as https://lore.kernel.org/patchwork/patch/850077/
> it would be a #PF.

Indeed it is, let's move this discussion to that thread.