Routine check_cr_write() will trigger emulator_get_cpuid()->
kvm_cpuid() to get maxphyaddr, and NULL is passed as values
for ebx/ecx/edx. This is problematic because kvm_cpuid() will
dereference these pointers.
Fixes: d1cd3ce90044 ("KVM: MMU: check guest CR3 reserved bits based on its physical address width.")
Reported-by: Jim Mattson <[email protected]>
Signed-off-by: Yu Zhang <[email protected]>
---
arch/x86/kvm/emulate.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 16bf665..15f527b 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4102,10 +4102,12 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt)
ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
if (efer & EFER_LMA) {
u64 maxphyaddr;
- u32 eax = 0x80000008;
+ u32 eax, ebx, ecx, edx;
- if (ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL,
- NULL, false))
+ eax = 0x80000008;
+ ecx = 0;
+ if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx,
+ &edx, false))
maxphyaddr = eax & 0xff;
else
maxphyaddr = 36;
--
2.5.0
On 18.09.2017 12:45, Yu Zhang wrote:
> Routine check_cr_write() will trigger emulator_get_cpuid()->
> kvm_cpuid() to get maxphyaddr, and NULL is passed as values
> for ebx/ecx/edx. This is problematic because kvm_cpuid() will
> dereference these pointers.
>
> Fixes: d1cd3ce90044 ("KVM: MMU: check guest CR3 reserved bits based on its physical address width.")
> Reported-by: Jim Mattson <[email protected]>
> Signed-off-by: Yu Zhang <[email protected]>
> ---
> arch/x86/kvm/emulate.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 16bf665..15f527b 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4102,10 +4102,12 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt)
> ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
> if (efer & EFER_LMA) {
> u64 maxphyaddr;
> - u32 eax = 0x80000008;
> + u32 eax, ebx, ecx, edx;
>
> - if (ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL,
> - NULL, false))
> + eax = 0x80000008;
> + ecx = 0;
> + if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx,
> + &edx, false))
> maxphyaddr = eax & 0xff;
> else
> maxphyaddr = 36;
>
Not sure if fixing kvm_cpuid() would be better.
Reviewed-by: David Hildenbrand <[email protected]>
--
Thanks,
David
kvm_cpuid ultimately wants to write all four of the GPRs passed in by
reference. I don't see any advantage to allowing some of these
pointers to be NULL.
Reviewed-by: Jim Mattson <[email protected]>
On Mon, Sep 18, 2017 at 5:19 AM, David Hildenbrand <[email protected]> wrote:
> On 18.09.2017 12:45, Yu Zhang wrote:
>> Routine check_cr_write() will trigger emulator_get_cpuid()->
>> kvm_cpuid() to get maxphyaddr, and NULL is passed as values
>> for ebx/ecx/edx. This is problematic because kvm_cpuid() will
>> dereference these pointers.
>>
>> Fixes: d1cd3ce90044 ("KVM: MMU: check guest CR3 reserved bits based on its physical address width.")
>> Reported-by: Jim Mattson <[email protected]>
>> Signed-off-by: Yu Zhang <[email protected]>
>> ---
>> arch/x86/kvm/emulate.c | 8 +++++---
>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>> index 16bf665..15f527b 100644
>> --- a/arch/x86/kvm/emulate.c
>> +++ b/arch/x86/kvm/emulate.c
>> @@ -4102,10 +4102,12 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt)
>> ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
>> if (efer & EFER_LMA) {
>> u64 maxphyaddr;
>> - u32 eax = 0x80000008;
>> + u32 eax, ebx, ecx, edx;
>>
>> - if (ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL,
>> - NULL, false))
>> + eax = 0x80000008;
>> + ecx = 0;
>> + if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx,
>> + &edx, false))
>> maxphyaddr = eax & 0xff;
>> else
>> maxphyaddr = 36;
>>
>
> Not sure if fixing kvm_cpuid() would be better.
>
> Reviewed-by: David Hildenbrand <[email protected]>
>
> --
>
> Thanks,
>
> David
On 9/18/2017 11:56 PM, Jim Mattson wrote:
> kvm_cpuid ultimately wants to write all four of the GPRs passed in by
> reference. I don't see any advantage to allowing some of these
> pointers to be NULL.
Thanks for your comments, Jim & David.
2 reasons I did not choose to change kvm_cpuid():
1> like Jim's comments, kvm_cpuid() will eventually write the *eax -
*edx no matter
a cpuid entry is found or not;
2> currently, return value of kvm_cpuid() is either true when an entry
is found or false
otherwise. We can change kvm_cpuid() to check the pointers of GPRs
against NULL and
return false immediately. Then the false value would have 2 different
meanings - entry
not found, or invalid params.
Paolo, any suggestion? :-)
Thanks
Yu
> Reviewed-by: Jim Mattson <[email protected]>
>
> On Mon, Sep 18, 2017 at 5:19 AM, David Hildenbrand <[email protected]> wrote:
>> On 18.09.2017 12:45, Yu Zhang wrote:
>>> Routine check_cr_write() will trigger emulator_get_cpuid()->
>>> kvm_cpuid() to get maxphyaddr, and NULL is passed as values
>>> for ebx/ecx/edx. This is problematic because kvm_cpuid() will
>>> dereference these pointers.
>>>
>>> Fixes: d1cd3ce90044 ("KVM: MMU: check guest CR3 reserved bits based on its physical address width.")
>>> Reported-by: Jim Mattson <[email protected]>
>>> Signed-off-by: Yu Zhang <[email protected]>
>>> ---
>>> arch/x86/kvm/emulate.c | 8 +++++---
>>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>>> index 16bf665..15f527b 100644
>>> --- a/arch/x86/kvm/emulate.c
>>> +++ b/arch/x86/kvm/emulate.c
>>> @@ -4102,10 +4102,12 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt)
>>> ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
>>> if (efer & EFER_LMA) {
>>> u64 maxphyaddr;
>>> - u32 eax = 0x80000008;
>>> + u32 eax, ebx, ecx, edx;
>>>
>>> - if (ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL,
>>> - NULL, false))
>>> + eax = 0x80000008;
>>> + ecx = 0;
>>> + if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx,
>>> + &edx, false))
>>> maxphyaddr = eax & 0xff;
>>> else
>>> maxphyaddr = 36;
>>>
>> Not sure if fixing kvm_cpuid() would be better.
>>
>> Reviewed-by: David Hildenbrand <[email protected]>
>>
>> --
>>
>> Thanks,
>>
>> David
On 20/09/2017 08:35, Yu Zhang wrote:
>
> 2 reasons I did not choose to change kvm_cpuid(): 1> like Jim's
> comments, kvm_cpuid() will eventually write the *eax - *edx no
> matter a cpuid entry is found or not; 2> currently, return value of
> kvm_cpuid() is either true when an entry is found or false otherwise.
> We can change kvm_cpuid() to check the pointers of GPRs against NULL
> and return false immediately. Then the false value would have 2
> different meanings - entry not found, or invalid params.
>
> Paolo, any suggestion? :-)
Radim, has already sent this version to Linus. :)
Paolo
On 9/20/2017 4:13 PM, Paolo Bonzini wrote:
> On 20/09/2017 08:35, Yu Zhang wrote:
>> 2 reasons I did not choose to change kvm_cpuid(): 1> like Jim's
>> comments, kvm_cpuid() will eventually write the *eax - *edx no
>> matter a cpuid entry is found or not; 2> currently, return value of
>> kvm_cpuid() is either true when an entry is found or false otherwise.
>> We can change kvm_cpuid() to check the pointers of GPRs against NULL
>> and return false immediately. Then the false value would have 2
>> different meanings - entry not found, or invalid params.
>>
>> Paolo, any suggestion? :-)
> Radim, has already sent this version to Linus. :)
Got it. Thanks. :)
Yu
> Paolo
>