Il 08/09/2013 11:54, Gleb Natapov ha scritto:
> On Thu, Sep 05, 2013 at 02:21:54PM +0200, Paolo Bonzini wrote:
>> A guest can still attempt to save and restore XSAVE states even if they
>> have been masked in CPUID leaf 0Dh. This usually is not visible to
>> the guest, but is still wrong: "Any attempt to set a reserved bit (as
>> determined by the contents of EAX and EDX after executing CPUID with
>> EAX=0DH, ECX= 0H) in XCR0 for a given processor will result in a #GP
>> exception".
>>
>> The patch also performs the same checks as __kvm_set_xcr in KVM_SET_XSAVE.
>> This catches migration from newer to older kernel/processor before the
>> guest starts running.
>>
>> Cc: kvm@xxxxxxxxxxxxxxx
>> Cc: Gleb Natapov <gleb@xxxxxxxxxx>
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/cpuid.c | 2 +-
>> arch/x86/kvm/x86.c | 10 ++++++++--
>> arch/x86/kvm/x86.h | 1 +
>> 3 files changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index a20ecb5..d7c465d 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -182,7 +182,7 @@ static bool supported_xcr0_bit(unsigned bit)
>> {
>> u64 mask = ((u64)1 << bit);
>>
>> - return mask & (XSTATE_FP | XSTATE_SSE | XSTATE_YMM) & host_xcr0;
>> + return mask & KVM_SUPPORTED_XCR0 & host_xcr0;
>> }
>>
>> #define F(x) bit(X86_FEATURE_##x)
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 3625798..801a882 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -586,6 +586,8 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
>> return 1;
>> if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
>> return 1;
>> + if (xcr0 & ~KVM_SUPPORTED_XCR0)
>> + return 1;
> Shouldn't we check guest's cpuid here?
Yes.
>> if (xcr0 & ~host_xcr0)
>> return 1;
>> kvm_put_guest_xcr0(vcpu);
>> @@ -2980,10 +2982,14 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
>> u64 xstate_bv =
>> *(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)];
>>
>> - if (cpu_has_xsave)
>> + if (cpu_has_xsave) {
>> + if (xstate_bv & ~KVM_SUPPORTED_XCR0)
>> + return -EINVAL;
>> + if (xstate_bv & ~host_xcr0)
>> + return -EINVAL;
> And here?
Here it'd be nice, but we cannot due to backwards compatibility. We
agreed to change KVM_GET_XSAVE and make it only report states that are
included in CPUID, but we still need to do migration from old kernels
that report all states.
If we change KVM_SET_XSAVE to look at CPUID, and the CPUID does not
include AVX, migration will fail from old kernel (KVM_GET_XSAVE reports
all states) to new kernel (KVM_SET_XSAVES checks against CPUID).
Paolo
>> memcpy(&vcpu->arch.guest_fpu.state->xsave,
>> guest_xsave->region, xstate_size);
>> - else {
>> + } else {
>> if (xstate_bv & ~XSTATE_FPSSE)
>> return -EINVAL;
>> memcpy(&vcpu->arch.guest_fpu.state->fxsave,
>> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>> index e224f7a..587fb9e 100644
>> --- a/arch/x86/kvm/x86.h
>> +++ b/arch/x86/kvm/x86.h
>> @@ -122,6 +122,7 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
>> gva_t addr, void *val, unsigned int bytes,
>> struct x86_exception *exception);
>>
>> +#define KVM_SUPPORTED_XCR0 (XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
>> extern u64 host_xcr0;
>>
>> extern struct static_key kvm_no_apic_vcpu;
>> --
>> 1.8.3.1
>
> --
> Gleb.
> --
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