Paolo Bonzini wrote on 2014-03-27:
> Il 27/03/2014 13:25, Feng Wu ha scritto:
>> +void update_permission_bitmask(struct kvm_vcpu *vcpu,
>> struct kvm_mmu *mmu, bool ept)
>> {
>> unsigned bit, byte, pfec;
>> u8 map;
>> - bool fault, x, w, u, wf, uf, ff, smep;
>> + bool fault, x, w, u, wf, uf, ff, smep, smap;
>>
>> smep = kvm_read_cr4_bits(vcpu, X86_CR4_SMEP); + smap =
>> kvm_read_cr4_bits(vcpu, X86_CR4_SMAP); for (byte = 0; byte <
>> ARRAY_SIZE(mmu->permissions); ++byte) { pfec = byte << 1;
>> map = 0;
>> @@ -3617,11 +3618,26 @@ static void update_permission_bitmask(struct
> kvm_vcpu *vcpu,
>> w |= !is_write_protection(vcpu) && !uf;
>> /* Disallow supervisor fetches of user code if
>> cr4.smep */
>> x &= !(smep && u && !uf);
>> +
>> + /*
>> + * SMAP:kernel-mode data accesses from user-mode
>> + * mappings should fault. A fault is considered
>> + * as a SMAP violation if all of the following
>> + * conditions are ture:
>> + * - X86_CR4_SMAP is set in CR4
>> + * - An user page is accessed
>> + * - !(CPL<3 && X86_EFLAGS_AC is set)
>> + * - Page fault in kernel mode
>> + */
>> + smap = smap && u && !uf &&
>> + !((kvm_x86_ops->get_cpl(vcpu) < 3) &&
>> + ((kvm_x86_ops->get_rflags(vcpu) &
>> + X86_EFLAGS_AC) == 1));
>
> Unfortunately this doesn't work.
>
> The reason is that changing X86_EFLAGS_AC doesn't trigger
> update_permission_bitmask. So the value of CPL < 3 && AC = 1 must not
> be checked in update_permission_bitmask; instead, it must be included
> in the index into the permissions array. You can reuse the
> PFERR_RSVD_MASK bit, like
>
> smapf = pfec & PFERR_RSVD_MASK;
> ...
> smap = smap && smapf u && !uf;
>
> The VCPU can then be passed to permission_fault in order to get the
> value of the CPL and the AC bit.
Is CPL check needed? Shouldn't it already have been covered by U bit?
>
> Please test nested virtualization too. I think PFERR_RSVD_MASK should
> be removed in translate_nested_gpa.
>
> Paolo
Best regards,
Yang
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