On Mon, Feb 21, 2022, Chenyi Qiang wrote:
> @@ -277,14 +278,18 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> WARN_ON(pfec & (PFERR_PK_MASK | PFERR_RSVD_MASK));
> if (unlikely(mmu->pkr_mask)) {
> u32 pkr_bits, offset;
> + u32 pkr;
>
> /*
> - * PKRU defines 32 bits, there are 16 domains and 2
> - * attribute bits per domain in pkru. pte_pkey is the
> - * index of the protection domain, so pte_pkey * 2 is
> - * is the index of the first bit for the domain.
> + * PKRU and PKRS both define 32 bits. There are 16 domains
> + * and 2 attribute bits per domain in them. pte_key is the
> + * index of the protection domain, so pte_pkey * 2 is the
> + * index of the first bit for the domain. The use of PKRU
> + * versus PKRS is selected by the address type, as determined
> + * by the U/S bit in the paging-structure entries.
> */
> - pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
> + pkr = pte_access & PT_USER_MASK ? vcpu->arch.pkru : kvm_read_pkrs(vcpu);
Blindly reading PKRU/PKRS is wrong. I think this magic insanity will be functionally
correct due to update_pkr_bitmask() clearing the appropriate bits in pkr_mask based
on CR4.PK*, but the read should never happen. PKRU is benign, but I believe reading
PKRS will result in VMREAD to an invalid field if PKRU is supported and enabled, but
PKRS is not supported.
I belive the easiest solution is:
if (pte_access & PT_USER_MASK)
pkr = is_cr4_pke(mmu) ? vcpu->arch.pkru : 0;
else
pkr = is_cr4_pks(mmu) ? kvm_read_pkrs(vcpu) : 0;
The is_cr4_pk*() helpers are restricted to mmu.c, but this presents a good
opportunity to extra the PKR stuff to a separate, non-inline helper (as a prep
patch). E.g.
WARN_ON(pfec & (PFERR_PK_MASK | PFERR_RSVD_MASK));
if (unlikely(mmu->pkr_mask))
u32 pkr_bits = kvm_mmu_pkr_bits(vcpu, mmu, pte_access, pte_pkey);
errcode |= -pkr_bits & PFERR_PK_MASK;
fault |= (pkr_bits != 0);
}
return -(u32)fault & errcode;
permission_fault() is inline because it's heavily used for shadow paging, but
when using TDP, it's far less performance critical. PKR is TDP-only, so moving
it out-of-line should be totally ok (this is also why this patch is "unlikely").
