On Fri, Apr 17, 2020 at 12:38:42PM -0400, Paolo Bonzini wrote:
> When a nested page fault is taken from an address that does not have
> a memslot associated to it, kvm_mmu_do_page_fault returns RET_PF_EMULATE
> (via mmu_set_spte) and kvm_mmu_page_fault then invokes
svm_need_emulation_on_page_fault.
>
> The default answer there is to return false, but in this case this just
> causes the page fault to be retried ad libitum. Since this is not a
> fast path, and the only other case where it is taken is an erratum,
> just stick a kvm_vcpu_gfn_to_memslot check in there to detect the
> common case where the erratum is not happening.
>
> This fixes an infinite loop in the new set_memory_region_test.
>
> Fixes: 05d5a4863525 ("KVM: SVM: Workaround errata#1096 (insn_len
maybe zero on SMAP violation)")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm/svm.c | 7 +++++++
> virt/kvm/kvm_main.c | 1 +
> 2 files changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index a91e397d6750..c86f7278509b 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3837,6 +3837,13 @@ static bool
svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
> bool smap = cr4 & X86_CR4_SMAP;
> bool is_user = svm_get_cpl(vcpu) == 3;
>
> + /*
> + * If RIP is invalid, go ahead with emulation which will cause an
> + * internal error exit.
> + */
> + if (!kvm_vcpu_gfn_to_memslot(vcpu, kvm_rip_read(vcpu) >> PAGE_SHIFT))
When looking into an SEV issue it was noted that the second arg to
kvm_vcpu_gfn_to_memslot() is a gfn_t but kvm_rip_read() will return
guest RIP which is a guest virtual address and memslots hold guest
physical addresses. How is KVM supposed to translate it to a memslot
and indicate if the guest RIP is valid?
Regards,
Liam
