On 5/14/2024 1:31 AM, Sean Christopherson wrote:
On Mon, May 13, 2024, Xiaoyao Li wrote:
On 5/7/2024 11:58 PM, Paolo Bonzini wrote:
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Move the sanity check that hardware never sets bits that collide with KVM-
define synthetic bits from kvm_mmu_page_fault() to npf_interception(),
i.e. make the sanity check #NPF specific. The legacy #PF path already
WARNs if _any_ of bits 63:32 are set, and the error code that comes from
VMX's EPT Violatation and Misconfig is 100% synthesized (KVM morphs VMX's
EXIT_QUALIFICATION into error code flags).
Add a compile-time assert in the legacy #PF handler to make sure that KVM-
define flags are covered by its existing sanity check on the upper bits.
Opportunistically add a description of PFERR_IMPLICIT_ACCESS, since we
are removing the comment that defined it.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
Message-ID: <20240228024147.41573-8-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 6 ++++++
arch/x86/kvm/mmu/mmu.c | 14 +++-----------
arch/x86/kvm/svm/svm.c | 9 +++++++++
3 files changed, 18 insertions(+), 11 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 58bbcf76ad1e..12e727301262 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -267,7 +267,13 @@ enum x86_intercept_stage;
#define PFERR_GUEST_ENC_MASK BIT_ULL(34)
#define PFERR_GUEST_SIZEM_MASK BIT_ULL(35)
#define PFERR_GUEST_VMPL_MASK BIT_ULL(36)
+
+/*
+ * IMPLICIT_ACCESS is a KVM-defined flag used to correctly perform SMAP checks
+ * when emulating instructions that triggers implicit access.
+ */
#define PFERR_IMPLICIT_ACCESS BIT_ULL(48)
+#define PFERR_SYNTHETIC_MASK (PFERR_IMPLICIT_ACCESS)
#define PFERR_NESTED_GUEST_PAGE (PFERR_GUEST_PAGE_MASK | \
PFERR_WRITE_MASK | \
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index c72a2033ca96..5562d693880a 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4502,6 +4502,9 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
return -EFAULT;
#endif
+ /* Ensure the above sanity check also covers KVM-defined flags. */
1. There is no sanity check above related to KVM-defined flags yet. It has
to be after Patch 6.
Ya, it's not just the comment, the entire changelog expects this patch to land
after patch 6.
2. I somehow cannot parse the comment properly, though I know it's to ensure
KVM-defined PFERR_SYNTHETIC_MASK not contain any bit below 32-bits.
Hmm, how about this?
/*
* Ensure that the above sanity check on hardware error code bits 63:32
* also prevents false positives on KVM-defined flags.
*/
Maybe it's just myself inability, I still cannot interpret it well.
Can't we put it above the sanity check of error code, and just with a
comment like
/*
* Ensure KVM-defined flags not occupied any bits below 32-bits,
* that are used by hardware.
* /
