[PATCH 0/3] KVM: nVMX: nEPT injection fixes and cleanups

[PATCH 0/3] KVM: nVMX: nEPT injection fixes and cleanups

[Sean Christopherson]

Fix a minor bug where KVM doesn't clear EXIT_QUALIFICATION when injecting
an EPT Misconfig into L1, and then move exit_qualification out of
kvm_vcpu_arch to avoid recurrences of the bug fixed by commit d7f0a00e438d
("KVM: VMX: Report up-to-date exit qualification to userspace").

Sean Christopherson (3):
  KVM: nVMX: Clear EXIT_QUALIFICATION when injecting an EPT Misconfig
  KVM: x86: Move nEPT exit_qualification field from kvm_vcpu_arch to
    x86_exception
  KVM: nVMX: Add a sanity check that nested PML Full stems from EPT
    Violations

 arch/x86/include/asm/kvm_host.h |  3 ---
 arch/x86/kvm/kvm_emulate.h      |  1 +
 arch/x86/kvm/mmu/paging_tmpl.h  | 14 +++++++-------
 arch/x86/kvm/vmx/nested.c       | 30 ++++++++++++++++++++++++++----
 arch/x86/kvm/vmx/vmx.c          |  2 --
 5 files changed, 34 insertions(+), 16 deletions(-)


base-commit: 7455665a3521aa7b56245c0a2810f748adc5fdd4
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH 1/3] KVM: nVMX: Clear EXIT_QUALIFICATION when injecting an EPT Misconfig

[Sean Christopherson]

Explicitly clear the EXIT_QUALIFCATION field when injecting an EPT
misconfig into L1, as required by the VMX architecture.  Per the SDM:

  This field is saved for VM exits due to the following causes:
  debug exceptions; page-fault exceptions; start-up IPIs (SIPIs);
  system-management interrupts (SMIs) that arrive immediately after the
  execution of I/O instructions; task switches; INVEPT; INVLPG; INVPCID;
  INVVPID; LGDT; LIDT; LLDT; LTR; SGDT; SIDT; SLDT; STR; VMCLEAR; VMPTRLD;
  VMPTRST; VMREAD; VMWRITE; VMXON; WBINVD; WBNOINVD; XRSTORS; XSAVES;
  control-register accesses; MOV DR; I/O instructions; MWAIT; accesses to
  the APIC-access page; EPT violations; EOI virtualization; APIC-write
  emulation; page-modification log full; SPP-related events; and
  instruction timeout. For all other VM exits, this field is cleared.

Generating EXIT_QUALIFICATION from vcpu->arch.exit_qualification is wrong
for all (two) paths that lead to nested_ept_inject_page_fault().  For EPT
violations (the common case), vcpu->arch.exit_qualification will have been
set by handle_ept_violation() to vmcs02.EXIT_QUALIFICATION, i.e. contains
the information of a EPT violation and thus is likely non-zero.

For an EPT misconfig, which can reach FNAME(walk_addr_generic) and thus
inject a nEPT misconfig if KVM created an MMIO SPTE that became stale,
vcpu->arch.exit_qualification will hold the information from the last EPT
violation VM-Exit, as vcpu->arch.exit_qualification is _only_ written by
handle_ept_violation().

Fixes: 4704d0befb07 ("KVM: nVMX: Exiting from L2 to L1")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/nested.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 994e014f8a50..1eebed84bb65 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -417,10 +417,12 @@ static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu,
 		vmx->nested.pml_full = false;
 		exit_qualification &= INTR_INFO_UNBLOCK_NMI;
 	} else {
-		if (fault->error_code & PFERR_RSVD_MASK)
+		if (fault->error_code & PFERR_RSVD_MASK) {
 			vm_exit_reason = EXIT_REASON_EPT_MISCONFIG;
-		else
+			exit_qualification = 0;
+		} else {
 			vm_exit_reason = EXIT_REASON_EPT_VIOLATION;
+		}
 
 		/*
 		 * Although the caller (kvm_inject_emulated_page_fault) would
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH 2/3] KVM: x86: Move nEPT exit_qualification field from kvm_vcpu_arch to x86_exception

[Sean Christopherson]

Move the exit_qualification field that is used to track information about
in-flight nEPT violations from "struct kvm_vcpu_arch" to "x86_exception",
i.e. associate the information with the actual nEPT violation instead of
the vCPU.  To handle bits that are pulled from vmcs.EXIT_QUALIFICATION,
i.e. that are propagated from the "original" EPT violation VM-Exit, simply
grab them from the VMCS on-demand when injecting a nEPT Violation or a PML
Full VM-exit.

Aside from being ugly, having an exit_qualification field in kvm_vcpu_arch
is outright dangerous, e.g. see commit d7f0a00e438d ("KVM: VMX: Report
up-to-date exit qualification to userspace").

Opportunstically add a comment to call out that PML Full and EPT Violation
VM-Exits use the same bit to report NMI blocking information.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/kvm_host.h |  3 ---
 arch/x86/kvm/kvm_emulate.h      |  1 +
 arch/x86/kvm/mmu/paging_tmpl.h  | 14 +++++++-------
 arch/x86/kvm/vmx/nested.c       | 14 ++++++++++++--
 arch/x86/kvm/vmx/vmx.c          |  2 --
 5 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ad5319a503f0..7ef4715d43d6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -993,9 +993,6 @@ struct kvm_vcpu_arch {
 
 	u64 msr_kvm_poll_control;
 
-	/* set at EPT violation at this point */
-	unsigned long exit_qualification;
-
 	/* pv related host specific info */
 	struct {
 		bool pv_unhalted;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 4351149484fb..b5791a66637e 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -26,6 +26,7 @@ struct x86_exception {
 	bool nested_page_fault;
 	u64 address; /* cr2 or nested page fault gpa */
 	u8 async_page_fault;
+	unsigned long exit_qualification;
 };
 
 /*
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 4d4e98fe4f35..7a87097cb45b 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -497,21 +497,21 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 	 * The other bits are set to 0.
 	 */
 	if (!(errcode & PFERR_RSVD_MASK)) {
-		vcpu->arch.exit_qualification &= (EPT_VIOLATION_GVA_IS_VALID |
-						  EPT_VIOLATION_GVA_TRANSLATED);
+		walker->fault.exit_qualification = 0;
+
 		if (write_fault)
-			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_WRITE;
+			walker->fault.exit_qualification |= EPT_VIOLATION_ACC_WRITE;
 		if (user_fault)
-			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_READ;
+			walker->fault.exit_qualification |= EPT_VIOLATION_ACC_READ;
 		if (fetch_fault)
-			vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_INSTR;
+			walker->fault.exit_qualification |= EPT_VIOLATION_ACC_INSTR;
 
 		/*
 		 * Note, pte_access holds the raw RWX bits from the EPTE, not
 		 * ACC_*_MASK flags!
 		 */
-		vcpu->arch.exit_qualification |= (pte_access & VMX_EPT_RWX_MASK) <<
-						 EPT_VIOLATION_RWX_SHIFT;
+		walker->fault.exit_qualification |= (pte_access & VMX_EPT_RWX_MASK) <<
+						     EPT_VIOLATION_RWX_SHIFT;
 	}
 #endif
 	walker->fault.address = addr;
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 1eebed84bb65..4d0561136e70 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -409,18 +409,28 @@ static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu,
 {
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	unsigned long exit_qualification;
 	u32 vm_exit_reason;
-	unsigned long exit_qualification = vcpu->arch.exit_qualification;
 
 	if (vmx->nested.pml_full) {
 		vm_exit_reason = EXIT_REASON_PML_FULL;
 		vmx->nested.pml_full = false;
-		exit_qualification &= INTR_INFO_UNBLOCK_NMI;
+
+		/*
+		 * PML Full and EPT Violation VM-Exits both use bit 12 to report
+		 * "NMI unblocking due to IRET", i.e. the bit can be propagated
+		 * as-is from the original EXIT_QUALIFICATION.
+		 */
+		exit_qualification = vmx_get_exit_qual(vcpu) & INTR_INFO_UNBLOCK_NMI;
 	} else {
 		if (fault->error_code & PFERR_RSVD_MASK) {
 			vm_exit_reason = EXIT_REASON_EPT_MISCONFIG;
 			exit_qualification = 0;
 		} else {
+			exit_qualification = fault->exit_qualification;
+			exit_qualification |= vmx_get_exit_qual(vcpu) &
+					      (EPT_VIOLATION_GVA_IS_VALID |
+					       EPT_VIOLATION_GVA_TRANSLATED);
 			vm_exit_reason = EXIT_REASON_EPT_VIOLATION;
 		}
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d4e6625e0a9a..a24fba6b7741 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5771,8 +5771,6 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 	error_code |= (exit_qualification & EPT_VIOLATION_GVA_TRANSLATED) != 0 ?
 	       PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
 
-	vcpu->arch.exit_qualification = exit_qualification;
-
 	/*
 	 * Check that the GPA doesn't exceed physical memory limits, as that is
 	 * a guest page fault.  We have to emulate the instruction here, because
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH 3/3] KVM: nVMX: Add a sanity check that nested PML Full stems from EPT Violations

[Sean Christopherson]

Add a WARN_ON_ONCE() sanity check to verify that a nested PML Full VM-Exit
is only synthesized when the original VM-Exit from L2 was an EPT Violation.
While KVM can fallthrough to kvm_mmu_do_page_fault() if an EPT Misconfig
occurs on a stale MMIO SPTE, KVM should not treat the access as a write
(there isn't enough information to know *what* the access was), i.e. KVM
should never try to insert a PML entry in that case.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/nested.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4d0561136e70..29df186dac84 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -416,6 +416,16 @@ static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu,
 		vm_exit_reason = EXIT_REASON_PML_FULL;
 		vmx->nested.pml_full = false;
 
+		/*
+		 * It should be impossible to trigger a nested PML Full VM-Exit
+		 * for anything other than an EPT Violation from L2.  KVM *can*
+		 * trigger nEPT page fault injection in response to an EPT
+		 * Misconfig, e.g. if the MMIO SPTE was stale and L1's EPT
+		 * tables also changed, but KVM should not treat EPT Misconfig
+		 * VM-Exits as writes.
+		 */
+		WARN_ON_ONCE(vmx->exit_reason.basic != EXIT_REASON_EPT_VIOLATION);
+
 		/*
 		 * PML Full and EPT Violation VM-Exits both use bit 12 to report
 		 * "NMI unblocking due to IRET", i.e. the bit can be propagated
-- 
2.43.0.687.g38aa6559b0-goog

Re: [PATCH 0/3] KVM: nVMX: nEPT injection fixes and cleanups

[Sean Christopherson]

On Fri, 09 Feb 2024 14:16:57 -0800, Sean Christopherson wrote:
> Fix a minor bug where KVM doesn't clear EXIT_QUALIFICATION when injecting
> an EPT Misconfig into L1, and then move exit_qualification out of
> kvm_vcpu_arch to avoid recurrences of the bug fixed by commit d7f0a00e438d
> ("KVM: VMX: Report up-to-date exit qualification to userspace").
> 
> Sean Christopherson (3):
>   KVM: nVMX: Clear EXIT_QUALIFICATION when injecting an EPT Misconfig
>   KVM: x86: Move nEPT exit_qualification field from kvm_vcpu_arch to
>     x86_exception
>   KVM: nVMX: Add a sanity check that nested PML Full stems from EPT
>     Violations
> 
> [...]

Applied to kvm-x86 vmx, thanks!

[1/3] KVM: nVMX: Clear EXIT_QUALIFICATION when injecting an EPT Misconfig
      https://github.com/kvm-x86/linux/commit/0c4765140351
[2/3] KVM: x86: Move nEPT exit_qualification field from kvm_vcpu_arch to x86_exception
      https://github.com/kvm-x86/linux/commit/a9466078687f
[3/3] KVM: nVMX: Add a sanity check that nested PML Full stems from EPT Violations
      https://github.com/kvm-x86/linux/commit/23ffe4bbf807

--
https://github.com/kvm-x86/linux/tree/next