linux-kernel - [PATCH 1/2] KVM: X86: Initialize 'fault' in kvm_fixup_and_inject_pf

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Date:   Fri, 15 Jul 2022 19:42:10 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        jmattson@...gle.com, joro@...tes.org, wanpengli@...cent.com,
        kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] KVM: X86: Initialize 'fault' in kvm_fixup_and_inject_pf_error().

kvm_fixup_and_inject_pf_error() was introduced to fixup the error code(
e.g., to add RSVD flag) and inject the #PF to the guest, when guest
MAXPHYADDR is smaller than the host one.

When it comes to nested, L0 is expected to intercept and fix up the #PF
and then inject to L2 directly if
- L2.MAXPHYADDR < L0.MAXPHYADDR and
- L1 has no intention to intercept L2's #PF (e.g., L2 and L1 have the
  same MAXPHYADDR value && L1 is using EPT for L2),
instead of constructing a #PF VM Exit to L1. Currently, with PFEC_MASK
and PFEC_MATCH both set to 0 in vmcs02, the interception and injection
may happen on all L2 #PFs.

However, failing to initialize 'fault' in kvm_fixup_and_inject_pf_error()
may cause the fault.async_page_fault being NOT zeroed, and later the #PF
being treated as a nested async page fault, and then being injected to L1.
So just fix it by initialize the 'fault' value in the beginning.

Fixes: 897861479c064 ("KVM: x86: Add helper functions for illegal GPA checking and page fault injection")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216178
Reported-by: Yang Lixiao <lixiao.yang@...el.com>
Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 031678eff28e..3246b3c9dfb3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12983,7 +12983,7 @@ EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value);
 void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code)
 {
 	struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
-	struct x86_exception fault;
+	struct x86_exception fault = {0};
 	u64 access = error_code &
 		(PFERR_WRITE_MASK | PFERR_FETCH_MASK | PFERR_USER_MASK);
 
-- 
2.25.1