linux-kernel - [PATCH 5.10 018/100] Revert "KVM: SVM: avoid infinite loop on NPF from bad address"

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Date:   Mon, 31 Jan 2022 11:55:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Liam Merwick <liam.merwick@...cle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.10 018/100] Revert "KVM: SVM: avoid infinite loop on NPF from bad address"

From: Sean Christopherson <seanjc@...gle.com>

commit 31c25585695abdf03d6160aa6d829e855b256329 upstream.

Revert a completely broken check on an "invalid" RIP in SVM's workaround
for the DecodeAssists SMAP errata.  kvm_vcpu_gfn_to_memslot() obviously
expects a gfn, i.e. operates in the guest physical address space, whereas
RIP is a virtual (not even linear) address.  The "fix" worked for the
problematic KVM selftest because the test identity mapped RIP.

Fully revert the hack instead of trying to translate RIP to a GPA, as the
non-SEV case is now handled earlier, and KVM cannot access guest page
tables to translate RIP.

This reverts commit e72436bc3a5206f95bb384e741154166ddb3202e.

Fixes: e72436bc3a52 ("KVM: SVM: avoid infinite loop on NPF from bad address")
Reported-by: Liam Merwick <liam.merwick@...cle.com>
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Liam Merwick <liam.merwick@...cle.com>
Message-Id: <20220120010719.711476-3-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/svm/svm.c |    7 -------
 virt/kvm/kvm_main.c    |    1 -
 2 files changed, 8 deletions(-)

--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4146,13 +4146,6 @@ static bool svm_can_emulate_instruction(
 	if (likely(!insn || insn_len))
 		return true;
 
-	/*
-	 * 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))
-		return true;
-
 	cr4 = kvm_read_cr4(vcpu);
 	smep = cr4 & X86_CR4_SMEP;
 	smap = cr4 & X86_CR4_SMAP;
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1691,7 +1691,6 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_
 {
 	return __gfn_to_memslot(kvm_vcpu_memslots(vcpu), gfn);
 }
-EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
 
 bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 {