linux-kernel - [PATCH 2/3] KVM: x86: Subsume nested GPA read helper into load

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Message-Id: <20210831164224.1119728-3-seanjc@google.com>
Date:   Tue, 31 Aug 2021 09:42:23 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+200c08e88ae818f849ce@...kaller.appspotmail.com
Subject: [PATCH 2/3] KVM: x86: Subsume nested GPA read helper into load_pdptrs()

Open code the call to mmu->translate_gpa() when loading nested PDPTRs and
kill off the existing helper, kvm_read_guest_page_mmu(), to discourage
incorrect use.  Reading guest memory straight from an L2 GPA is extremely
rare (as evidenced by the lack of users), as very few constructs in x86
specify physical addresses, even fewer are virtualized by KVM, and even
fewer yet require emulation of L2 by L0 KVM.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  3 --
 arch/x86/kvm/x86.c              | 56 +++++++++++----------------------
 2 files changed, 18 insertions(+), 41 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 09b256db394a..ec26a929b94b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1703,9 +1703,6 @@ void kvm_requeue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
 void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
 bool kvm_inject_emulated_page_fault(struct kvm_vcpu *vcpu,
 				    struct x86_exception *fault);
-int kvm_read_guest_page_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-			    gfn_t gfn, void *data, int offset, int len,
-			    u32 access);
 bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl);
 bool kvm_require_dr(struct kvm_vcpu *vcpu, int dr);
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 86539c1686fa..8bd76698be52 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -790,30 +790,6 @@ bool kvm_require_dr(struct kvm_vcpu *vcpu, int dr)
 }
 EXPORT_SYMBOL_GPL(kvm_require_dr);
 
-/*
- * This function will be used to read from the physical memory of the currently
- * running guest. The difference to kvm_vcpu_read_guest_page is that this function
- * can read from guest physical or from the guest's guest physical memory.
- */
-int kvm_read_guest_page_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-			    gfn_t ngfn, void *data, int offset, int len,
-			    u32 access)
-{
-	struct x86_exception exception;
-	gfn_t real_gfn;
-	gpa_t ngpa;
-
-	ngpa     = gfn_to_gpa(ngfn);
-	real_gfn = mmu->translate_gpa(vcpu, ngpa, access, &exception);
-	if (real_gfn == UNMAPPED_GVA)
-		return -EFAULT;
-
-	real_gfn = gpa_to_gfn(real_gfn);
-
-	return kvm_vcpu_read_guest_page(vcpu, real_gfn, data, offset, len);
-}
-EXPORT_SYMBOL_GPL(kvm_read_guest_page_mmu);
-
 static inline u64 pdptr_rsvd_bits(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.reserved_gpa_bits | rsvd_bits(5, 8) | rsvd_bits(1, 2);
@@ -825,34 +801,38 @@ static inline u64 pdptr_rsvd_bits(struct kvm_vcpu *vcpu)
 int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3)
 {
 	gfn_t pdpt_gfn = cr3 >> PAGE_SHIFT;
-	unsigned offset = ((cr3 & (PAGE_SIZE-1)) >> 5) << 2;
+	unsigned offset = (((cr3 & (PAGE_SIZE-1)) >> 5) << 2) * sizeof(u64);
+	gpa_t real_gpa;
 	int i;
 	int ret;
 	u64 pdpte[ARRAY_SIZE(mmu->pdptrs)];
 
-	ret = kvm_read_guest_page_mmu(vcpu, mmu, pdpt_gfn, pdpte,
-				      offset * sizeof(u64), sizeof(pdpte),
-				      PFERR_USER_MASK|PFERR_WRITE_MASK);
-	if (ret < 0) {
-		ret = 0;
-		goto out;
-	}
+	/*
+	 * If the MMU is nested, CR3 holds an L2 GPA and needs to be translated
+	 * to an L1 GPA.
+	 */
+	real_gpa = mmu->translate_gpa(vcpu, gfn_to_gpa(pdpt_gfn),
+				      PFERR_USER_MASK | PFERR_WRITE_MASK, NULL);
+	if (real_gpa == UNMAPPED_GVA)
+		return 0;
+
+	ret = kvm_vcpu_read_guest_page(vcpu, gpa_to_gfn(real_gpa), pdpte,
+				       offset, sizeof(pdpte));
+	if (ret < 0)
+		return 0;
+
 	for (i = 0; i < ARRAY_SIZE(pdpte); ++i) {
 		if ((pdpte[i] & PT_PRESENT_MASK) &&
 		    (pdpte[i] & pdptr_rsvd_bits(vcpu))) {
-			ret = 0;
-			goto out;
+			return 0;
 		}
 	}
-	ret = 1;
 
 	memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
 	kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
 	vcpu->arch.pdptrs_from_userspace = false;
 
-out:
-
-	return ret;
+	return 1;
 }
 EXPORT_SYMBOL_GPL(load_pdptrs);
 
-- 
2.33.0.259.gc128427fd7-goog