FAILED: patch "[PATCH] KVM: nSVM: Ignore nCR3[4:0] when loading PDPTEs from memory" failed to apply to 4.19-stable tree

FAILED: patch "[PATCH] KVM: nSVM: Ignore nCR3[4:0] when loading PDPTEs from memory" failed to apply to 4.19-stable tree

[gregkh]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x f559b2e9c5c5308850544ab59396b7d53cfc67bd
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024102849-giggle-five-0241@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

f559b2e9c5c5 ("KVM: nSVM: Ignore nCR3[4:0] when loading PDPTEs from memory")
2732be902353 ("KVM: nSVM: Don't strip host's C-bit from guest's CR3 when reading PDPTRs")
883b0a91f41a ("KVM: SVM: Move Nested SVM Implementation to nested.c")
46a010dd6896 ("kVM SVM: Move SVM related files to own sub-directory")
d55c9d4009c7 ("KVM: nSVM: check for EFER.SVME=1 before entering guest")
0b66465344a7 ("KVM: nSVM: Remove an obsolete comment.")
78f2145c4d93 ("KVM: nSVM: avoid loss of pending IRQ/NMI before entering L2")
b518ba9fa691 ("KVM: nSVM: implement check_nested_events for interrupts")
64b5bd270426 ("KVM: nSVM: ignore L1 interrupt window while running L2 with V_INTR_MASKING=1")
b5ec2e020b70 ("KVM: nSVM: do not change host intercepts while nested VM is running")
689f3bf21628 ("KVM: x86: unify callbacks to load paging root")
257038745cae ("KVM: x86: Move nSVM CPUID 0x8000000A handling into common x86 code")
a50718cc3f43 ("KVM: nSVM: Expose SVM features to L1 iff nested is enabled")
703c335d0693 ("KVM: x86/mmu: Configure max page level during hardware setup")
bde772355958 ("KVM: x86/mmu: Merge kvm_{enable,disable}_tdp() into a common function")
213e0e1f500b ("KVM: SVM: Refactor logging of NPT enabled/disabled")
a1bead2abaa1 ("KVM: VMX: Directly query Intel PT mode when refreshing PMUs")
139085101f85 ("KVM: x86: Use KVM cpu caps to detect MSR_TSC_AUX virt support")
93c380e7b528 ("KVM: x86: Set emulated/transmuted feature bits via kvm_cpu_caps")
bd7919999047 ("KVM: x86: Override host CPUID results with kvm_cpu_caps")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f559b2e9c5c5308850544ab59396b7d53cfc67bd Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Wed, 9 Oct 2024 07:08:38 -0700
Subject: [PATCH] KVM: nSVM: Ignore nCR3[4:0] when loading PDPTEs from memory

Ignore nCR3[4:0] when loading PDPTEs from memory for nested SVM, as bits
4:0 of CR3 are ignored when PAE paging is used, and thus VMRUN doesn't
enforce 32-byte alignment of nCR3.

In the absolute worst case scenario, failure to ignore bits 4:0 can result
in an out-of-bounds read, e.g. if the target page is at the end of a
memslot, and the VMM isn't using guard pages.

Per the APM:

  The CR3 register points to the base address of the page-directory-pointer
  table. The page-directory-pointer table is aligned on a 32-byte boundary,
  with the low 5 address bits 4:0 assumed to be 0.

And the SDM's much more explicit:

  4:0    Ignored

Note, KVM gets this right when loading PDPTRs, it's only the nSVM flow
that is broken.

Fixes: e4e517b4be01 ("KVM: MMU: Do not unconditionally read PDPTE from guest memory")
Reported-by: Kirk Swidowski <swidowski@google.com>
Cc: Andy Nguyen <theflow@google.com>
Cc: 3pvd <3pvd@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20241009140838.1036226-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d5314cb7dff4..cf84103ce38b 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -63,8 +63,12 @@ static u64 nested_svm_get_tdp_pdptr(struct kvm_vcpu *vcpu, int index)
 	u64 pdpte;
 	int ret;
 
+	/*
+	 * Note, nCR3 is "assumed" to be 32-byte aligned, i.e. the CPU ignores
+	 * nCR3[4:0] when loading PDPTEs from memory.
+	 */
 	ret = kvm_vcpu_read_guest_page(vcpu, gpa_to_gfn(cr3), &pdpte,
-				       offset_in_page(cr3) + index * 8, 8);
+				       (cr3 & GENMASK(11, 5)) + index * 8, 8);
 	if (ret)
 		return 0;
 	return pdpte;