FAILED: patch "[PATCH] KVM: SEV: Reject MMIO requests larger than 8 bytes with GHCB" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.12-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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x dcf1b2d4b0564a27e4ca7c654871aab4f9620046
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026060459-alumni-duplex-df4d@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From dcf1b2d4b0564a27e4ca7c654871aab4f9620046 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Fri, 1 May 2026 13:22:28 -0700
Subject: [PATCH] KVM: SEV: Reject MMIO requests larger than 8 bytes with GHCB
 v2+

When using GHCB v2+, reject MMIO requests that are larger than 8 bytes.
Per the GHCB spec:

  SW_EXITINFO2 must be less than or equal to 0x7fffffff for version 1 and
  less than or equal to 0x8 for all other versions.

Fixes: 4af663c2f64a ("KVM: SEV: Allow per-guest configuration of GHCB protocol version")
Cc: stable@vger.kernel.org
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260501202250.2115252-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index fb2174b6d1ba..e6579ca9f364 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -4502,6 +4502,11 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 		if (!len)
 			return 1;
 
+		if (to_kvm_sev_info(vcpu->kvm)->ghcb_version >= 2 && len > 8) {
+			svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
+			return 1;
+		}
+
 		ret = setup_vmgexit_scratch(svm, !is_write, len);
 		if (ret)
 			break;