The patch below does not apply to the 5.15-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-5.15.y git checkout FETCH_HEAD git cherry-pick -x 3d80f4c93d3d26d0f9a0dd2844961a632eeea634 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025122954-augmented-paralyses-a384@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 3d80f4c93d3d26d0f9a0dd2844961a632eeea634 Mon Sep 17 00:00:00 2001 From: Yosry Ahmed yosry.ahmed@linux.dev Date: Fri, 24 Oct 2025 19:29:18 +0000 Subject: [PATCH] KVM: nSVM: Avoid incorrect injection of SVM_EXIT_CR0_SEL_WRITE MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit
When emulating L2 instructions, svm_check_intercept() checks whether a write to CR0 should trigger a synthesized #VMEXIT with SVM_EXIT_CR0_SEL_WRITE. However, it does not check whether L1 enabled the intercept for SVM_EXIT_WRITE_CR0, which has higher priority according to the APM (24593—Rev. 3.42—March 2024, Table 15-7):
When both selective and non-selective CR0-write intercepts are active at the same time, the non-selective intercept takes priority. With respect to exceptions, the priority of this intercept is the same as the generic CR0-write intercept.
Make sure L1 does NOT intercept SVM_EXIT_WRITE_CR0 before checking if SVM_EXIT_CR0_SEL_WRITE needs to be injected.
Opportunistically tweak the "not CR0" logic to explicitly bail early so that it's more obvious that only CR0 has a selective intercept, and that modifying icpt_info.exit_code is functionally necessary so that the call to nested_svm_exit_handled() checks the correct exit code.
Fixes: cfec82cb7d31 ("KVM: SVM: Add intercept check for emulated cr accesses") Cc: stable@vger.kernel.org Signed-off-by: Yosry Ahmed yosry.ahmed@linux.dev Link: https://patch.msgid.link/20251024192918.3191141-4-yosry.ahmed@linux.dev [sean: isolate non-CR0 write logic, tweak comments accordingly] Signed-off-by: Sean Christopherson seanjc@google.com
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index bd8df212a59d..1ae7b3c5a7c5 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4535,15 +4535,29 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu, case SVM_EXIT_WRITE_CR0: { unsigned long cr0, val;
- if (info->intercept == x86_intercept_cr_write) + /* + * Adjust the exit code accordingly if a CR other than CR0 is + * being written, and skip straight to the common handling as + * only CR0 has an additional selective intercept. + */ + if (info->intercept == x86_intercept_cr_write && info->modrm_reg) { icpt_info.exit_code += info->modrm_reg; + break; + }
- if (icpt_info.exit_code != SVM_EXIT_WRITE_CR0 || - info->intercept == x86_intercept_clts) + /* + * Convert the exit_code to SVM_EXIT_CR0_SEL_WRITE if a + * selective CR0 intercept is triggered (the common logic will + * treat the selective intercept as being enabled). Note, the + * unconditional intercept has higher priority, i.e. this is + * only relevant if *only* the selective intercept is enabled. + */ + if (vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_CR0_WRITE) || + !(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_SELECTIVE_CR0))) break;
- if (!(vmcb12_is_intercept(&svm->nested.ctl, - INTERCEPT_SELECTIVE_CR0))) + /* CLTS never triggers INTERCEPT_SELECTIVE_CR0 */ + if (info->intercept == x86_intercept_clts) break;
/* LMSW always triggers INTERCEPT_SELECTIVE_CR0 */