FAILED: patch "[PATCH] KVM: VMX: Inject #UD if guest tries to execute SEAMCALL or" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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 <[email protected]>.

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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 9d7dfb95da2cb5c1287df2f3468bcb70d8b31087
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025112029-degree-siesta-988c@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 9d7dfb95da2cb5c1287df2f3468bcb70d8b31087 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Thu, 16 Oct 2025 11:21:47 -0700
Subject: [PATCH] KVM: VMX: Inject #UD if guest tries to execute SEAMCALL or
TDCALL
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Add VMX exit handlers for SEAMCALL and TDCALL to inject a #UD if a non-TD guest attempts to execute SEAMCALL or TDCALL. Neither SEAMCALL nor TDCALL is gated by any software enablement other than VMXON, and so will generate a VM-Exit instead of e.g. a native #UD when executed from the guest kernel.

Note! No unprivileged DoS of the L1 kernel is possible as TDCALL and SEAMCALL #GP at CPL > 0, and the CPL check is performed prior to the VMX non-root (VM-Exit) check, i.e. userspace can't crash the VM. And for a nested guest, KVM forwards unknown exits to L1, i.e. an L2 kernel can crash itself, but not L1.

Note #2! The Intel® Trust Domain CPU Architectural Extensions spec's pseudocode shows the CPL > 0 check for SEAMCALL coming _after_ the VM-Exit, but that appears to be a documentation bug (likely because the CPL > 0 check was incorrectly bundled with other lower-priority #GP checks). Testing on SPR and EMR shows that the CPL > 0 check is performed before the VMX non-root check, i.e. SEAMCALL #GPs when executed in usermode.

Note #3! The aforementioned Trust Domain spec uses confusing pseudocode that says that SEAMCALL will #UD if executed "inSEAM", but "inSEAM" specifically means in SEAM Root Mode, i.e. in the TDX-Module. The long- form description explicitly states that SEAMCALL generates an exit when executed in "SEAM VMX non-root operation". But that's a moot point as the TDX-Module injects #UD if the guest attempts to execute SEAMCALL, as documented in the "Unconditionally Blocked Instructions" section of the TDX-Module base specification.

index 9792e329343e..1baa86dfe029 100644
@@ -93,6 +93,7 @@
 #define EXIT_REASON_TPAUSE              68
 #define EXIT_REASON_BUS_LOCK            74
 #define EXIT_REASON_NOTIFY              75
+#define EXIT_REASON_SEAMCALL            76
 #define EXIT_REASON_TDCALL              77
 #define EXIT_REASON_MSR_READ_IMM        84
 #define EXIT_REASON_MSR_WRITE_IMM       85

index 76271962cb70..bcea087b642f 100644
@@ -6728,6 +6728,14 @@ static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu,
 	case EXIT_REASON_NOTIFY:
 		/* Notify VM exit is not exposed to L1 */
 		return false;
+	case EXIT_REASON_SEAMCALL:
+	case EXIT_REASON_TDCALL:
+		/*
+		 * SEAMCALL and TDCALL unconditionally VM-Exit, but aren't
+		 * virtualized by KVM for L1 hypervisors, i.e. L1 should
+		 * never want or expect such an exit.
+		 */
+		return false;
 	default:
 		return true;
 	}

index f87c216d976d..91b6f2f3edc2 100644
@@ -6032,6 +6032,12 @@ static int handle_vmx_instruction(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static int handle_tdx_instruction(struct kvm_vcpu *vcpu)
+{
+	kvm_queue_exception(vcpu, UD_VECTOR);
+	return 1;
+}
+
 #ifndef CONFIG_X86_SGX_KVM
 static int handle_encls(struct kvm_vcpu *vcpu)
 {

@@ -6157,6 +6163,8 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_ENCLS]		      = handle_encls,
 	[EXIT_REASON_BUS_LOCK]                = handle_bus_lock_vmexit,
 	[EXIT_REASON_NOTIFY]		      = handle_notify,
+	[EXIT_REASON_SEAMCALL]		      = handle_tdx_instruction,
+	[EXIT_REASON_TDCALL]		      = handle_tdx_instruction,
 	[EXIT_REASON_MSR_READ_IMM]            = handle_rdmsr_imm,
 	[EXIT_REASON_MSR_WRITE_IMM]           = handle_wrmsr_imm,
 };