x86/sev: Check for MWAITX and MONITORX opcodes in the #VC handler

jira VULN-756
cve-bf CVE-2024-25742
commit-author Tom Lendacky <[email protected]>
commit e70316d

The MWAITX and MONITORX instructions generate the same #VC error code as
the MWAIT and MONITOR instructions, respectively. Update the #VC handler
opcode checking to also support the MWAITX and MONITORX opcodes.

Fixes: e3ef461 ("x86/sev: Harden #VC instruction emulation somewhat")
	Signed-off-by: Tom Lendacky <[email protected]>
	Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Link: https://lore.kernel.org/r/453d5a7cfb4b9fe818b6fb67f93ae25468bc9e23.1713793161.git.thomas.lendacky@amd.com
(cherry picked from commit e70316d)
	Signed-off-by: Marcin Wcisło <[email protected]>

Author: pvts-mat

arch/x86/kernel/sev-shared.c

@@ -1026,12 +1026,14 @@ static enum es_result vc_check_opcode_bytes(struct es_em_ctxt *ctxt,
 		break;
 
 	case SVM_EXIT_MONITOR:
-		if (opcode == 0x010f && modrm == 0xc8)
+		/* MONITOR and MONITORX instructions generate the same error code */
+		if (opcode == 0x010f && (modrm == 0xc8 || modrm == 0xfa))
 			return ES_OK;
 		break;
 
 	case SVM_EXIT_MWAIT:
-		if (opcode == 0x010f && modrm == 0xc9)
+		/* MWAIT and MWAITX instructions generate the same error code */
+		if (opcode == 0x010f && (modrm == 0xc9 || modrm == 0xfb))
 			return ES_OK;
 		break;