x86/umip: Fix decoding of register forms of 0F 01 (SGDT and SIDT aliases)

Filter out the register forms of 0F 01 when determining whether or not to
emulate in response to a potential UMIP violation #GP, as SGDT and SIDT only
accept memory operands. The register variants of 0F 01 are used to encode
instructions for things like VMX and SGX, i.e. not checking the Mod field
would cause the kernel to incorrectly emulate on #GP, e.g. due to a CPL
violation on VMLAUNCH.

Fixes: 1e5db223696a ("x86/umip: Add emulation code for UMIP instructions")
Signed-off-by: Sean Christopherson <[e-mail]>
Signed-off-by: Borislav Petkov (AMD) <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Cc: [e-mail]

arch/x86/kernel/umip.c

···
 	if (insn->opcode.bytes[1] == 0x1) {
 		switch (X86_MODRM_REG(insn->modrm.value)) {
 		case 0:
+			/* The reg form of 0F 01 /0 encodes VMX instructions. */
+			if (X86_MODRM_MOD(insn->modrm.value) == 3)
+				return -EINVAL;
+
 			return UMIP_INST_SGDT;
 		case 1:
+			/*
+			 * The reg form of 0F 01 /1 encodes MONITOR/MWAIT,
+			 * STAC/CLAC, and ENCLS.
+			 */
+			if (X86_MODRM_MOD(insn->modrm.value) == 3)
+				return -EINVAL;
+
 			return UMIP_INST_SIDT;
 		case 4:
 			return UMIP_INST_SMSW;