[PATCH 7/8] tools/objtool: Check for use of the ENQCMD instruction in the kernel

[Fenghua Yu]

The ENQCMD implicitly accesses the PASID_MSR to fill in the pasid field
of the descriptor being submitted to an accelerator. But there is no
precise (and stable across kernel changes) point at which the PASID_MSR
is updated from the value for one task to the next.

Kernel code that uses accelerators must always use the ENQCMDS instruction
which does not access the PASID_MSR.

Check for use of the ENQCMD instruction in the kernel and warn on its
usage.

Checking the invalid instruction is a relatively new use of objtool and
I'm open to feedback about the approach.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 tools/objtool/arch/x86/decode.c      | 10 +++++++++-
 tools/objtool/check.c                | 20 ++++++++++++++++++++
 tools/objtool/include/objtool/arch.h |  1 +
 3 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index bc821056aba9..e63b44ba3bd4 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -110,7 +110,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 {
 	struct insn insn;
 	int x86_64, ret;
-	unsigned char op1, op2,
+	unsigned char op1, op2, op3,
 		      rex = 0, rex_b = 0, rex_r = 0, rex_w = 0, rex_x = 0,
 		      modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
 		      sib = 0, /* sib_scale = 0, */ sib_index = 0, sib_base = 0;
@@ -137,6 +137,7 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 
 	op1 = insn.opcode.bytes[0];
 	op2 = insn.opcode.bytes[1];
+	op3 = insn.opcode.bytes[2];
 
 	if (insn.rex_prefix.nbytes) {
 		rex = insn.rex_prefix.bytes[0];
@@ -489,6 +490,13 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 			/* nopl/nopw */
 			*type = INSN_NOP;
 
+		} else if (op2 == 0x38 && op3 == 0xf8) {
+			if (insn.prefixes.nbytes == 1 &&
+			    insn.prefixes.bytes[0] == 0xf2) {
+				/* enqcmd */
+				*type = INSN_ENQCMD;
+			}
+
 		} else if (op2 == 0xa0 || op2 == 0xa8) {
 
 			/* push fs/gs */
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e5947fbb9e7a..91d13521d9d6 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3133,6 +3133,21 @@ static int validate_reachable_instructions(struct objtool_file *file)
 	return 0;
 }
 
+static int validate_enqcmd(struct objtool_file *file)
+{
+	struct instruction *insn;
+
+	for_each_insn(file, insn) {
+		if (insn->type == INSN_ENQCMD) {
+			WARN_FUNC("enqcmd instruction", insn->sec,
+				  insn->offset);
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 int check(struct objtool_file *file)
 {
 	int ret, warnings = 0;
@@ -3147,6 +3162,11 @@ int check(struct objtool_file *file)
 	if (list_empty(&file->insn_list))
 		goto out;
 
+	ret = validate_enqcmd(file);
+	if (ret < 0)
+		goto out;
+	warnings += ret;
+
 	if (vmlinux && !validate_dup) {
 		ret = validate_vmlinux_functions(file);
 		if (ret < 0)
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 062bb6e9b865..5147c0762b49 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -26,6 +26,7 @@ enum insn_type {
 	INSN_CLAC,
 	INSN_STD,
 	INSN_CLD,
+	INSN_ENQCMD,
 	INSN_OTHER,
 };
 
-- 
2.33.0