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Subject[PATCH v4 42/45] objtool: Add IBT/ENDBR decoding
Intel IBT requires the target of any indirect CALL or JMP instruction
to be the ENDBR instruction; optionally it allows those two
instructions to have a NOTRACK prefix in order to avoid this
requirement.

The kernel will not enable the use of NOTRACK, as such any occurence
of it in compiler generated code should be flagged.

Teach objtool to Decode ENDBR instructions and WARN about NOTRACK
prefixes.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/arch/x86/decode.c | 34 +++++++++++++++++++++++++++++-----
tools/objtool/include/objtool/arch.h | 1 +
2 files changed, 30 insertions(+), 5 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -103,6 +103,18 @@ unsigned long arch_jump_destination(stru
#define rm_is_mem(reg) (mod_is_mem() && !is_RIP() && rm_is(reg))
#define rm_is_reg(reg) (mod_is_reg() && modrm_rm == (reg))

+static bool has_notrack_prefix(struct insn *insn)
+{
+ int i;
+
+ for (i = 0; i < insn->prefixes.nbytes; i++) {
+ if (insn->prefixes.bytes[i] == 0x3e)
+ return true;
+ }
+
+ return false;
+}
+
int arch_decode_instruction(struct objtool_file *file, const struct section *sec,
unsigned long offset, unsigned int maxlen,
unsigned int *len, enum insn_type *type,
@@ -112,7 +124,7 @@ int arch_decode_instruction(struct objto
const struct elf *elf = file->elf;
struct insn insn;
int x86_64, ret;
- unsigned char op1, op2, op3,
+ unsigned char op1, op2, op3, prefix,
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 +149,8 @@ int arch_decode_instruction(struct objto
if (insn.vex_prefix.nbytes)
return 0;

+ prefix = insn.prefixes.bytes[0];
+
op1 = insn.opcode.bytes[0];
op2 = insn.opcode.bytes[1];
op3 = insn.opcode.bytes[2];
@@ -492,6 +506,12 @@ int arch_decode_instruction(struct objto
/* nopl/nopw */
*type = INSN_NOP;

+ } else if (op2 == 0x1e) {
+
+ if (prefix == 0xf3 && (modrm == 0xfa || modrm == 0xfb))
+ *type = INSN_ENDBR;
+
+
} else if (op2 == 0x38 && op3 == 0xf8) {
if (insn.prefixes.nbytes == 1 &&
insn.prefixes.bytes[0] == 0xf2) {
@@ -636,20 +656,24 @@ int arch_decode_instruction(struct objto
break;

case 0xff:
- if (modrm_reg == 2 || modrm_reg == 3)
+ if (modrm_reg == 2 || modrm_reg == 3) {

*type = INSN_CALL_DYNAMIC;
+ if (has_notrack_prefix(&insn))
+ WARN("notrack prefix found at %s:0x%lx", sec->name, offset);

- else if (modrm_reg == 4)
+ } else if (modrm_reg == 4) {

*type = INSN_JUMP_DYNAMIC;
+ if (has_notrack_prefix(&insn))
+ WARN("notrack prefix found at %s:0x%lx", sec->name, offset);

- else if (modrm_reg == 5)
+ } else if (modrm_reg == 5) {

/* jmpf */
*type = INSN_CONTEXT_SWITCH;

- else if (modrm_reg == 6) {
+ } else if (modrm_reg == 6) {

/* push from mem */
ADD_OP(op) {
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -27,6 +27,7 @@ enum insn_type {
INSN_STD,
INSN_CLD,
INSN_TRAP,
+ INSN_ENDBR,
INSN_OTHER,
};


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