From 7d209d13e7c3a3d60dc262f11a8ae4e6b4454d30 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 8 Mar 2022 16:30:53 +0100 Subject: [PATCH] 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) Acked-by: Josh Poimboeuf Link: https://lore.kernel.org/r/20220308154319.645963517@infradead.org --- tools/objtool/arch/x86/decode.c | 34 ++++++++++++++++++++++++---- tools/objtool/include/objtool/arch.h | 1 + 2 files changed, 30 insertions(+), 5 deletions(-) diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c index 479e769ca324..943cb41cddf7 100644 --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -103,6 +103,18 @@ unsigned long arch_jump_destination(struct instruction *insn) #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 objtool_file *file, const struct section *sec 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 objtool_file *file, const struct section *sec 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 objtool_file *file, const struct section *sec /* 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 objtool_file *file, const struct section *sec 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) { diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h index 76bae3078286..9b19cc304195 100644 --- 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, }; -- 2.39.5