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objtool: Add straight-line-speculation validation

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Teach objtool to validate the straight-line-speculation constraints:

 - speculation trap after indirect calls
 - speculation trap after RET

Notable: when an instruction is annotated RETPOLINE_SAFE, indicating
  speculation isn't a problem, also don't care about sls for that
  instruction.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134908.023037659@infradead.org
This commit is contained in:
Peter Zijlstra 2021-12-04 14:43:42 +01:00 committed by Borislav Petkov
parent b17c2baa30
commit 1cc1e4c8aa
5 changed files with 27 additions and 6 deletions
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13
tools/objtool/arch/x86/decode.c
View File

@ -531,6 +531,11 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
}
break;
case 0xcc:
/* int3 */
*type = INSN_TRAP;
break;
case 0xe3:
/* jecxz/jrcxz */
*type = INSN_JUMP_CONDITIONAL;
@ -697,10 +702,10 @@ const char *arch_ret_insn(int len)
{
static const char ret[5][5] = {
{ BYTE_RET },
{ BYTE_RET, BYTES_NOP1 },
{ BYTE_RET, BYTES_NOP2 },
{ BYTE_RET, BYTES_NOP3 },
{ BYTE_RET, BYTES_NOP4 },
{ BYTE_RET, 0xcc },
{ BYTE_RET, 0xcc, BYTES_NOP1 },
{ BYTE_RET, 0xcc, BYTES_NOP2 },
{ BYTE_RET, 0xcc, BYTES_NOP3 },
};
if (len < 1 || len > 5) {

3
tools/objtool/builtin-check.c
View File

@ -20,7 +20,7 @@
#include <objtool/objtool.h>
bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
validate_dup, vmlinux, mcount, noinstr, backup;
validate_dup, vmlinux, mcount, noinstr, backup, sls;
static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@ -45,6 +45,7 @@ const struct option check_options[] = {
OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),
OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),
OPT_BOOLEAN('B', "backup", &backup, "create .orig files before modification"),
OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),
OPT_END(),
};

14
tools/objtool/check.c
View File

@ -3084,6 +3084,12 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
switch (insn->type) {
case INSN_RETURN:
if (next_insn && next_insn->type == INSN_TRAP) {
next_insn->ignore = true;
} else if (sls && !insn->retpoline_safe) {
WARN_FUNC("missing int3 after ret",
insn->sec, insn->offset);
}
return validate_return(func, insn, &state);
case INSN_CALL:
@ -3127,6 +3133,14 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
break;
case INSN_JUMP_DYNAMIC:
if (next_insn && next_insn->type == INSN_TRAP) {
next_insn->ignore = true;
} else if (sls && !insn->retpoline_safe) {
WARN_FUNC("missing int3 after indirect jump",
insn->sec, insn->offset);
}
/* fallthrough */
case INSN_JUMP_DYNAMIC_CONDITIONAL:
if (is_sibling_call(insn)) {
ret = validate_sibling_call(file, insn, &state);

1
tools/objtool/include/objtool/arch.h
View File

@ -26,6 +26,7 @@ enum insn_type {
INSN_CLAC,
INSN_STD,
INSN_CLD,
INSN_TRAP,
INSN_OTHER,
};

2
tools/objtool/include/objtool/builtin.h
View File

@ -9,7 +9,7 @@
extern const struct option check_options[];
extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
validate_dup, vmlinux, mcount, noinstr, backup;
validate_dup, vmlinux, mcount, noinstr, backup, sls;
extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);