[PATCH 5.10 065/130] objtool: Add straight-line-speculation validation

Greg Kroah-Hartman
2022-07-12T18:49:40Z

commit 1cc1e4c8aab4213bd4e6353dec2620476a233d6d upstream.

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 5.10: adjust filenames, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
tools/objtool/arch.h | 1 +
tools/objtool/arch/x86/decode.c | 13 +++++++++----
tools/objtool/builtin-check.c | 4 +++-
tools/objtool/builtin.h | 3 ++-
tools/objtool/check.c | 14 ++++++++++++++
5 files changed, 29 insertions(+), 6 deletions(-)

--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -26,6 +26,7 @@ enum insn_type {
INSN_CLAC,
INSN_STD,
INSN_CLD,
+ INSN_TRAP,
INSN_OTHER,
};

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -456,6 +456,11 @@ int arch_decode_instruction(const struct

break;

+ case 0xcc:
+ /* int3 */
+ *type = INSN_TRAP;
+ break;
+
case 0xe3:
/* jecxz/jrcxz */
*type = INSN_JUMP_CONDITIONAL;
@@ -592,10 +597,10 @@ const char *arch_ret_insn(int len)
{
static const char ret[5][5] = {
{ BYTE_RET },
- { BYTE_RET, 0x90 },
- { BYTE_RET, 0x66, 0x90 },
- { BYTE_RET, 0x0f, 0x1f, 0x00 },
- { BYTE_RET, 0x0f, 0x1f, 0x40, 0x00 },
+ { BYTE_RET, 0xcc },
+ { BYTE_RET, 0xcc, 0x90 },
+ { BYTE_RET, 0xcc, 0x66, 0x90 },
+ { BYTE_RET, 0xcc, 0x0f, 0x1f, 0x00 },
};

if (len < 1 || len > 5) {
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -18,7 +18,8 @@
#include "builtin.h"
#include "objtool.h"

-bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux;
+bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
+ validate_dup, vmlinux, sls;

static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -35,6 +36,7 @@ const struct option check_options[] = {
OPT_BOOLEAN('s', "stats", &stats, "print statistics"),
OPT_BOOLEAN('d', "duplicate", &validate_dup, "duplicate validation for vmlinux.o"),
OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),
+ OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),
OPT_END(),
};

--- a/tools/objtool/builtin.h
+++ b/tools/objtool/builtin.h
@@ -8,7 +8,8 @@
#include <subcmd/parse-options.h>

extern const struct option check_options[];
-extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux;
+extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
+ validate_dup, vmlinux, sls;

extern int cmd_check(int argc, const char **argv);
extern int cmd_orc(int argc, const char **argv);
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2775,6 +2775,12 @@ static int validate_branch(struct objtoo
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:
@@ -2818,6 +2824,14 @@ static int validate_branch(struct objtoo
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(insn, &state);