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Subject[tip: x86/core] objtool: Add straight-line-speculation validation
The following commit has been merged into the x86/core branch of tip:

Commit-ID: 1cc1e4c8aab4213bd4e6353dec2620476a233d6d
Gitweb: https://git.kernel.org/tip/1cc1e4c8aab4213bd4e6353dec2620476a233d6d
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Sat, 04 Dec 2021 14:43:42 +01:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 08 Dec 2021 19:26:50 +01:00

objtool: Add straight-line-speculation validation

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
---
tools/objtool/arch/x86/decode.c | 13 +++++++++----
tools/objtool/builtin-check.c | 3 ++-
tools/objtool/check.c | 14 ++++++++++++++
tools/objtool/include/objtool/arch.h | 1 +
tools/objtool/include/objtool/builtin.h | 2 +-
5 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 4d6d7fc..c10ef78 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -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) {
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 8b38b5d..38070f2 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -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(),
};

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2173582..e28172f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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);
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 589ff58..76bae30 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_TRAP,
INSN_OTHER,
};

diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index 15ac0b7..89ba869 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -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[]);

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