objtool: Add straight-line-speculation validation

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>

5 files changed, 29 insertions, 6 deletions

diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index 0031a27b6ad0..e15f6e932b4f 100644
--- 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,
 };
 
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 32a810429306..f7154241a2a5 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -456,6 +456,11 @@ int arch_decode_instruction(const struct elf *elf, const struct section *sec,
 
 		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) {
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index c6d199bfd0ae..758baf918d83 100644
--- 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(),
 };
 
diff --git a/tools/objtool/builtin.h b/tools/objtool/builtin.h
index 85c979caa367..33043fcb16db 100644
--- 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);
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 09e7807f83ee..9943987b24a9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2775,6 +2775,12 @@ 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:
@@ -2818,6 +2824,14 @@ 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(insn, &state);