From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 4 Dec 2021 13:43:42 +0000 (+0100)
Subject: objtool: Add straight-line-speculation validation
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=ee4724cc045fd566b826d292f2cb69e741b9ce7c;p=linux.git

objtool: Add straight-line-speculation validation

[ Upstream commit 1cc1e4c8aab4213bd4e6353dec2620476a233d6d ]

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>
---

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 77b51600e3e94..63ffbc36dacc2 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -529,6 +529,11 @@ 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;
@@ -665,10 +670,10 @@ 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 8b38b5d6fec7b..38070f26105bd 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 58350fe1944b7..e4ed114ba0a76 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2776,6 +2776,12 @@ 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:
@@ -2819,6 +2825,14 @@ 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);
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 478e054fcdf71..9ca08d95e78ee 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 15ac0b7d3d6a3..89ba869ed08fe 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[]);