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From: Peter Zijlstra <peterz@infradead.org>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	keescook@chromium.org, hjl.tools@gmail.com,
	andrew.cooper3@citrix.com, mark.rutland@arm.com, will@kernel.org,
	ndesaulniers@google.com
Subject: [PATCH v2 4/6] objtool: Add straight-line-speculation validation
Date: Sat, 04 Dec 2021 14:43:42 +0100	[thread overview]
Message-ID: <20211204134908.023037659@infradead.org> (raw)
In-Reply-To: <20211204134338.760603010@infradead.org>

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>
---
 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(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -531,6 +531,11 @@ int arch_decode_instruction(struct objto
 		}
 		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) {
--- 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(),
 };
 
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3084,6 +3084,12 @@ 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:
@@ -3127,6 +3133,14 @@ 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(file, insn, &state);
--- 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,
 };
 
--- 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[]);
 



  parent reply	other threads:[~2021-12-04 13:54 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-04 13:43 [PATCH v2 0/6] x86: Add stright-line-speculation mitigations Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 1/6] x86/atomic64_386_32: Rename things Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] x86/lib/atomic64_386_32: " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 2/6] x86: Prepare asm files for straight-line-speculation Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 3/6] x86: Prepare inline-asm " Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` Peter Zijlstra [this message]
2021-12-10 11:05   ` [tip: x86/core] objtool: Add straight-line-speculation validation tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 5/6] x86/alternative: Relax text_poke_bp() constraint Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 6/6] x86: Add straight-line-speculation mitigation Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra

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