linux-kernel - [PATCH 8/8] objtool: Add Direction Flag validation

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Date:   Thu, 28 Feb 2019 15:54:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, jpoimboe@...hat.com,
        luto@...nel.org, bp@...en8.de, dvlasenk@...hat.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: [PATCH 8/8] objtool: Add Direction Flag validation

Having DF escape is BAD(tm).

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 tools/objtool/arch.h            |    4 +++-
 tools/objtool/arch/x86/decode.c |    8 ++++++++
 tools/objtool/check.c           |   21 +++++++++++++++++++++
 tools/objtool/check.h           |    2 +-
 4 files changed, 33 insertions(+), 2 deletions(-)

--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -35,7 +35,9 @@
 #define INSN_NOP		10
 #define INSN_STAC		11
 #define INSN_CLAC		12
-#define INSN_OTHER		13
+#define INSN_STD		13
+#define INSN_CLD		14
+#define INSN_OTHER		15
 #define INSN_LAST		INSN_OTHER
 
 enum op_dest_type {
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -456,6 +456,14 @@ int arch_decode_instruction(struct elf *
 		*type = INSN_CALL;
 		break;
 
+	case 0xfc:
+		*type = INSN_CLD;
+		break;
+
+	case 0xfd:
+		*type = INSN_STD;
+		break;
+
 	case 0xff:
 		if (modrm_reg == 2 || modrm_reg == 3)
 
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1930,6 +1930,9 @@ static int validate_branch(struct objtoo
 			if (state.uaccess)
 				WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
 
+			if (state.df)
+				WARN_FUNC("return with DF set", sec, insn->offset);
+
 			if (func && has_modified_stack_frame(&state)) {
 				WARN_FUNC("return with modified stack frame",
 					  sec, insn->offset);
@@ -1951,6 +1954,10 @@ static int validate_branch(struct objtoo
 				WARN_FUNC("call to %s() with UACCESS enabled",
 					  sec, insn->offset, insn_dest_name(insn));
 			}
+			if (state.df) {
+				WARN_FUNC("call to %s() with DF set",
+					  sec, insn->offset, insn_dest_name(insn));
+			}
 
 			if (insn->type == INSN_CALL) {
 				if (is_fentry_call(insn))
@@ -2034,6 +2041,20 @@ static int validate_branch(struct objtoo
 			state.uaccess = false;
 			break;
 
+		case INSN_STD:
+			if (state.df)
+				WARN_FUNC("recursive STD", sec, insn->offset);
+
+			state.df = true;
+			break;
+
+		case INSN_CLD:
+			if (!state.df && insn->func)
+				WARN_FUNC("redundant CLD", sec, insn->offset);
+
+			state.df = false;
+			break;
+
 		default:
 			break;
 		}
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -31,7 +31,7 @@ struct insn_state {
 	int stack_size;
 	unsigned char type;
 	bool bp_scratch;
-	bool drap, end, uaccess, uaccess_safe;
+	bool drap, end, uaccess, uaccess_safe, df;
 	int drap_reg, drap_offset;
 	struct cfi_reg vals[CFI_NUM_REGS];
 };