[PATCH 24/25] objtool: uaccess PUSHF/POPF support

[Peter Zijlstra <peterz@infradead.org>]

Add PUSHF / POPF state.uaccess restore logic. This makes
user_access_save() / user_access_restore() 'work' with objtool.

XXX: should be merged with the previous patch such that KASAN
doesn't explode in between. Split for review.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 tools/objtool/arch.h            |    2 ++
 tools/objtool/arch/x86/decode.c |    4 ++--
 tools/objtool/check.c           |   30 ++++++++++++++++++++++++++----
 tools/objtool/check.h           |    1 +
 4 files changed, 31 insertions(+), 6 deletions(-)

--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -43,6 +43,7 @@ enum op_dest_type {
 	OP_DEST_REG_INDIRECT,
 	OP_DEST_MEM,
 	OP_DEST_PUSH,
+	OP_DEST_PUSHF,
 	OP_DEST_LEAVE,
 };
 
@@ -57,6 +58,7 @@ enum op_src_type {
 	OP_SRC_REG_INDIRECT,
 	OP_SRC_CONST,
 	OP_SRC_POP,
+	OP_SRC_POPF,
 	OP_SRC_ADD,
 	OP_SRC_AND,
 };
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -357,13 +357,13 @@ int arch_decode_instruction(struct elf *
 		/* pushf */
 		*type = INSN_STACK;
 		op->src.type = OP_SRC_CONST;
-		op->dest.type = OP_DEST_PUSH;
+		op->dest.type = OP_DEST_PUSHF;
 		break;
 
 	case 0x9d:
 		/* popf */
 		*type = INSN_STACK;
-		op->src.type = OP_SRC_POP;
+		op->src.type = OP_SRC_POPF;
 		op->dest.type = OP_DEST_MEM;
 		break;
 
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1392,11 +1392,11 @@ static int update_insn_state_regs(struct
 		return 0;
 
 	/* push */
-	if (op->dest.type == OP_DEST_PUSH)
+	if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
 		cfa->offset += 8;
 
 	/* pop */
-	if (op->src.type == OP_SRC_POP)
+	if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
 		cfa->offset -= 8;
 
 	/* add immediate to sp */
@@ -1653,6 +1653,7 @@ static int update_insn_state(struct inst
 			break;
 
 		case OP_SRC_POP:
+		case OP_SRC_POPF:
 			if (!state->drap && op->dest.type == OP_DEST_REG &&
 			    op->dest.reg == cfa->base) {
 
@@ -1717,6 +1718,7 @@ static int update_insn_state(struct inst
 		break;
 
 	case OP_DEST_PUSH:
+	case OP_DEST_PUSHF:
 		state->stack_size += 8;
 		if (cfa->base == CFI_SP)
 			cfa->offset += 8;
@@ -1807,7 +1809,7 @@ static int update_insn_state(struct inst
 		break;
 
 	case OP_DEST_MEM:
-		if (op->src.type != OP_SRC_POP) {
+		if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
 			WARN_FUNC("unknown stack-related memory operation",
 				  insn->sec, insn->offset);
 			return -1;
@@ -2109,6 +2111,26 @@ static int validate_branch(struct objtoo
 			if (update_insn_state(insn, &state))
 				return 1;
 
+			if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
+				if (!state.uaccess_stack) {
+					state.uaccess_stack = 1;
+				} else if (state.uaccess_stack >> 31) {
+					WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
+					return 1;
+				}
+				state.uaccess_stack <<= 1;
+				state.uaccess_stack  |= state.uaccess;
+			}
+
+			if (insn->stack_op.src.type == OP_SRC_POPF) {
+				if (state.uaccess_stack) {
+					state.uaccess = state.uaccess_stack & 1;
+					state.uaccess_stack >>= 1;
+					if (state.uaccess_stack == 1)
+						state.uaccess_stack = 0;
+				}
+			}
+
 			break;
 
 		case INSN_STAC:
@@ -2126,7 +2148,7 @@ static int validate_branch(struct objtoo
 				return 1;
 			}
 
-			if (func_uaccess_safe(func)) {
+			if (func_uaccess_safe(func) && !state.uaccess_stack) {
 				WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
 				return 1;
 			}
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -32,6 +32,7 @@ struct insn_state {
 	unsigned char type;
 	bool bp_scratch;
 	bool drap, end, uaccess;
+	unsigned int uaccess_stack;
 	int drap_reg, drap_offset;
 	struct cfi_reg vals[CFI_NUM_REGS];
 };