Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch

@@ -5,6 +5,7 @@
 
 #ifdef __KERNEL__
 
+#include <linux/frame.h>
 #include <asm/nops.h>
 
 /*

@@ -135,6 +136,7 @@ static inline void native_wbinvd(void)
 }
 
 extern asmlinkage void native_load_gs_index(unsigned);
+AC_SAFE(native_load_gs_index);
 
 static inline unsigned long __read_cr4(void)
 {

@@ -15,9 +15,14 @@
 	static void __used __section(.discard.func_stack_frame_non_standard) \
 		*__func_stack_frame_non_standard_##func = func
 
+#define AC_SAFE(func) \
+	static void __used __section(.discard.ac_safe) \
+		*__func_ac_safe_##func = func
+
 #else /* !CONFIG_STACK_VALIDATION */
 
 #define STACK_FRAME_NON_STANDARD(func)
+#define AC_SAFE(func)
 
 #endif /* CONFIG_STACK_VALIDATION */
 

@@ -31,7 +31,7 @@ INCLUDES := -I$(srctree)/tools/include \
 	    -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi \
 	    -I$(srctree)/tools/objtool/arch/$(ARCH)/include
 WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed
-CFLAGS   += -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES)
+CFLAGS   += -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) -ggdb3
 LDFLAGS  += -lelf $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
 
 # Allow old libelf to be used:

@@ -33,7 +33,9 @@
 #define INSN_STACK		8
 #define INSN_BUG		9
 #define INSN_NOP		10
-#define INSN_OTHER		11
+#define INSN_STAC		11
+#define INSN_CLAC		12
+#define INSN_OTHER		13
 #define INSN_LAST		INSN_OTHER
 
 enum op_dest_type {

@@ -369,7 +369,19 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
 
 	case 0x0f:
 
-		if (op2 >= 0x80 && op2 <= 0x8f) {
+		if (op2 == 0x01) {
+
+			if (modrm == 0xca) {
+
+				*type = INSN_CLAC;
+
+			} else if (modrm == 0xcb) {
+
+				*type = INSN_STAC;
+
+			}
+
+		} else if (op2 >= 0x80 && op2 <= 0x8f) {
 
 			*type = INSN_JUMP_CONDITIONAL;
 

@@ -127,6 +127,24 @@ static bool ignore_func(struct objtool_file *file, struct symbol *func)
 	return false;
 }
 
+static bool ac_safe_func(struct objtool_file *file, struct symbol *func)
+{
+	struct rela *rela;
+
+	/* check for AC_SAFE */
+	if (file->ac_safe && file->ac_safe->rela)
+		list_for_each_entry(rela, &file->ac_safe->rela->rela_list, list) {
+			if (rela->sym->type == STT_SECTION &&
+			    rela->sym->sec == func->sec &&
+			    rela->addend == func->offset)
+				return true;
+			if (/* rela->sym->type == STT_FUNC && */ rela->sym == func)
+				return true;
+		}
+
+	return false;
+}
+
 /*
  * This checks to see if the given function is a "noreturn" function.
  *

@@ -439,6 +457,8 @@ static void add_ignores(struct objtool_file *file)
 
 	for_each_sec(file, sec) {
 		list_for_each_entry(func, &sec->symbol_list, list) {
+			func->ac_safe = ac_safe_func(file, func);
+
 			if (func->type != STT_FUNC)
 				continue;
 

@@ -1897,11 +1917,16 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 				if (ret)
 					return 1;
 			}
-		}
+		} else printf("ponies\n");
 
 		switch (insn->type) {
 
 		case INSN_RETURN:
+			if (state.ac) {
+				WARN_FUNC("return with AC set", sec, insn->offset);
+				return 1;
+			}
+
 			if (func && has_modified_stack_frame(&state)) {
 				WARN_FUNC("return with modified stack frame",
 					  sec, insn->offset);

@@ -1917,6 +1942,12 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 			return 0;
 
 		case INSN_CALL:
+			if (state.ac && !insn->call_dest->ac_safe) {
+				WARN_FUNC("call to %s() with AC set", sec, insn->offset,
+						insn->call_dest->name);
+				return 1;
+			}
+
 			if (is_fentry_call(insn))
 				break;
 

@@ -1928,6 +1959,11 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 
 			/* fallthrough */
 		case INSN_CALL_DYNAMIC:
+			if (state.ac && !insn->call_dest->ac_safe) {
+				WARN_FUNC("call to %s() with AC set", sec, insn->offset,
+						insn->call_dest->name);
+				return 1;
+			}
 			if (!no_fp && func && !has_valid_stack_frame(&state)) {
 				WARN_FUNC("call without frame pointer save/setup",
 					  sec, insn->offset);

@@ -1980,6 +2016,14 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 
 			break;
 
+		case INSN_STAC:
+			state.ac = true;
+			break;
+
+		case INSN_CLAC:
+			state.ac = false;
+			break;
+
 		default:
 			break;
 		}

@@ -2198,6 +2242,7 @@ int check(const char *_objname, bool orc)
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
 	file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
+	file.ac_safe = find_section_by_name(file.elf, ".discard.ac_safe");
 	file.c_file = find_section_by_name(file.elf, ".comment");
 	file.ignore_unreachables = no_unreachable;
 	file.hints = false;

@@ -31,7 +31,7 @@ struct insn_state {
 	int stack_size;
 	unsigned char type;
 	bool bp_scratch;
-	bool drap, end;
+	bool drap, end, ac;
 	int drap_reg, drap_offset;
 	struct cfi_reg vals[CFI_NUM_REGS];
 };

@@ -61,6 +61,7 @@ struct objtool_file {
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 16);
 	struct section *whitelist;
+	struct section *ac_safe;
 	bool ignore_unreachables, c_file, hints, rodata;
 };
 

@@ -62,6 +62,7 @@ struct symbol {
 	unsigned long offset;
 	unsigned int len;
 	struct symbol *pfunc, *cfunc;
+	bool ac_safe;
 };
 
 struct rela {

@@ -166,8 +166,8 @@ int special_get_alts(struct elf *elf, struct list_head *alts)
 			continue;
 
 		if (sec->len % entry->size != 0) {
-			WARN("%s size not a multiple of %d",
-			     sec->name, entry->size);
+			WARN("%s size (%d) not a multiple of %d",
+			     sec->name, sec->len, entry->size);
 			return -1;
 		}