Merge branch 'core-objtool-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull objtool updates from Ingo Molnar:
 "This is a series from Peter Zijlstra that adds x86 build-time uaccess
  validation of SMAP to objtool, which will detect and warn about the
  following uaccess API usage bugs and weirdnesses:

   - call to %s() with UACCESS enabled
   - return with UACCESS enabled
   - return with UACCESS disabled from a UACCESS-safe function
   - recursive UACCESS enable
   - redundant UACCESS disable
   - UACCESS-safe disables UACCESS

  As it turns out not leaking uaccess permissions outside the intended
  uaccess functionality is hard when the interfaces are complex and when
  such bugs are mostly dormant.

  As a bonus we now also check the DF flag. We had at least one
  high-profile bug in that area in the early days of Linux, and the
  checking is fairly simple. The checks performed and warnings emitted
  are:

   - call to %s() with DF set
   - return with DF set
   - return with modified stack frame
   - recursive STD
   - redundant CLD

  It's all x86-only for now, but later on this can also be used for PAN
  on ARM and objtool is fairly cross-platform in principle.

  While all warnings emitted by this new checking facility that got
  reported to us were fixed, there might be GCC version dependent
  warnings that were not reported yet - which we'll address, should they
  trigger.

  The warnings are non-fatal build warnings"

* 'core-objtool-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (27 commits)
  mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions
  x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation
  sched/x86_64: Don't save flags on context switch
  objtool: Add Direction Flag validation
  objtool: Add UACCESS validation
  objtool: Fix sibling call detection
  objtool: Rewrite alt->skip_orig
  objtool: Add --backtrace support
  objtool: Rewrite add_ignores()
  objtool: Handle function aliases
  objtool: Set insn->func for alternatives
  x86/uaccess, kcov: Disable stack protector
  x86/uaccess, ftrace: Fix ftrace_likely_update() vs. SMAP
  x86/uaccess, ubsan: Fix UBSAN vs. SMAP
  x86/uaccess, kasan: Fix KASAN vs SMAP
  x86/smap: Ditch __stringify()
  x86/uaccess: Introduce user_access_{save,restore}()
  x86/uaccess, signal: Fix AC=1 bloat
  x86/uaccess: Always inline user_access_begin()
  x86/uaccess, xen: Suppress SMAP warnings
  ...

11 files changed, 382 insertions, 102 deletions

diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index b0d7dc3d71b5..7a111a77b7aa 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -33,7 +33,11 @@
 #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_STD		13
+#define INSN_CLD		14
+#define INSN_OTHER		15
 #define INSN_LAST		INSN_OTHER
 
 enum op_dest_type {
@@ -41,6 +45,7 @@ enum op_dest_type {
 	OP_DEST_REG_INDIRECT,
 	OP_DEST_MEM,
 	OP_DEST_PUSH,
+	OP_DEST_PUSHF,
 	OP_DEST_LEAVE,
 };
 
@@ -55,6 +60,7 @@ enum op_src_type {
 	OP_SRC_REG_INDIRECT,
 	OP_SRC_CONST,
 	OP_SRC_POP,
+	OP_SRC_POPF,
 	OP_SRC_ADD,
 	OP_SRC_AND,
 };
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 540a209b78ab..472e991f6512 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -357,19 +357,26 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
 		/* 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;
 
 	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;
 
@@ -444,6 +451,14 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
 		*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)
 
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 694abc628e9b..f3b378126011 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -29,7 +29,7 @@
 #include "builtin.h"
 #include "check.h"
 
-bool no_fp, no_unreachable, retpoline, module;
+bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess;
 
 static const char * const check_usage[] = {
 	"objtool check [<options>] file.o",
@@ -41,6 +41,8 @@ const struct option check_options[] = {
 	OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),
 	OPT_BOOLEAN('r', "retpoline", &retpoline, "Validate retpoline assumptions"),
 	OPT_BOOLEAN('m', "module", &module, "Indicates the object will be part of a kernel module"),
+	OPT_BOOLEAN('b', "backtrace", &backtrace, "unwind on error"),
+	OPT_BOOLEAN('a', "uaccess", &uaccess, "enable uaccess checking"),
 	OPT_END(),
 };
 
diff --git a/tools/objtool/builtin.h b/tools/objtool/builtin.h
index 28ff40e19a14..69762f9c5602 100644
--- a/tools/objtool/builtin.h
+++ b/tools/objtool/builtin.h
@@ -20,7 +20,7 @@
 #include <subcmd/parse-options.h>
 
 extern const struct option check_options[];
-extern bool no_fp, no_unreachable, retpoline, module;
+extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess;
 
 extern int cmd_check(int argc, const char **argv);
 extern int cmd_orc(int argc, const char **argv);
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 479196aeb409..ac743a1d53ab 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -31,6 +31,7 @@
 struct alternative {
 	struct list_head list;
 	struct instruction *insn;
+	bool skip_orig;
 };
 
 const char *objname;
@@ -105,29 +106,6 @@ static struct instruction *next_insn_same_func(struct objtool_file *file,
 	     insn = next_insn_same_sec(file, insn))
 
 /*
- * Check if the function has been manually whitelisted with the
- * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
- * due to its use of a context switching instruction.
- */
-static bool ignore_func(struct objtool_file *file, struct symbol *func)
-{
-	struct rela *rela;
-
-	/* check for STACK_FRAME_NON_STANDARD */
-	if (file->whitelist && file->whitelist->rela)
-		list_for_each_entry(rela, &file->whitelist->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.
  *
  * For global functions which are outside the scope of this object file, we
@@ -437,18 +415,107 @@ static void add_ignores(struct objtool_file *file)
 	struct instruction *insn;
 	struct section *sec;
 	struct symbol *func;
+	struct rela *rela;
 
-	for_each_sec(file, sec) {
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
+	sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
+	if (!sec)
+		return;
 
-			if (!ignore_func(file, func))
+	list_for_each_entry(rela, &sec->rela_list, list) {
+		switch (rela->sym->type) {
+		case STT_FUNC:
+			func = rela->sym;
+			break;
+
+		case STT_SECTION:
+			func = find_symbol_by_offset(rela->sym->sec, rela->addend);
+			if (!func || func->type != STT_FUNC)
 				continue;
+			break;
 
-			func_for_each_insn_all(file, func, insn)
-				insn->ignore = true;
+		default:
+			WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
+			continue;
 		}
+
+		func_for_each_insn_all(file, func, insn)
+			insn->ignore = true;
+	}
+}
+
+/*
+ * This is a whitelist of functions that is allowed to be called with AC set.
+ * The list is meant to be minimal and only contains compiler instrumentation
+ * ABI and a few functions used to implement *_{to,from}_user() functions.
+ *
+ * These functions must not directly change AC, but may PUSHF/POPF.
+ */
+static const char *uaccess_safe_builtin[] = {
+	/* KASAN */
+	"kasan_report",
+	"check_memory_region",
+	/* KASAN out-of-line */
+	"__asan_loadN_noabort",
+	"__asan_load1_noabort",
+	"__asan_load2_noabort",
+	"__asan_load4_noabort",
+	"__asan_load8_noabort",
+	"__asan_load16_noabort",
+	"__asan_storeN_noabort",
+	"__asan_store1_noabort",
+	"__asan_store2_noabort",
+	"__asan_store4_noabort",
+	"__asan_store8_noabort",
+	"__asan_store16_noabort",
+	/* KASAN in-line */
+	"__asan_report_load_n_noabort",
+	"__asan_report_load1_noabort",
+	"__asan_report_load2_noabort",
+	"__asan_report_load4_noabort",
+	"__asan_report_load8_noabort",
+	"__asan_report_load16_noabort",
+	"__asan_report_store_n_noabort",
+	"__asan_report_store1_noabort",
+	"__asan_report_store2_noabort",
+	"__asan_report_store4_noabort",
+	"__asan_report_store8_noabort",
+	"__asan_report_store16_noabort",
+	/* KCOV */
+	"write_comp_data",
+	"__sanitizer_cov_trace_pc",
+	"__sanitizer_cov_trace_const_cmp1",
+	"__sanitizer_cov_trace_const_cmp2",
+	"__sanitizer_cov_trace_const_cmp4",
+	"__sanitizer_cov_trace_const_cmp8",
+	"__sanitizer_cov_trace_cmp1",
+	"__sanitizer_cov_trace_cmp2",
+	"__sanitizer_cov_trace_cmp4",
+	"__sanitizer_cov_trace_cmp8",
+	/* UBSAN */
+	"ubsan_type_mismatch_common",
+	"__ubsan_handle_type_mismatch",
+	"__ubsan_handle_type_mismatch_v1",
+	/* misc */
+	"csum_partial_copy_generic",
+	"__memcpy_mcsafe",
+	"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
+	NULL
+};
+
+static void add_uaccess_safe(struct objtool_file *file)
+{
+	struct symbol *func;
+	const char **name;
+
+	if (!uaccess)
+		return;
+
+	for (name = uaccess_safe_builtin; *name; name++) {
+		func = find_symbol_by_name(file->elf, *name);
+		if (!func)
+			continue;
+
+		func->alias->uaccess_safe = true;
 	}
 }
 
@@ -458,13 +525,13 @@ static void add_ignores(struct objtool_file *file)
  * But it at least allows objtool to understand the control flow *around* the
  * retpoline.
  */
-static int add_nospec_ignores(struct objtool_file *file)
+static int add_ignore_alternatives(struct objtool_file *file)
 {
 	struct section *sec;
 	struct rela *rela;
 	struct instruction *insn;
 
-	sec = find_section_by_name(file->elf, ".rela.discard.nospec");
+	sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 	if (!sec)
 		return 0;
 
@@ -476,7 +543,7 @@ static int add_nospec_ignores(struct objtool_file *file)
 
 		insn = find_insn(file, rela->sym->sec, rela->addend);
 		if (!insn) {
-			WARN("bad .discard.nospec entry");
+			WARN("bad .discard.ignore_alts entry");
 			return -1;
 		}
 
@@ -525,7 +592,8 @@ static int add_jump_destinations(struct objtool_file *file)
 			continue;
 		} else {
 			/* sibling call */
-			insn->jump_dest = 0;
+			insn->call_dest = rela->sym;
+			insn->jump_dest = NULL;
 			continue;
 		}
 
@@ -547,25 +615,38 @@ static int add_jump_destinations(struct objtool_file *file)
 		}
 
 		/*
-		 * For GCC 8+, create parent/child links for any cold
-		 * subfunctions.  This is _mostly_ redundant with a similar
-		 * initialization in read_symbols().
-		 *
-		 * If a function has aliases, we want the *first* such function
-		 * in the symbol table to be the subfunction's parent.  In that
-		 * case we overwrite the initialization done in read_symbols().
-		 *
-		 * However this code can't completely replace the
-		 * read_symbols() code because this doesn't detect the case
-		 * where the parent function's only reference to a subfunction
-		 * is through a switch table.
+		 * Cross-function jump.
 		 */
 		if (insn->func && insn->jump_dest->func &&
-		    insn->func != insn->jump_dest->func &&
-		    !strstr(insn->func->name, ".cold.") &&
-		    strstr(insn->jump_dest->func->name, ".cold.")) {
-			insn->func->cfunc = insn->jump_dest->func;
-			insn->jump_dest->func->pfunc = insn->func;
+		    insn->func != insn->jump_dest->func) {
+
+			/*
+			 * For GCC 8+, create parent/child links for any cold
+			 * subfunctions.  This is _mostly_ redundant with a
+			 * similar initialization in read_symbols().
+			 *
+			 * If a function has aliases, we want the *first* such
+			 * function in the symbol table to be the subfunction's
+			 * parent.  In that case we overwrite the
+			 * initialization done in read_symbols().
+			 *
+			 * However this code can't completely replace the
+			 * read_symbols() code because this doesn't detect the
+			 * case where the parent function's only reference to a
+			 * subfunction is through a switch table.
+			 */
+			if (!strstr(insn->func->name, ".cold.") &&
+			    strstr(insn->jump_dest->func->name, ".cold.")) {
+				insn->func->cfunc = insn->jump_dest->func;
+				insn->jump_dest->func->pfunc = insn->func;
+
+			} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
+				   insn->jump_dest->offset == insn->jump_dest->func->offset) {
+
+				/* sibling class */
+				insn->call_dest = insn->jump_dest->func;
+				insn->jump_dest = NULL;
+			}
 		}
 	}
 
@@ -634,9 +715,6 @@ static int add_call_destinations(struct objtool_file *file)
  *    conditionally jumps to the _end_ of the entry.  We have to modify these
  *    jumps' destinations to point back to .text rather than the end of the
  *    entry in .altinstr_replacement.
- *
- * 4. It has been requested that we don't validate the !POPCNT feature path
- *    which is a "very very small percentage of machines".
  */
 static int handle_group_alt(struct objtool_file *file,
 			    struct special_alt *special_alt,
@@ -652,9 +730,6 @@ static int handle_group_alt(struct objtool_file *file,
 		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 			break;
 
-		if (special_alt->skip_orig)
-			insn->type = INSN_NOP;
-
 		insn->alt_group = true;
 		last_orig_insn = insn;
 	}
@@ -696,6 +771,7 @@ static int handle_group_alt(struct objtool_file *file,
 		last_new_insn = insn;
 
 		insn->ignore = orig_insn->ignore_alts;
+		insn->func = orig_insn->func;
 
 		if (insn->type != INSN_JUMP_CONDITIONAL &&
 		    insn->type != INSN_JUMP_UNCONDITIONAL)
@@ -818,6 +894,8 @@ static int add_special_section_alts(struct objtool_file *file)
 		}
 
 		alt->insn = new_insn;
+		alt->skip_orig = special_alt->skip_orig;
+		orig_insn->ignore_alts |= special_alt->skip_alt;
 		list_add_tail(&alt->list, &orig_insn->alts);
 
 		list_del(&special_alt->list);
@@ -1239,8 +1317,9 @@ static int decode_sections(struct objtool_file *file)
 		return ret;
 
 	add_ignores(file);
+	add_uaccess_safe(file);
 
-	ret = add_nospec_ignores(file);
+	ret = add_ignore_alternatives(file);
 	if (ret)
 		return ret;
 
@@ -1320,11 +1399,11 @@ static int update_insn_state_regs(struct instruction *insn, struct insn_state *s
 		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 */
@@ -1581,6 +1660,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
 			break;
 
 		case OP_SRC_POP:
+		case OP_SRC_POPF:
 			if (!state->drap && op->dest.type == OP_DEST_REG &&
 			    op->dest.reg == cfa->base) {
 
@@ -1645,6 +1725,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
 		break;
 
 	case OP_DEST_PUSH:
+	case OP_DEST_PUSHF:
 		state->stack_size += 8;
 		if (cfa->base == CFI_SP)
 			cfa->offset += 8;
@@ -1735,7 +1816,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
 		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;
@@ -1799,6 +1880,50 @@ static bool insn_state_match(struct instruction *insn, struct insn_state *state)
 	return false;
 }
 
+static inline bool func_uaccess_safe(struct symbol *func)
+{
+	if (func)
+		return func->alias->uaccess_safe;
+
+	return false;
+}
+
+static inline const char *insn_dest_name(struct instruction *insn)
+{
+	if (insn->call_dest)
+		return insn->call_dest->name;
+
+	return "{dynamic}";
+}
+
+static int validate_call(struct instruction *insn, struct insn_state *state)
+{
+	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
+		WARN_FUNC("call to %s() with UACCESS enabled",
+				insn->sec, insn->offset, insn_dest_name(insn));
+		return 1;
+	}
+
+	if (state->df) {
+		WARN_FUNC("call to %s() with DF set",
+				insn->sec, insn->offset, insn_dest_name(insn));
+		return 1;
+	}
+
+	return 0;
+}
+
+static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
+{
+	if (has_modified_stack_frame(state)) {
+		WARN_FUNC("sibling call from callable instruction with modified stack frame",
+				insn->sec, insn->offset);
+		return 1;
+	}
+
+	return validate_call(insn, state);
+}
+
 /*
  * Follow the branch starting at the given instruction, and recursively follow
  * any other branches (jumps).  Meanwhile, track the frame pointer state at
@@ -1844,7 +1969,9 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 			if (!insn->hint && !insn_state_match(insn, &state))
 				return 1;
 
-			return 0;
+			/* If we were here with AC=0, but now have AC=1, go again */
+			if (insn->state.uaccess || !state.uaccess)
+				return 0;
 		}
 
 		if (insn->hint) {
@@ -1893,16 +2020,42 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 		insn->visited = true;
 
 		if (!insn->ignore_alts) {
+			bool skip_orig = false;
+
 			list_for_each_entry(alt, &insn->alts, list) {
+				if (alt->skip_orig)
+					skip_orig = true;
+
 				ret = validate_branch(file, alt->insn, state);
-				if (ret)
-					return 1;
+				if (ret) {
+					if (backtrace)
+						BT_FUNC("(alt)", insn);
+					return ret;
+				}
 			}
+
+			if (skip_orig)
+				return 0;
 		}
 
 		switch (insn->type) {
 
 		case INSN_RETURN:
+			if (state.uaccess && !func_uaccess_safe(func)) {
+				WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
+				return 1;
+			}
+
+			if (!state.uaccess && func_uaccess_safe(func)) {
+				WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
+				return 1;
+			}
+
+			if (state.df) {
+				WARN_FUNC("return with DF set", sec, insn->offset);
+				return 1;
+			}
+
 			if (func && has_modified_stack_frame(&state)) {
 				WARN_FUNC("return with modified stack frame",
 					  sec, insn->offset);
@@ -1918,17 +2071,22 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 			return 0;
 
 		case INSN_CALL:
-			if (is_fentry_call(insn))
-				break;
+		case INSN_CALL_DYNAMIC:
+			ret = validate_call(insn, &state);
+			if (ret)
+				return ret;
 
-			ret = dead_end_function(file, insn->call_dest);
-			if (ret == 1)
-				return 0;
-			if (ret == -1)
-				return 1;
+			if (insn->type == INSN_CALL) {
+				if (is_fentry_call(insn))
+					break;
+
+				ret = dead_end_function(file, insn->call_dest);
+				if (ret == 1)
+					return 0;
+				if (ret == -1)
+					return 1;
+			}
 
-			/* fallthrough */
-		case INSN_CALL_DYNAMIC:
 			if (!no_fp && func && !has_valid_stack_frame(&state)) {
 				WARN_FUNC("call without frame pointer save/setup",
 					  sec, insn->offset);
@@ -1938,18 +2096,21 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 
 		case INSN_JUMP_CONDITIONAL:
 		case INSN_JUMP_UNCONDITIONAL:
-			if (insn->jump_dest &&
-			    (!func || !insn->jump_dest->func ||
-			     insn->jump_dest->func->pfunc == func)) {
-				ret = validate_branch(file, insn->jump_dest,
-						      state);
+			if (func && !insn->jump_dest) {
+				ret = validate_sibling_call(insn, &state);
 				if (ret)
-					return 1;
+					return ret;
 
-			} else if (func && has_modified_stack_frame(&state)) {
-				WARN_FUNC("sibling call from callable instruction with modified stack frame",
-					  sec, insn->offset);
-				return 1;
+			} else if (insn->jump_dest &&
+				   (!func || !insn->jump_dest->func ||
+				    insn->jump_dest->func->pfunc == func)) {
+				ret = validate_branch(file, insn->jump_dest,
+						      state);
+				if (ret) {
+					if (backtrace)
+						BT_FUNC("(branch)", insn);
+					return ret;
+				}
 			}
 
 			if (insn->type == INSN_JUMP_UNCONDITIONAL)
@@ -1958,11 +2119,10 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 			break;
 
 		case INSN_JUMP_DYNAMIC:
-			if (func && list_empty(&insn->alts) &&
-			    has_modified_stack_frame(&state)) {
-				WARN_FUNC("sibling call from callable instruction with modified stack frame",
-					  sec, insn->offset);
-				return 1;
+			if (func && list_empty(&insn->alts)) {
+				ret = validate_sibling_call(insn, &state);
+				if (ret)
+					return ret;
 			}
 
 			return 0;
@@ -1979,6 +2139,63 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,
 			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:
+			if (state.uaccess) {
+				WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
+				return 1;
+			}
+
+			state.uaccess = true;
+			break;
+
+		case INSN_CLAC:
+			if (!state.uaccess && insn->func) {
+				WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
+				return 1;
+			}
+
+			if (func_uaccess_safe(func) && !state.uaccess_stack) {
+				WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
+				return 1;
+			}
+
+			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:
@@ -2015,6 +2232,8 @@ static int validate_unwind_hints(struct objtool_file *file)
 	for_each_insn(file, insn) {
 		if (insn->hint && !insn->visited) {
 			ret = validate_branch(file, insn, state);
+			if (ret && backtrace)
+				BT_FUNC("<=== (hint)", insn);
 			warnings += ret;
 		}
 	}
@@ -2142,7 +2361,11 @@ static int validate_functions(struct objtool_file *file)
 			if (!insn || insn->ignore)
 				continue;
 
+			state.uaccess = func->alias->uaccess_safe;
+
 			ret = validate_branch(file, insn, state);
+			if (ret && backtrace)
+				BT_FUNC("<=== (func)", insn);
 			warnings += ret;
 		}
 	}
@@ -2199,7 +2422,6 @@ 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.c_file = find_section_by_name(file.elf, ".comment");
 	file.ignore_unreachables = no_unreachable;
 	file.hints = false;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index e6e8a655b556..71e54f97dbcd 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -31,7 +31,8 @@ struct insn_state {
 	int stack_size;
 	unsigned char type;
 	bool bp_scratch;
-	bool drap, end;
+	bool drap, end, uaccess, df;
+	unsigned int uaccess_stack;
 	int drap_reg, drap_offset;
 	struct cfi_reg vals[CFI_NUM_REGS];
 };
@@ -60,7 +61,6 @@ struct objtool_file {
 	struct elf *elf;
 	struct list_head insn_list;
 	DECLARE_HASHTABLE(insn_hash, 16);
-	struct section *whitelist;
 	bool ignore_unreachables, c_file, hints, rodata;
 };
 
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index b8f3cca8e58b..dd198d53387d 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -219,7 +219,7 @@ static int read_sections(struct elf *elf)
 static int read_symbols(struct elf *elf)
 {
 	struct section *symtab, *sec;
-	struct symbol *sym, *pfunc;
+	struct symbol *sym, *pfunc, *alias;
 	struct list_head *entry, *tmp;
 	int symbols_nr, i;
 	char *coldstr;
@@ -239,6 +239,7 @@ static int read_symbols(struct elf *elf)
 			return -1;
 		}
 		memset(sym, 0, sizeof(*sym));
+		alias = sym;
 
 		sym->idx = i;
 
@@ -288,11 +289,17 @@ static int read_symbols(struct elf *elf)
 				break;
 			}
 
-			if (sym->offset == s->offset && sym->len >= s->len) {
-				entry = tmp;
-				break;
+			if (sym->offset == s->offset) {
+				if (sym->len == s->len && alias == sym)
+					alias = s;
+
+				if (sym->len >= s->len) {
+					entry = tmp;
+					break;
+				}
 			}
 		}
+		sym->alias = alias;
 		list_add(&sym->list, entry);
 		hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 	}
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index bc97ed86b9cd..2cc2ed49322d 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -61,7 +61,8 @@ struct symbol {
 	unsigned char bind, type;
 	unsigned long offset;
 	unsigned int len;
-	struct symbol *pfunc, *cfunc;
+	struct symbol *pfunc, *cfunc, *alias;
+	bool uaccess_safe;
 };
 
 struct rela {
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index 50af4e1274b3..4e50563d87c6 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -23,6 +23,7 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "builtin.h"
 #include "special.h"
 #include "warn.h"
 
@@ -42,6 +43,7 @@
 #define ALT_NEW_LEN_OFFSET	11
 
 #define X86_FEATURE_POPCNT (4*32+23)
+#define X86_FEATURE_SMAP   (9*32+20)
 
 struct special_entry {
 	const char *sec;
@@ -110,6 +112,22 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
 		 */
 		if (feature == X86_FEATURE_POPCNT)
 			alt->skip_orig = true;
+
+		/*
+		 * If UACCESS validation is enabled; force that alternative;
+		 * otherwise force it the other way.
+		 *
+		 * What we want to avoid is having both the original and the
+		 * alternative code flow at the same time, in that case we can
+		 * find paths that see the STAC but take the NOP instead of
+		 * CLAC and the other way around.
+		 */
+		if (feature == X86_FEATURE_SMAP) {
+			if (uaccess)
+				alt->skip_orig = true;
+			else
+				alt->skip_alt = true;
+		}
 	}
 
 	orig_rela = find_rela_by_dest(sec, offset + entry->orig);
diff --git a/tools/objtool/special.h b/tools/objtool/special.h
index fad1d092f679..d5c062e718ef 100644
--- a/tools/objtool/special.h
+++ b/tools/objtool/special.h
@@ -26,6 +26,7 @@ struct special_alt {
 
 	bool group;
 	bool skip_orig;
+	bool skip_alt;
 	bool jump_or_nop;
 
 	struct section *orig_sec;
diff --git a/tools/objtool/warn.h b/tools/objtool/warn.h
index afd9f7a05f6d..f4fbb972b611 100644
--- a/tools/objtool/warn.h
+++ b/tools/objtool/warn.h
@@ -64,6 +64,14 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 	free(_str);					\
 })
 
+#define BT_FUNC(format, insn, ...)			\
+({							\
+	struct instruction *_insn = (insn);		\
+	char *_str = offstr(_insn->sec, _insn->offset); \
+	WARN("  %s: " format, _str, ##__VA_ARGS__);	\
+	free(_str);					\
+})
+
 #define WARN_ELF(format, ...)				\
 	WARN(format ": %s", ##__VA_ARGS__, elf_errmsg(-1))