1 files changed, 96 insertions, 96 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9aa324b14d5d..270b507e7098 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -20,8 +20,6 @@
 #include <linux/kernel.h>
 #include <linux/static_call_types.h>
 
-#define FAKE_JUMP_OFFSET -1
-
 struct alternative {
 	struct list_head list;
 	struct instruction *insn;
@@ -775,9 +773,6 @@ static int add_jump_destinations(struct objtool_file *file)
 		if (!is_static_jump(insn))
 			continue;
 
-		if (insn->offset == FAKE_JUMP_OFFSET)
-			continue;
-
 		reloc = find_reloc_by_dest_range(file->elf, insn->sec,
 					       insn->offset, insn->len);
 		if (!reloc) {
@@ -971,28 +966,15 @@ static int add_call_destinations(struct objtool_file *file)
 }
 
 /*
- * The .alternatives section requires some extra special care, over and above
- * what other special sections require:
- *
- * 1. Because alternatives are patched in-place, we need to insert a fake jump
- *    instruction at the end so that validate_branch() skips all the original
- *    replaced instructions when validating the new instruction path.
- *
- * 2. An added wrinkle is that the new instruction length might be zero.  In
- *    that case the old instructions are replaced with noops.  We simulate that
- *    by creating a fake jump as the only new instruction.
- *
- * 3. In some cases, the alternative section includes an instruction which
- *    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.
+ * The .alternatives section requires some extra special care over and above
+ * other special sections because alternatives are patched in place.
  */
 static int handle_group_alt(struct objtool_file *file,
 			    struct special_alt *special_alt,
 			    struct instruction *orig_insn,
 			    struct instruction **new_insn)
 {
-	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
+	struct instruction *last_orig_insn, *last_new_insn = NULL, *insn, *nop = NULL;
 	struct alt_group *orig_alt_group, *new_alt_group;
 	unsigned long dest_off;
 
@@ -1002,6 +984,13 @@ static int handle_group_alt(struct objtool_file *file,
 		WARN("malloc failed");
 		return -1;
 	}
+	orig_alt_group->cfi = calloc(special_alt->orig_len,
+				     sizeof(struct cfi_state *));
+	if (!orig_alt_group->cfi) {
+		WARN("calloc failed");
+		return -1;
+	}
+
 	last_orig_insn = NULL;
 	insn = orig_insn;
 	sec_for_each_insn_from(file, insn) {
@@ -1015,42 +1004,45 @@ static int handle_group_alt(struct objtool_file *file,
 	orig_alt_group->first_insn = orig_insn;
 	orig_alt_group->last_insn = last_orig_insn;
 
-	if (next_insn_same_sec(file, last_orig_insn)) {
-		fake_jump = malloc(sizeof(*fake_jump));
-		if (!fake_jump) {
-			WARN("malloc failed");
-			return -1;
-		}
-		memset(fake_jump, 0, sizeof(*fake_jump));
-		INIT_LIST_HEAD(&fake_jump->alts);
-		INIT_LIST_HEAD(&fake_jump->stack_ops);
-		init_cfi_state(&fake_jump->cfi);
 
-		fake_jump->sec = special_alt->new_sec;
-		fake_jump->offset = FAKE_JUMP_OFFSET;
-		fake_jump->type = INSN_JUMP_UNCONDITIONAL;
-		fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
-		fake_jump->func = orig_insn->func;
+	new_alt_group = malloc(sizeof(*new_alt_group));
+	if (!new_alt_group) {
+		WARN("malloc failed");
+		return -1;
 	}
 
-	if (!special_alt->new_len) {
-		if (!fake_jump) {
-			WARN("%s: empty alternative at end of section",
-			     special_alt->orig_sec->name);
+	if (special_alt->new_len < special_alt->orig_len) {
+		/*
+		 * Insert a fake nop at the end to make the replacement
+		 * alt_group the same size as the original.  This is needed to
+		 * allow propagate_alt_cfi() to do its magic.  When the last
+		 * instruction affects the stack, the instruction after it (the
+		 * nop) will propagate the new state to the shared CFI array.
+		 */
+		nop = malloc(sizeof(*nop));
+		if (!nop) {
+			WARN("malloc failed");
 			return -1;
 		}
+		memset(nop, 0, sizeof(*nop));
+		INIT_LIST_HEAD(&nop->alts);
+		INIT_LIST_HEAD(&nop->stack_ops);
+		init_cfi_state(&nop->cfi);
 
-		*new_insn = fake_jump;
-		return 0;
+		nop->sec = special_alt->new_sec;
+		nop->offset = special_alt->new_off + special_alt->new_len;
+		nop->len = special_alt->orig_len - special_alt->new_len;
+		nop->type = INSN_NOP;
+		nop->func = orig_insn->func;
+		nop->alt_group = new_alt_group;
+		nop->ignore = orig_insn->ignore_alts;
 	}
 
-	new_alt_group = malloc(sizeof(*new_alt_group));
-	if (!new_alt_group) {
-		WARN("malloc failed");
-		return -1;
+	if (!special_alt->new_len) {
+		*new_insn = nop;
+		goto end;
 	}
 
-	last_new_insn = NULL;
 	insn = *new_insn;
 	sec_for_each_insn_from(file, insn) {
 		struct reloc *alt_reloc;
@@ -1089,14 +1081,8 @@ static int handle_group_alt(struct objtool_file *file,
 			continue;
 
 		dest_off = arch_jump_destination(insn);
-		if (dest_off == special_alt->new_off + special_alt->new_len) {
-			if (!fake_jump) {
-				WARN("%s: alternative jump to end of section",
-				     special_alt->orig_sec->name);
-				return -1;
-			}
-			insn->jump_dest = fake_jump;
-		}
+		if (dest_off == special_alt->new_off + special_alt->new_len)
+			insn->jump_dest = next_insn_same_sec(file, last_orig_insn);
 
 		if (!insn->jump_dest) {
 			WARN_FUNC("can't find alternative jump destination",
@@ -1111,13 +1097,13 @@ static int handle_group_alt(struct objtool_file *file,
 		return -1;
 	}
 
+	if (nop)
+		list_add(&nop->list, &last_new_insn->list);
+end:
 	new_alt_group->orig_group = orig_alt_group;
 	new_alt_group->first_insn = *new_insn;
-	new_alt_group->last_insn = last_new_insn;
-
-	if (fake_jump)
-		list_add(&fake_jump->list, &last_new_insn->list);
-
+	new_alt_group->last_insn = nop ? : last_new_insn;
+	new_alt_group->cfi = orig_alt_group->cfi;
 	return 0;
 }
 
@@ -2248,22 +2234,47 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
 	return 0;
 }
 
-static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
+/*
+ * The stack layouts of alternatives instructions can sometimes diverge when
+ * they have stack modifications.  That's fine as long as the potential stack
+ * layouts don't conflict at any given potential instruction boundary.
+ *
+ * Flatten the CFIs of the different alternative code streams (both original
+ * and replacement) into a single shared CFI array which can be used to detect
+ * conflicts and nicely feed a linear array of ORC entries to the unwinder.
+ */
+static int propagate_alt_cfi(struct objtool_file *file, struct instruction *insn)
 {
-	struct stack_op *op;
+	struct cfi_state **alt_cfi;
+	int group_off;
 
-	list_for_each_entry(op, &insn->stack_ops, list) {
-		struct cfi_state old_cfi = state->cfi;
-		int res;
+	if (!insn->alt_group)
+		return 0;
 
-		res = update_cfi_state(insn, &state->cfi, op);
-		if (res)
-			return res;
+	alt_cfi = insn->alt_group->cfi;
+	group_off = insn->offset - insn->alt_group->first_insn->offset;
 
-		if (insn->alt_group && memcmp(&state->cfi, &old_cfi, sizeof(struct cfi_state))) {
-			WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
+	if (!alt_cfi[group_off]) {
+		alt_cfi[group_off] = &insn->cfi;
+	} else {
+		if (memcmp(alt_cfi[group_off], &insn->cfi, sizeof(struct cfi_state))) {
+			WARN_FUNC("stack layout conflict in alternatives",
+				  insn->sec, insn->offset);
 			return -1;
 		}
+	}
+
+	return 0;
+}
+
+static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
+{
+	struct stack_op *op;
+
+	list_for_each_entry(op, &insn->stack_ops, list) {
+
+		if (update_cfi_state(insn, &state->cfi, op))
+			return 1;
 
 		if (op->dest.type == OP_DEST_PUSHF) {
 			if (!state->uaccess_stack) {
@@ -2453,28 +2464,20 @@ static int validate_return(struct symbol *func, struct instruction *insn, struct
 	return 0;
 }
 
-/*
- * Alternatives should not contain any ORC entries, this in turn means they
- * should not contain any CFI ops, which implies all instructions should have
- * the same same CFI state.
- *
- * It is possible to constuct alternatives that have unreachable holes that go
- * unreported (because they're NOPs), such holes would result in CFI_UNDEFINED
- * states which then results in ORC entries, which we just said we didn't want.
- *
- * Avoid them by copying the CFI entry of the first instruction into the whole
- * alternative.
- */
-static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn)
+static struct instruction *next_insn_to_validate(struct objtool_file *file,
+						 struct instruction *insn)
 {
-	struct instruction *first_insn = insn;
 	struct alt_group *alt_group = insn->alt_group;
 
-	sec_for_each_insn_continue(file, insn) {
-		if (insn->alt_group != alt_group)
-			break;
-		insn->cfi = first_insn->cfi;
-	}
+	/*
+	 * Simulate the fact that alternatives are patched in-place.  When the
+	 * end of a replacement alt_group is reached, redirect objtool flow to
+	 * the end of the original alt_group.
+	 */
+	if (alt_group && insn == alt_group->last_insn && alt_group->orig_group)
+		return next_insn_same_sec(file, alt_group->orig_group->last_insn);
+
+	return next_insn_same_sec(file, insn);
 }
 
 /*
@@ -2495,7 +2498,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 	sec = insn->sec;
 
 	while (1) {
-		next_insn = next_insn_same_sec(file, insn);
+		next_insn = next_insn_to_validate(file, insn);
 
 		if (file->c_file && func && insn->func && func != insn->func->pfunc) {
 			WARN("%s() falls through to next function %s()",
@@ -2528,6 +2531,9 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 		insn->visited |= visited;
 
+		if (propagate_alt_cfi(file, insn))
+			return 1;
+
 		if (!insn->ignore_alts && !list_empty(&insn->alts)) {
 			bool skip_orig = false;
 
@@ -2543,9 +2549,6 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 				}
 			}
 
-			if (insn->alt_group)
-				fill_alternative_cfi(file, insn);
-
 			if (skip_orig)
 				return 0;
 		}
@@ -2779,9 +2782,6 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
 	    !strcmp(insn->sec->name, ".altinstr_aux"))
 		return true;
 
-	if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->offset == FAKE_JUMP_OFFSET)
-		return true;
-
 	if (!insn->func)
 		return false;