s390/jump label: add sanity checks

commit 5c6497c50f8d809eac6d01512c291a1f67382abd upstream.

Add sanity checks to verify that only expected code will be replaced.
If the code patterns do not match print the code patterns and panic,
since something went terribly wrong.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 42 insertions, 14 deletions

diff --git a/arch/s390/kernel/jump_label.c b/arch/s390/kernel/jump_label.c
index b987ab2c1541..25aef40584f7 100644
--- a/arch/s390/kernel/jump_label.c
+++ b/arch/s390/kernel/jump_label.c
@@ -22,31 +22,59 @@ struct insn_args {
 	enum jump_label_type type;
 };
 
+static void jump_label_make_nop(struct jump_entry *entry, struct insn *insn)
+{
+	/* brcl 0,0 */
+	insn->opcode = 0xc004;
+	insn->offset = 0;
+}
+
+static void jump_label_make_branch(struct jump_entry *entry, struct insn *insn)
+{
+	/* brcl 15,offset */
+	insn->opcode = 0xc0f4;
+	insn->offset = (entry->target - entry->code) >> 1;
+}
+
+static void jump_label_bug(struct jump_entry *entry, struct insn *insn)
+{
+	unsigned char *ipc = (unsigned char *)entry->code;
+	unsigned char *ipe = (unsigned char *)insn;
+
+	pr_emerg("Jump label code mismatch at %pS [%p]\n", ipc, ipc);
+	pr_emerg("Found:    %02x %02x %02x %02x %02x %02x\n",
+		 ipc[0], ipc[1], ipc[2], ipc[3], ipc[4], ipc[5]);
+	pr_emerg("Expected: %02x %02x %02x %02x %02x %02x\n",
+		 ipe[0], ipe[1], ipe[2], ipe[3], ipe[4], ipe[5]);
+	panic("Corrupted kernel text");
+}
+
 static void __jump_label_transform(struct jump_entry *entry,
-				   enum jump_label_type type)
+				   enum jump_label_type type,
+				   int init)
 {
-	struct insn insn;
-	int rc;
+	struct insn old, new;
 
 	if (type == JUMP_LABEL_ENABLE) {
-		/* brcl 15,offset */
-		insn.opcode = 0xc0f4;
-		insn.offset = (entry->target - entry->code) >> 1;
+		jump_label_make_nop(entry, &old);
+		jump_label_make_branch(entry, &new);
 	} else {
-		/* brcl 0,0 */
-		insn.opcode = 0xc004;
-		insn.offset = 0;
+		if (init)
+			jump_label_make_nop(entry, &old);
+		else
+			jump_label_make_branch(entry, &old);
+		jump_label_make_nop(entry, &new);
 	}
-
-	rc = probe_kernel_write((void *)entry->code, &insn, JUMP_LABEL_NOP_SIZE);
-	WARN_ON_ONCE(rc < 0);
+	if (memcmp((void *)entry->code, &old, sizeof(old)))
+		jump_label_bug(entry, &old);
+	probe_kernel_write((void *)entry->code, &new, sizeof(new));
 }
 
 static int __sm_arch_jump_label_transform(void *data)
 {
 	struct insn_args *args = data;
 
-	__jump_label_transform(args->entry, args->type);
+	__jump_label_transform(args->entry, args->type, 0);
 	return 0;
 }
 
@@ -64,7 +92,7 @@ void arch_jump_label_transform(struct jump_entry *entry,
 void arch_jump_label_transform_static(struct jump_entry *entry,
 				      enum jump_label_type type)
 {
-	__jump_label_transform(entry, type);
+	__jump_label_transform(entry, type, 1);
 }
 
 #endif