ARM: kexec: Implement kexec zimage probe

Probe the image to see if it looks like an ARM zImage.

Signed-off-by: Joel Stanley <joel@jms.id.au>

arch/arm/kernel/machine_kexec_file.c

@@ -7,6 +7,61 @@
 
 #include <linux/kexec.h>
 
+struct zimage_header {
+        uint32_t instr[9];
+        uint32_t magic;
+#define ZIMAGE_MAGIC cpu_to_le32(0x016f2818)
+        uint32_t start;
+        uint32_t end;
+        uint32_t endian;
+
+        /* Extension to the data passed to the boot agent.  The offset
+         * points at a tagged table following a similar format to the
+         * ATAGs.
+         */
+        uint32_t magic2;
+#define ZIMAGE_MAGIC2 (0x45454545)
+        uint32_t extension_tag_offset;
+};
+
+static int kexec_zimage_probe(const char *buf, unsigned long len)
+{
+	struct zimage_header *hdr;
+	int size;
+
+	if (len < sizeof(struct zimage_header)) {
+		pr_err("File too short to be a zImage\n");
+		return -ENOEXEC;
+	}
+
+	hdr = (struct zimage_header *)buf;
+
+
+	pr_debug("zImage header: 0x%08x 0x%08x 0x%08x\n", hdr->magic, hdr->start, hdr->end);
+
+	if (hdr->magic != ZIMAGE_MAGIC) {
+		pr_err("Not a zImage\n");
+		return -ENOEXEC;
+	}
+
+	size = le32_to_cpu(hdr->end) - le32_to_cpu(hdr->start);
+
+	pr_debug("zImage size 0x%x, file size 0x%lx\n", size, len);
+
+	if (size > len) {
+		pr_debug("zImage is truncated - file 0x%lx vs header 0x%x\n", len, size);
+		return -ENOEXEC;
+	}
+
+	pr_debug("Found a valid zImage\n");
+
+	return 0;
+}
+
+const struct kexec_file_ops kexec_zimage_ops = {
+	.probe = kexec_zimage_probe,
+};
+
 const struct kexec_file_ops * const kexec_file_loaders[] = {
-	NULL
+	&kexec_zimage_ops,
 };