x86/microcode: Fix loading precedence

So it can happen that even with builtin microcode,
CONFIG_BLK_DEV_INITRD=y gets forgotten enabled.

Or, even with that disabled, an initrd image gets supplied by the boot
loader, by omission or is simply forgotten there. And since we do look
at boot_params.hdr.ramdisk_* to know whether we have received an initrd,
we might get puzzled.

So let's just make the loader look for builtin microcode first and if
found, ignore the ramdisk image.

If no builtin found, it falls back to scanning the supplied initrd, of
course.

For that, we move all the initrd scanning in a separate
__scan_microcode_initrd() function and fall back to it only if
load_builtin_intel_microcode() has failed.

Reported-and-tested-by: Gabriel Craciunescu <nix.or.die@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1465225850-7352-2-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 16 insertions, 12 deletions

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 8581963894c7..11dd1cc8e444 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -61,19 +61,20 @@ static u16 this_equiv_id;
 
 static struct cpio_data ucode_cpio;
 
-/*
- * Microcode patch container file is prepended to the initrd in cpio format.
- * See Documentation/x86/early-microcode.txt
- */
-static __initdata char ucode_path[] = "kernel/x86/microcode/AuthenticAMD.bin";
-
 static struct cpio_data __init find_ucode_in_initrd(void)
 {
+#ifdef CONFIG_BLK_DEV_INITRD
 	long offset = 0;
 	char *path;
 	void *start;
 	size_t size;
 
+	/*
+	 * Microcode patch container file is prepended to the initrd in cpio
+	 * format. See Documentation/x86/early-microcode.txt
+	 */
+	static __initdata char ucode_path[] = "kernel/x86/microcode/AuthenticAMD.bin";
+
 #ifdef CONFIG_X86_32
 	struct boot_params *p;
 
@@ -89,9 +90,12 @@ static struct cpio_data __init find_ucode_in_initrd(void)
 	path    = ucode_path;
 	start   = (void *)(boot_params.hdr.ramdisk_image + PAGE_OFFSET);
 	size    = boot_params.hdr.ramdisk_size;
-#endif
+#endif /* !CONFIG_X86_32 */
 
 	return find_cpio_data(path, start, size, &offset);
+#else
+	return (struct cpio_data){ NULL, 0, "" };
+#endif
 }
 
 static size_t compute_container_size(u8 *data, u32 total_size)
@@ -289,11 +293,11 @@ void __init load_ucode_amd_bsp(unsigned int family)
 	size = &ucode_cpio.size;
 #endif
 
-	cp = find_ucode_in_initrd();
-	if (!cp.data) {
-		if (!load_builtin_amd_microcode(&cp, family))
-			return;
-	}
+	if (!load_builtin_amd_microcode(&cp, family))
+		cp = find_ucode_in_initrd();
+
+	if (!(cp.data && cp.size))
+		return;
 
 	*data = cp.data;
 	*size = cp.size;