[tip:x86/microcode] x86/microcode: Look for the initrd at the correct address on 32-bit

[tip-bot for Borislav Petkov <tipbot@zytor.com>]

Commit-ID:  a3d98c9358e3be28282ff60dcca01dbc9f402f30
Gitweb:     http://git.kernel.org/tip/a3d98c9358e3be28282ff60dcca01dbc9f402f30
Author:     Borislav Petkov <bp@suse.de>
AuthorDate: Wed, 14 Jun 2017 16:06:25 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Jun 2017 12:54:24 +0200

x86/microcode: Look for the initrd at the correct address on 32-bit

Early during boot, the BSP finds the ramdisk's position from boot_params
but by the time the APs get to boot, the BSP has continued in the mean
time and has potentially managed to relocate that ramdisk.

And in that case, the APs need to find the ramdisk at its new position,
in *physical* memory as they're running before paging has been enabled.

Thus, get the updated physical location of the ramdisk which is in the
relocated_ramdisk variable.

Signed-off-by: Borislav Petkov <bp@suse.de>
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/20170614140626.4462-1-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/cpu/microcode/core.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index e53d3c9..9cb98ee 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -290,6 +290,17 @@ struct cpio_data find_microcode_in_initrd(const char *path, bool use_pa)
 			return (struct cpio_data){ NULL, 0, "" };
 		if (initrd_start)
 			start = initrd_start;
+	} else {
+		/*
+		 * The picture with physical addresses is a bit different: we
+		 * need to get the *physical* address to which the ramdisk was
+		 * relocated, i.e., relocated_ramdisk (not initrd_start) and
+		 * since we're running from physical addresses, we need to access
+		 * relocated_ramdisk through its *physical* address too.
+		 */
+		u64 *rr = (u64 *)__pa_nodebug(&relocated_ramdisk);
+		if (*rr)
+			start = *rr;
 	}
 
 	return find_cpio_data(path, (void *)start, size, NULL);