[3.13.y-ckt stable] Patch "x86, boot: Skip relocs when load address unchanged" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86, boot: Skip relocs when load address unchanged

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From dac1923a90dfe4e6289d279f70fd6765dae35336 Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook at chromium.org>
Date: Thu, 15 Jan 2015 16:51:46 -0800
Subject: x86, boot: Skip relocs when load address unchanged

commit f285f4a21c3253887caceed493089ece17579d59 upstream.

On 64-bit, relocation is not required unless the load address gets
changed. Without this, relocations do unexpected things when the kernel
is above 4G.

Reported-by: Baoquan He <bhe at redhat.com>
Signed-off-by: Kees Cook <keescook at chromium.org>
Tested-by: Thomas D. <whissi at whissi.de>
Cc: Vivek Goyal <vgoyal at redhat.com>
Cc: Jan Beulich <JBeulich at suse.com>
Cc: Junjie Mao <eternal.n08 at gmail.com>
Cc: Andi Kleen <ak at linux.intel.com>
Link: http://lkml.kernel.org/r/20150116005146.GA4212@www.outflux.net
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/boot/compressed/misc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 434f077..1b05afd 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -401,6 +401,8 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap,
 				  unsigned char *output,
 				  unsigned long output_len)
 {
+	unsigned char *output_orig = output;
+
 	real_mode = rmode;

 	sanitize_boot_params(real_mode);
@@ -439,7 +441,12 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap,
 	debug_putstr("\nDecompressing Linux... ");
 	decompress(input_data, input_len, NULL, NULL, output, NULL, error);
 	parse_elf(output);
-	handle_relocations(output, output_len);
+	/*
+	 * 32-bit always performs relocations. 64-bit relocations are only
+	 * needed if kASLR has chosen a different load address.
+	 */
+	if (!IS_ENABLED(CONFIG_X86_64) || output != output_orig)
+		handle_relocations(output, output_len);
 	debug_putstr("done.\nBooting the kernel.\n");
 	return;
 }
--
1.9.1