[PATCH 3.13.y-ckt 094/103] x86, boot: Skip relocs when load address unchanged

[Kamal Mostafa]

3.13.11-ckt16 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook at chromium.org>

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