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

Kamal Mostafa
2015-02-19T00:35:58Z

From: Kees Cook <keescook@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@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Thomas D. <whissi@whissi.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Junjie Mao <eternal.n08@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/20150116005146.GA4212@www.outflux.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kamal Mostafa <kamal@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