x86, boot: Skip relocs when load address unchanged

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>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20150116005146.GA4212@www.outflux.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 1 deletions

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index dcc1c536cc21..a950864a64da 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -373,6 +373,8 @@ asmlinkage __visible void *decompress_kernel(void *rmode, memptr heap,
                                   unsigned long output_len,
                                   unsigned long run_size)
 {
+        unsigned char *output_orig = output;
+
         real_mode = rmode;
 
         sanitize_boot_params(real_mode);
@@ -421,7 +423,12 @@ asmlinkage __visible 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 output;
 }