[tip:x86/urgent] x86, boot: Skip relocs when load address unchanged

[tip-bot for Kees Cook]

Commit-ID:  f285f4a21c3253887caceed493089ece17579d59
Gitweb:     http://git.kernel.org/tip/f285f4a21c3253887caceed493089ece17579d59
Author:     Kees Cook <keescook@xxxxxxxxxxxx>
AuthorDate: Thu, 15 Jan 2015 16:51:46 -0800
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 20 Jan 2015 12:37:23 +0100

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@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Thomas D. <whissi@xxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Junjie Mao <eternal.n08@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20150116005146.GA4212@xxxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 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 dcc1c53..a950864 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;
 }
--
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