linux-kernel - [PATCH 3.12 158/176] x86, boot: Skip relocs when load address unchanged

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Date:	Wed, 28 Jan 2015 15:29:48 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Jan Beulich <JBeulich@...e.com>,
	Junjie Mao <eternal.n08@...il.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 158/176] x86, boot: Skip relocs when load address unchanged

From: Kees Cook <keescook@...omium.org>

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

===============

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@...hat.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Tested-by: Thomas D. <whissi@...ssi.de>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Jan Beulich <JBeulich@...e.com>
Cc: Junjie Mao <eternal.n08@...il.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Link: http://lkml.kernel.org/r/20150116005146.GA4212@www.outflux.net
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 434f077d2c4d..1b05afd8cd7f 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;
 }
-- 
2.2.2

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