linux-kernel - [PATCH] x86, kaslr: handle Gold linker for finding bss+brk

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Message-ID: <20141118001604.GA25045@www.outflux.net>
Date:	Mon, 17 Nov 2014 16:16:04 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...hat.com>
Cc:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Junjie Mao <eternal.n08@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] x86, kaslr: handle Gold linker for finding bss+brk

When building with the Gold linker, the .bss and .brk areas of vmlinux
are shown as consecutive instead of having the same file offset. Allow
for either state, as long as things add up correctly.

Fixes: e6023367d779 ("x86, kaslr: Prevent .bss from overlaping initrd")
Reported-by: Markus Trippelsdorf <markus@...ppelsdorf.de>
Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: Junjie Mao <eternal.n08@...il.com>
---
 arch/x86/tools/calc_run_size.pl | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/tools/calc_run_size.pl b/arch/x86/tools/calc_run_size.pl
index 0b0b124d3ece..23210baade2d 100644
--- a/arch/x86/tools/calc_run_size.pl
+++ b/arch/x86/tools/calc_run_size.pl
@@ -19,7 +19,16 @@ while (<>) {
 		if ($file_offset == 0) {
 			$file_offset = $offset;
 		} elsif ($file_offset != $offset) {
-			die ".bss and .brk lack common file offset\n";
+			# BFD linker shows the same file offset in ELF.
+			# Gold linker shows them as consecutive.
+			next if ($file_offset + $mem_size == $offset + $size);
+
+			printf STDERR "file_offset: 0x%lx\n", $file_offset;
+			printf STDERR "mem_size: 0x%lx\n", $mem_size;
+			printf STDERR "offset: 0x%lx\n", $offset;
+			printf STDERR "size: 0x%lx\n", $size;
+
+			die ".bss and .brk are non-contiguous\n";
 		}
 	}
 }
-- 
1.9.1


-- 
Kees Cook
Chrome OS Security
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