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Subject[tip:x86/boot] x86/boot: Correctly bounds-check relocations
Commit-ID:  4abf061bf87bbd856c8d60199b2fba8b8f9b9fd6
Gitweb: http://git.kernel.org/tip/4abf061bf87bbd856c8d60199b2fba8b8f9b9fd6
Author: Yinghai Lu <yinghai@kernel.org>
AuthorDate: Thu, 28 Apr 2016 17:09:08 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 29 Apr 2016 11:03:30 +0200

x86/boot: Correctly bounds-check relocations

Relocation handling performs bounds checking on the resulting calculated
addresses. The existing code uses output_len (VO size plus relocs size) as
the max address. This is not right since the max_addr check should stop at
the end of VO and exclude bss, brk, etc, which follows. The valid range
should be VO [_text, __bss_start] in the loaded physical address space.

This patch adds an export for __bss_start in voffset.h and uses it to
set the correct limit for max_addr.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
[ Rewrote the changelog. ]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: lasse.collin@tukaani.org
Link: http://lkml.kernel.org/r/1461888548-32439-7-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/boot/compressed/Makefile | 2 +-
arch/x86/boot/compressed/misc.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index adef26d..75f2233 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -57,7 +57,7 @@ LDFLAGS_vmlinux := -T
hostprogs-y := mkpiggy
HOST_EXTRACFLAGS += -I$(srctree)/tools/include

-sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(_text\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p'
+sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(_text\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p'

quiet_cmd_voffset = VOFFSET $@
cmd_voffset = $(NM) $< | sed -n $(sed-voffset) > $@
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index bee6238..8f0253d 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -191,7 +191,7 @@ static void handle_relocations(void *output, unsigned long output_len)
int *reloc;
unsigned long delta, map, ptr;
unsigned long min_addr = (unsigned long)output;
- unsigned long max_addr = min_addr + output_len;
+ unsigned long max_addr = min_addr + (VO___bss_start - VO__text);

/*
* Calculate the delta between where vmlinux was linked to load
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