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    Subject[PATCH 6/6] x86/boot: Correctly bounds-check relocations
    Date
    From: Yinghai Lu <yinghai@kernel.org>

    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>
    Cc: Baoquan He <bhe@redhat.com>
    [kees: rewrote changelog]
    Signed-off-by: Kees Cook <keescook@chromium.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 adef26d22224..75f2233b8414 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 bee6238e7cfc..8f0253d8c7ff 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
    --
    2.6.3
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