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    Subject[PATCH 3.18 41/61] x86, boot: Skip relocs when load address unchanged
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Kees Cook <keescook@chromium.org>

    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@redhat.com>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Tested-by: Thomas D. <whissi@whissi.de>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Cc: Jan Beulich <JBeulich@suse.com>
    Cc: Junjie Mao <eternal.n08@gmail.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Link: http://lkml.kernel.org/r/20150116005146.GA4212@www.outflux.net
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/boot/compressed/misc.c | 9 ++++++++-
    1 file changed, 8 insertions(+), 1 deletion(-)

    --- a/arch/x86/boot/compressed/misc.c
    +++ b/arch/x86/boot/compressed/misc.c
    @@ -361,6 +361,8 @@ asmlinkage __visible void *decompress_ke
    unsigned long output_len,
    unsigned long run_size)
    {
    + unsigned char *output_orig = output;
    +
    real_mode = rmode;

    sanitize_boot_params(real_mode);
    @@ -409,7 +411,12 @@ asmlinkage __visible void *decompress_ke
    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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