On 01/15/15 at 04:51pm, Kees Cook wrote:
> 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.
This patch works for me. And good to see it's being merged. About the
patch log, I would say relocations do unexpected things when the kernel
is above 1G since randomization is done from 16M to 1G, namely
CONFIG_RANDOMIZE_BASE_MAX_OFFSET. So above 1G kernel text mapping will
step into kernel module mapping region.
BTW, I am working on separate randomization of kernel physical and virtual
address , will post it. But it won't conflict with this because I don't
think it can be accepted in a short time. Before that this patch truly
fix the kexec/kdump bug when kaslr is compiled in.
Thanks
Baoquan
>
> Reported-by: Baoquan He <b...@redhat.com>
> Signed-off-by: Kees Cook <keesc...@chromium.org>
> Cc: sta...@vger.kernel.org
> ---
> This is a reimplementation of Baoquan's "kaslr: check if kernel location is
> changed", which performs the check without needing to change the function
> declaration. This should have exactly the same effect, but I dropped Vivek's
> Ack and Thomas's Test, since it's technically a different patch.
> ---
> 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 dcc1c536cc21..a950864a64da 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -373,6 +373,8 @@ asmlinkage __visible void *decompress_kernel(void *rmode,
> memptr heap,
> unsigned long output_len,
> unsigned long run_size)
> {
> + unsigned char *output_orig = output;
> +
> real_mode = rmode;
>
> sanitize_boot_params(real_mode);
> @@ -421,7 +423,12 @@ asmlinkage __visible 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 output;
> }
> --
> 1.9.1
>
>
> --
> Kees Cook
> Chrome OS Security
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