On Tue, Mar 22, 2016 at 12:32 AM, Baoquan He <b...@redhat.com> wrote:
> From: Yinghai Lu <ying...@kernel.org>
>
> Now new randomized output can only be chosen from regions above loaded
> address. In this case, for bootloaders like kexec which always loads
> kernel near the end of ram, it doesn't do randomization at all. Or kernel
> is loaded in a very big starting address, we should not give up that area
> is loaded in a very large address, then the area below the large loaded
> address will be given up. This is not reasonable.
>
> With correct tracking in mem_avoid we can allow random output below
> loaded address. With this change, though kexec can get random ouput
> below its loaded address of kernel.
>
> Now we just pick 512M as min_addr. If kernel loaded address is bigger than
> 512M, E.g 8G. Then [512M, 8G) can be added into random output candidate area.
>
> Signed-off-by: Yinghai Lu <ying...@kernel.org>
> ---
> arch/x86/boot/compressed/aslr.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
> index ddfc3d0..d072ca7 100644
> --- a/arch/x86/boot/compressed/aslr.c
> +++ b/arch/x86/boot/compressed/aslr.c
> @@ -446,7 +446,8 @@ void choose_kernel_location(unsigned char *input,
> unsigned long output_size,
> unsigned char **virt_offset)
> {
> - unsigned long random;
> + unsigned long random, min_addr;
> +
> *virt_offset = (unsigned char *)LOAD_PHYSICAL_ADDR;
>
> #ifdef CONFIG_HIBERNATION
> @@ -467,8 +468,13 @@ void choose_kernel_location(unsigned char *input,
> mem_avoid_init((unsigned long)input, input_size,
> (unsigned long)*output);
>
> + /* start from 512M */
> + min_addr = (unsigned long)*output;
> + if (min_addr > (512UL<<20))
> + min_addr = 512UL<<20;
The goal is to find a minimum address? I'm not sure this comment makes
sense. Shouldn't this be:
/* Lower minimum to 512M. */
min_addr = min_t(unsigned long, *output, 512UL << 20);
Or something like that?
> +
> /* Walk e820 and find a random address. */
> - random = find_random_phy_addr((unsigned long)*output, output_size);
> + random = find_random_phy_addr(min_addr, output_size);
> if (!random)
> debug_putstr("KASLR could not find suitable E820
> region...\n");
> else {
> --
> 2.5.0
>
-Kees
--
Kees Cook
Chrome OS & Brillo Security
