On 04/26/17 at 06:39pm, Baoquan He wrote:
> Dave found when kdump kernel will reset to bios immediately if kaslr
^~ this 'when' is redundent, sorry
> is enabled and physical randomization failed to faind a new position
> for kernel. But nokaslr works in this case.
>
> The reason is kaslr will install a new page table for ident mapping,
> while it missed to consider building ident mapping for original area
> of kernel if kaslr failed on physical randomization.
>
> In fact bootloaders including kexec/kdump have built ident mapping
> for original place of kernel. We can only install new ident mapping
> page table when physical kaslr succeeds. Otherwise we just keep the
> old page table unchanged just like nokaslr does.
>
> Signed-off-by: Baoquan He <[email protected]>
> Signed-off-by: Dave Young <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: [email protected]
> Cc: Kees Cook <[email protected]>
> Cc: Yinghai Lu <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Dave Jiang <[email protected]>
> Cc: Thomas Garnier <[email protected]>
> ---
> arch/x86/boot/compressed/kaslr.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c
> b/arch/x86/boot/compressed/kaslr.c
> index e5eb0c3..7a8b443 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -650,10 +650,16 @@ void choose_random_location(unsigned long input,
> add_identity_map(random_addr, output_size);
> *output = random_addr;
> }
> +
> + /*
> + * This actually loads the identity pagetable on x86_64.
> + * And this should only be done only if a new position
> + * is found. Otherwise we should keep the old page table
> + * to make it be like nokaslr case.
> + */
> + finalize_identity_maps();
> }
>
> - /* This actually loads the identity pagetable on x86_64. */
> - finalize_identity_maps();
>
> /* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
> if (IS_ENABLED(CONFIG_X86_64))
> --
> 2.5.5
>
