Re: [PATCH v2 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization

[Borislav Petkov <bp@suse.de>]

On Tue, Aug 09, 2016 at 09:35:54AM -0700, Thomas Garnier wrote:
> Default implementation expects 6 pages maximum are needed for low page
> allocations. If KASLR memory randomization is enabled, the worse case
> of e820 layout would require 12 pages (no large pages). It is due to the
> PUD level randomization and the variable e820 memory layout.
> 
> This bug was found while doing extensive testing of KASLR memory
> randomization on different type of hardware.
> 
> Fixes: 021182e52fe0 ("Enable KASLR for physical mapping memory regions")
> Signed-off-by: Thomas Garnier <thgarnie@google.com>
> ---
> Based on next-20160805
> ---
>  arch/x86/mm/init.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 6209289..796e7af 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -122,8 +122,18 @@ __ref void *alloc_low_pages(unsigned int num)
>  	return __va(pfn << PAGE_SHIFT);
>  }
>  
> -/* need 3 4k for initial PMD_SIZE,  3 4k for 0-ISA_END_ADDRESS */
> -#define INIT_PGT_BUF_SIZE	(6 * PAGE_SIZE)
> +/*
> + * By default need 3 4k for initial PMD_SIZE,  3 4k for 0-ISA_END_ADDRESS.
> + * With KASLR memory randomization, depending on the machine e860 memory layout
> + * and the PUD alignement. We may need twice more pages when KASLR memoy
> + * randomization is enabled.

Can you please integrate all review feedback before you send your next
versions?

There's no "e860" thing and
s/memoy/memory/ and
s/alignement/alignment/

IOW, just integrate a spellchecker into your workflow.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--