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Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization

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On Mon, Aug 08, 2016 at 11:40:07AM -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.

Can't this number of required pages be computed based on the
randomization offset or somesuch instead of maxing it out by default on
every machine which enables CONFIG_RANDOMIZE_MEMORY?

> This bug was found while doing extensive testing of KASLR memory
> randomization on different type of hardware.
> 
> Signed-off-by: Thomas Garnier <thgarnie@google.com>
> ---
> Based on next-20160805
> ---
>  arch/x86/mm/init.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 6209289..3a27e6a 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -130,6 +130,14 @@ void  __init early_alloc_pgt_buf(void)
>  	unsigned long tables = INIT_PGT_BUF_SIZE;
>  	phys_addr_t base;
>  
> +	/*
> +	 * Depending on the machine e860 memory layout and the PUD alignement.

				    e820			   alignment

> +	 * We may need twice more pages when KASLR memoy randomization is

						  memory

> +	 * enabled.
> +	 */
> +	if (IS_ENABLED(CONFIG_RANDOMIZE_MEMORY))
> +		tables *= 2;
> +
>  	base = __pa(extend_brk(tables, PAGE_SIZE));
>  
>  	pgt_buf_start = base >> PAGE_SHIFT;
> -- 
> 2.8.0.rc3.226.g39d4020
> 

-- 
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)
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[PATCH v1 1/2] x86/KASLR: Fix physical memory calculation on KASLR memory randomization Thomas Garnier <thgarnie@google.com> - 2016-08-08 20:50 +0200
  [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization Thomas Garnier <thgarnie@google.com> - 2016-08-08 20:50 +0200
    Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory  randomization Borislav Petkov <bp@suse.de> - 2016-08-09 06:10 +0200
      Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization "H. Peter Anvin" <hpa@zytor.com> - 2016-08-09 06:20 +0200
    Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization Thomas Garnier <thgarnie@google.com> - 2016-08-09 17:00 +0200
  Re: [PATCH v1 1/2] x86/KASLR: Fix physical memory calculation on  KASLR memory randomization Joerg Roedel <jroedel@suse.de> - 2016-08-09 18:10 +0200
    Re: [PATCH v1 1/2] x86/KASLR: Fix physical memory calculation on  KASLR memory randomization Thomas Garnier <thgarnie@google.com> - 2016-08-09 18:40 +0200
  Re: [PATCH v1 1/2] x86/KASLR: Fix physical memory calculation on  KASLR memory randomization Thomas Garnier <thgarnie@google.com> - 2016-08-09 18:10 +0200

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