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Date: Tue, 9 Aug 2016 08:16:46 +0300
From: Mika Penttilä <mika.penttila@...tfour.com>
To: Thomas Garnier <thgarnie@...gle.com>, Thomas Gleixner
<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin"
<hpa@...or.com>, Borislav Petkov <bp@...e.de>, Joerg Roedel
<jroedel@...e.de>, Dave Young <dyoung@...hat.com>, "Rafael J . Wysocki"
<rafael.j.wysocki@...el.com>, Lv Zheng <lv.zheng@...el.com>, Baoquan He
<bhe@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Mark Salter
<msalter@...hat.com>, Aleksey Makarov <aleksey.makarov@...aro.org>, Kees Cook
<keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, Christian
Borntraeger <borntraeger@...ibm.com>, Fabian Frederick <fabf@...net.be>,
Toshi Kani <toshi.kani@...com>, Dan Williams <dan.j.williams@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v1 2/2] x86/KASLR: Increase BRK pages for KASLR memory
randomization
On 08/08/2016 09:40 PM, 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.
>
> Signed-off-by: Thomas Garnier <thgarnie@...gle.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.
> + * We may need twice more pages when KASLR memoy randomization is
> + * enabled.
> + */
> + if (IS_ENABLED(CONFIG_RANDOMIZE_MEMORY))
> + tables *= 2;
> +
> base = __pa(extend_brk(tables, PAGE_SIZE));
>
> pgt_buf_start = base >> PAGE_SHIFT;
>
You should increase the reserve also :
RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE);
--Mika
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