linux-kernel - Re: [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size

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Date:   Wed, 29 Aug 2018 14:49:40 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Baoquan He <bhe@...hat.com>
Cc:     tglx@...utronix.de, mingo@...nel.org, hpa@...or.com,
        thgarnie@...gle.com, kirill.shutemov@...ux.intel.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr
 region initial size

On Wed, Aug 29, 2018 at 10:17:53AM +0800, Baoquan He wrote:
> In memory KASLR, __PHYSICAL_MASK_SHIFT is taken to calculate the
> initial size of the direct mapping region. This is right in the
> old code where __PHYSICAL_MASK_SHIFT was equal to MAX_PHYSMEM_BITS,
> 46bit, and only 4-level mode was supported.
> 
> Later, in commit:
> b83ce5ee91471d ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52"),
> __PHYSICAL_MASK_SHIFT was changed to be 52 always, no matter it's
> 5-level or 4-level. This is wrong for 4-level paging. Then when
> adapt phyiscal memory region size based on available memory, it
> will overflow if the amount of system RAM and the padding is bigger
> than 64TB.
> 
> In fact, here MAX_PHYSMEM_BITS should be used instead. Fix it by
> by replacing __PHYSICAL_MASK_SHIFT with MAX_PHYSMEM_BITS.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov