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Message-ID: <57AC9C43.5080106@intel.com>
Date: Thu, 11 Aug 2016 08:39:47 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Emese Revfy <re.emese@...il.com>, Andrew Morton <akpm@...ux-foundation.org>,
Jonathan Corbet <corbet@....net>, Vlastimil Babka <vbabka@...e.cz>,
Mel Gorman <mgorman@...hsingularity.net>, Michal Hocko <mhocko@...e.com>,
Johannes Weiner <hannes@...xchg.org>, Joonsoo Kim <iamjoonsoo.kim@....com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Taku Izumi <izumi.taku@...fujitsu.com>, linux-doc@...r.kernel.org,
linux-mm@...ck.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] mm: Add the ram_latent_entropy kernel parameter
On 08/10/2016 03:28 PM, Kees Cook wrote:
> + if (ram_latent_entropy && !PageHighMem(page) &&
> + page_to_pfn(page) < 0x100000) {
> + u64 hash = 0;
> + size_t index, end = PAGE_SIZE * nr_pages / sizeof(hash);
> + const u64 *data = lowmem_page_address(page);
> +
> + for (index = 0; index < end; index++)
> + hash ^= hash + data[index];
> + add_device_randomness((const void *)&hash, sizeof(hash));
> + }
When I was first reading this, I thought it was using the _addresses_ of
the freed memory for entropy. But it's actually using the _contents_.
The description could probably use a wee bit of sprucing up.
It might also be nice to say in the patch description (and the
Documentation/) what you expect to be in this memory. It will obviously
be zeros for the vast majority of the space, but I do wonder what else
ends up in there in practice.
Why is it limited to 4GB? Just so it doesn't go and try to XOR the
contents of a multi-TB system if it got turned on there? :)
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