From: Dave Hansen <dave.hansen@intel.com>
To: Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Emese Revfy <re.emese@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jonathan Corbet <corbet@lwn.net>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Taku Izumi <izumi.taku@jp.fujitsu.com>,
linux-doc@vger.kernel.org, linux-mm@kvack.org,
kernel-hardening@lists.openwall.com
Subject: [kernel-hardening] Re: [PATCH] mm: Add the ram_latent_entropy kernel parameter
Date: Thu, 11 Aug 2016 08:39:47 -0700 [thread overview]
Message-ID: <57AC9C43.5080106@intel.com> (raw)
In-Reply-To: <20160810222805.GA13733@www.outflux.net>
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? :)
WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave.hansen@intel.com>
To: Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Emese Revfy <re.emese@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jonathan Corbet <corbet@lwn.net>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Taku Izumi <izumi.taku@jp.fujitsu.com>,
linux-doc@vger.kernel.org, linux-mm@kvack.org,
kernel-hardening@lists.openwall.com
Subject: Re: [PATCH] mm: Add the ram_latent_entropy kernel parameter
Date: Thu, 11 Aug 2016 08:39:47 -0700 [thread overview]
Message-ID: <57AC9C43.5080106@intel.com> (raw)
In-Reply-To: <20160810222805.GA13733@www.outflux.net>
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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WARNING: multiple messages have this Message-ID (diff)
From: Dave Hansen <dave.hansen@intel.com>
To: Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Emese Revfy <re.emese@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jonathan Corbet <corbet@lwn.net>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Taku Izumi <izumi.taku@jp.fujitsu.com>,
linux-doc@vger.kernel.org, linux-mm@kvack.org,
kernel-hardening@lists.openwall.com
Subject: Re: [PATCH] mm: Add the ram_latent_entropy kernel parameter
Date: Thu, 11 Aug 2016 08:39:47 -0700 [thread overview]
Message-ID: <57AC9C43.5080106@intel.com> (raw)
In-Reply-To: <20160810222805.GA13733@www.outflux.net>
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? :)
next prev parent reply other threads:[~2016-08-11 15:39 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-10 22:28 [kernel-hardening] [PATCH] mm: Add the ram_latent_entropy kernel parameter Kees Cook
2016-08-10 22:28 ` Kees Cook
2016-08-10 22:28 ` Kees Cook
2016-08-11 15:39 ` Dave Hansen [this message]
2016-08-11 15:39 ` Dave Hansen
2016-08-11 15:39 ` Dave Hansen
2016-08-12 3:52 ` [kernel-hardening] " Balbir Singh
2016-08-12 3:52 ` Balbir Singh
2016-08-12 3:52 ` Balbir Singh
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