Re: [Tails-dev] PROBLEM: memtest tests only LOWMEM

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Author: Chris
Date:  
To: The Tails public development discussion list
Subject: Re: [Tails-dev] PROBLEM: memtest tests only LOWMEM
Is this still an issue? My understanding is that there is a maximum of
about 2 minutes before all contents of memory have "dissipated". How long
does it take to 'wipe' the memory? The 2nd question is what do you call
wiping? Doing more than one pass is probably no more effective than a
single pass.

> 1. On 32-bit x86, memtest=n tests only LOWMEM memory (~ 895 MiB),
> HIGHMEM is ignored
>
> 2. On 3.0.4-hardened-r5, HIGHMEM memory (HIGHMEM64G in my tests) is
> apparently ignored during memtest. Looking at arch/x86/mm/memtest.c,
> no special mapping is performed (kmap/kunmap?), so it seems that at
> most ~895 MiB can be tested in 32-bit x86 kernels. This might not
> appear like an important issue (as there are other memory testing
> tools available), but memtest is extremely useful for anti-forensic
> memory wiping on shutdown/reboot in security-oriented distributions
> like Liberté Linux and Tails, and there is no other good substitute.
> See, for instance, some background in Debian bug
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=646361.
>
> 3. Keywords: memtest, highmem, mm, security
>
> 4. Kernel version: 3.0.4-hardened-r5 (Gentoo) x86 32-bit with PAE
>
> --
> Maxim Kammerer
> Liberté Linux (discussion / support: http://dee.su/liberte-contribute)
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