PROBLEM: memtest tests only LOWMEM

PROBLEM: memtest tests only LOWMEM

[Maxim Kammerer]

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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Re: PROBLEM: memtest tests only LOWMEM

[Maxim Kammerer]

Hi,

There have been no reply in two weeks. Does it mean that this is the
wrong mailing list for this bug? Or that there is no interest in
fixing it?

Thanks,
Maxim

On Mon, Dec 26, 2011 at 04:18, Maxim Kammerer <mk@dee.su> wrote:
> 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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