[Tails-dev] PROBLEM: memtest tests only LOWMEM

Maxim Kammerer mk at dee.su
Mon Dec 26 03:18:29 CET 2011

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

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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