Move from sdmem to memtest

Rationale

Replace sdmem with the Linux kernel’s memtest=2 feature will fix sdmem does not clear all memory and will generally be simpler and more robust.

Update: according to Liberte Linux’ Maxim Kammerer, the memtest= approach is flawed; it only tests LOWMEM, "so it seems that at most ~895 MiB can be tested in 32-bit x86 kernels". Therefore, it’s currently not fit for any kind of anti-forensics memory wiping. Being discussed on tails-dev / reported upstream, end of 2011: from sdmem to memtest, and testing procedures, PROBLEM: memtest tests only LOWMEM. Max Kammerer opened Linux bug 42630.

Let’s wait for the outcome of the discussion with upstream.

There has been basically no progress 3 months later. We probably have to find an interested kernel hacker to patch the "memtest" code for our usecase.

Plans

Implemented in bugfix/from_sdmem_to_memtest branch.

Let’s wait for feature/hugetlb_mem_wipe to be merged. If we’re happy with it, we can avoid moving to memtest.

Related issues

• Related to #5762 (closed)
• Blocked by #5342 (closed)

Original created by @tails on 5658 (Redmine)