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23d1aee92b
Here is a rework of the generate_entropy function of the pseudo random device driver exploiting the prno CPACF instruction. George Spelvin pointed out some issues with the existing implementation. One point was, that the buffer used to store the stckf values is 2 pages which are initially filled with get_random_bytes() for each 64 byte junk produced by the function. Another point was that the stckf values only carry entropy in the LSB and thus a buffer of 2 pages is not really needed. Then there was a comment about the use of the kimd cpacf function without proper initialization. The rework addresses these points and now one page is used and only one half of this is filled with get_random_bytes() on each chunk of 64 bytes requested data. The other half of the page is filled with stckf values exored into with an overlap of 4 bytes. This can be done due to the fact that only the lower 4 bytes carry entropy we need. For more details about the algorithm used, see the header of the function. The generate_entropy() function now uses the cpacf function klmd with proper initialization of the parameter block to perform the sha512 hash. George also pointed out some issues with the internal buffers used for seeding and reads. These buffers are now zeroed with memzero_implicit after use. Signed-off-by: Harald Freudenberger <freude@linux.ibm.com> Reported-by: George Spelvin <lkml@sdf.org> Suggested-by: George Spelvin <lkml@sdf.org> Reviewed-by: Patrick Steuer <steuer@linux.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.