mainlining shenanigans
5c3b747ef5
Before, the first 64 bytes of input, regardless of how entropic it was, would be used to mutate the crng base key directly, and none of those bytes would be credited as having entropy. Then 256 bits of credited input would be accumulated, and only then would the rng transition from the earlier "fast init" phase into being actually initialized. The thinking was that by mixing and matching fast init and real init, an attacker who compromised the fast init state, considered easy to do given how little entropy might be in those first 64 bytes, would then be able to bruteforce bits from the actual initialization. By keeping these separate, bruteforcing became impossible. However, by not crediting potentially creditable bits from those first 64 bytes of input, we delay initialization, and actually make the problem worse, because it means the user is drawing worse random numbers for a longer period of time. Instead, we can take the first 128 bits as fast init, and allow them to be credited, and then hold off on the next 128 bits until they've accumulated. This is still a wide enough margin to prevent bruteforcing the rng state, while still initializing much faster. Then, rather than trying to piecemeal inject into the base crng key at various points, instead just extract from the pool when we need it, for the crng_init==0 phase. Performance may even be better for the various inputs here, since there are likely more calls to mix_pool_bytes() then there are to get_random_bytes() during this phase of system execution. Since the preinit injection code is gone, bootloader randomness can then do something significantly more straight forward, removing the weird system_wq hack in hwgenerator randomness. Cc: Theodore Ts'o <tytso@mit.edu> Cc: Dominik Brodowski <linux@dominikbrodowski.net> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.