[PATCH v4 0/3] Secure prandom_u32 invocations

[david.keisarschm@mail.huji.ac.il]

From: David Keisar Schmidt <david.keisarschm@mail.huji.ac.il>

Hi,

The security improvements for prandom_u32 done in commits c51f8f88d705
from October 2020 and d4150779e60f from May 2022 didn't handle the cases
when prandom_bytes_state() and prandom_u32_state() are used.

Specifically, this weak randomization takes place in three cases:
    1.	mm/slab.c
    2.	mm/slab_common.c
    3.	arch/x86/mm/kaslr.c

The first two invocations (mm/slab.c, mm/slab_common.c) are used to create
randomization in the slab allocator freelists.
This is done to make sure attackers can’t obtain information on the heap state.

The last invocation, inside arch/x86/mm/kaslr.c,
randomizes the virtual address space of kernel memory regions.
The use of prandom_bytes_state() is justified since it has a dedicated
state and draws only 3 pseudo random values, but the seeding state takes advantage
of only 32 bits out of 64 bits of the seed.
Hence, we have added the necessary changes to make those randomizations stronger,
switching the invocation of prandom_seed_state to a more secure version, which
we implemented inside kaslr.c.
---
Changes since v3:
* arch/x86/mm/kaslr.c: secure the way the region offsets are generated in the
  seeding state - Adding a revised version of prandom_seed_state
* edited commit messages

Changes since v2:
* edited commit message.
* replaced instances of get_random_u32 with get_random_u32_below
      in mm/slab.c, mm/slab_common.c

Regards,

David Keisar Schmidt (3):
  Replace invocation of weak PRNG in mm/slab.c
  Replace invocation of weak PRNG inside mm/slab_common.c
  Add 64bits prandom_seed_state to arch/x86/mm/kaslr.c

 arch/x86/mm/kaslr.c | 26 +++++++++++++++++++++++++-
 mm/slab.c           | 25 ++++++++++---------------
 mm/slab_common.c    | 11 +++--------
 3 files changed, 38 insertions(+), 24 deletions(-)

-- 
2.38.0