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author | Eric Biggers <ebiggers@google.com> | 2017-11-07 14:15:27 -0800 |
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committer | Herbert Xu <herbert@gondor.apana.org.au> | 2017-11-10 19:20:26 +0800 |
commit | 1d9ddde12e3c9bab7f3d3484eb9446315e3571ca (patch) | |
tree | b951622c25b368b0224012e2a463aee35c92d7da /crypto/Kconfig | |
parent | 63c53823f00f0ffd13e8c86b05c1486614a2df85 (diff) | |
download | op-kernel-dev-1d9ddde12e3c9bab7f3d3484eb9446315e3571ca.zip op-kernel-dev-1d9ddde12e3c9bab7f3d3484eb9446315e3571ca.tar.gz |
lib/mpi: call cond_resched() from mpi_powm() loop
On a non-preemptible kernel, if KEYCTL_DH_COMPUTE is called with the
largest permitted inputs (16384 bits), the kernel spends 10+ seconds
doing modular exponentiation in mpi_powm() without rescheduling. If all
threads do it, it locks up the system. Moreover, it can cause
rcu_sched-stall warnings.
Notwithstanding the insanity of doing this calculation in kernel mode
rather than in userspace, fix it by calling cond_resched() as each bit
from the exponent is processed. It's still noninterruptible, but at
least it's preemptible now.
Do the cond_resched() once per bit rather than once per MPI limb because
each limb might still easily take 100+ milliseconds on slow CPUs.
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto/Kconfig')
0 files changed, 0 insertions, 0 deletions