Le 21/08/2018 à 16:38, Ondrej Mosnáček a écrit :
ut 21. 8. 2018 o 16:18 Stephan Mueller [off-list ref] napísal(a):
quoted
Am Dienstag, 21. August 2018, 14:48:11 CEST schrieb Ondrej Mosnáček:
Hi Ondrej, Marcelo,
(+Marcelo)
quoted
Looking at crypto/algif_skcipher.c, I can see that skcipher_recvmsg()
holds the socket lock the whole time and yet passes
CRYPTO_TFM_REQ_MAY_SLEEP to the cipher implementation. Isn't that
wrong?
I think you are referring to lock_sock(sk)?
If so, this should not be the culprit: the socket lock is in essence a mutex-
like operation with its own wait queue that it allowed to sleep. In
lock_sock_nested that is called by lock_sock it even has the call of
might_sleep which indicates that the caller may be put to sleep.
Looking into the code (without too much debugging) I see in the function
p8_aes_cbc_encrypt that is part of the stack trace the call to
preempt_disable() which starts an atomic context. The preempt_enable() is
invoked after the walk operation.
The preempt_disable increases the preempt_count. That counter is used by
in_atomic() to check whether we are in atomic context.
The issue is that blkcipher_walk_done may call crypto_yield() which then
invokes cond_resched if the implementation is allowed to sleep.
Indeed, you're right, the issue is actually in the vmx_crypto code. I
remember having looked at the 'ctr(aes)' implementation in there a few
days ago (I think I was trying to debug this very issue, but for some
reason I only looked at ctr(aes)...) and I didn't find any bug, so
that's why I jumped to suspecting the algif_skcipher code... I should
have double-checked :)
It turns out the 'cbc(aes)' (and actually also 'xts(aes)')
implementation is coded a bit differently and they both *do* contain
the sleep-in-atomic bug. I will try to fix them according to the
correct CTR implementation and send a patch.
CC: linuxppc-dev@lists.ozlabs.org <redacted>
Thanks,
Ondrej
quoted
@Marcelo: shouldn't be the sleep flag be cleared when entering the
preempt_disable section?
Ciao
Stephan
CC: Paulo Flabiano Smorigo <redacted>
Yes, I do believe that CTR is doing it right. Preemption only needs to be
disabled during the aes_p8_cbc_encrypt() call, to avoid trashing the
VSX registers during the AES operation.
--
Regards,
Marcelo
On Tue, Aug 21, 2018 at 05:03:50PM +0200, Christophe LEROY wrote:
Le 21/08/2018 à 16:38, Ondrej Mosnáček a écrit :
quoted
ut 21. 8. 2018 o 16:18 Stephan Mueller [off-list ref] napísal(a):
quoted
Am Dienstag, 21. August 2018, 14:48:11 CEST schrieb Ondrej Mosnáček:
Hi Ondrej, Marcelo,
(+Marcelo)
quoted
Looking at crypto/algif_skcipher.c, I can see that skcipher_recvmsg()
holds the socket lock the whole time and yet passes
CRYPTO_TFM_REQ_MAY_SLEEP to the cipher implementation. Isn't that
wrong?
I think you are referring to lock_sock(sk)?
If so, this should not be the culprit: the socket lock is in essence a mutex-
like operation with its own wait queue that it allowed to sleep. In
lock_sock_nested that is called by lock_sock it even has the call of
might_sleep which indicates that the caller may be put to sleep.
Looking into the code (without too much debugging) I see in the function
p8_aes_cbc_encrypt that is part of the stack trace the call to
preempt_disable() which starts an atomic context. The preempt_enable() is
invoked after the walk operation.
The preempt_disable increases the preempt_count. That counter is used by
in_atomic() to check whether we are in atomic context.
The issue is that blkcipher_walk_done may call crypto_yield() which then
invokes cond_resched if the implementation is allowed to sleep.
Indeed, you're right, the issue is actually in the vmx_crypto code. I
remember having looked at the 'ctr(aes)' implementation in there a few
days ago (I think I was trying to debug this very issue, but for some
reason I only looked at ctr(aes)...) and I didn't find any bug, so
that's why I jumped to suspecting the algif_skcipher code... I should
have double-checked :)
It turns out the 'cbc(aes)' (and actually also 'xts(aes)')
implementation is coded a bit differently and they both *do* contain
the sleep-in-atomic bug. I will try to fix them according to the
correct CTR implementation and send a patch.
CC: linuxppc-dev@lists.ozlabs.org <redacted>
quoted
Thanks,
Ondrej
quoted
@Marcelo: shouldn't be the sleep flag be cleared when entering the
preempt_disable section?
Ciao
Stephan