Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 30 Sep 2019 22:11:33 +0200 | Subject | Re: [PATCH 2/3] crypto: inside-secure - Reduce stack usage |
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On Mon, Sep 30, 2019 at 9:04 PM Pascal Van Leeuwen <pvanleeuwen@verimatrix.com> wrote:
> > Alternatively, it should be possible to shrink these allocations > > as the extra buffers appear to be largely unnecessary, but doing > > this would be a much more invasive change. > > > Actually, for HMAC-SHA512 you DO need all that buffer space. > You could shrink it to 2 * ctx->state_sz but then your simple indexing > is no longer going to fly. Not sure if that would be worth the effort.
Stack allocations can no longer be dynamically sized in the kernel, so that would not work.
What I noticed though is that the largest part of safexcel_ahash_export_state is used in the 'cache' member, and this is apparently only referenced inside of safexcel_hmac_init_iv, which you call twice. If that cache can be allocated only once, you save SHA512_BLOCK_SIZE bytes in one of the two paths.
> I don't like the part where you dynamically allocate the cryto_aes_ctx > though, I think that was not necessary considering its a lot smaller.
I count 484 bytes for it, which is really large.
> And it conflicts with another change I have waiting that gets rid of > aes_expandkey and that struct alltogether (since it was really just > abused to do a key size check, which was very wasteful since the > function actually generates all roundkeys we don't need at all ...)
Right, this is what I noticed there. With 480 of the 484 bytes gone, you are well below the warning limit even without the other change.
Arnd
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