On Wed, Sep 26, 2018 at 10:44 AM Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > > On Tue, 25 Sep 2018 at 18:12, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > On Tue, Aug 7, 2018 at 11:18 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > > > > In the quest to remove all stack VLA usage from the kernel[1], this uses > > > the new upper bound for the stack buffer. Also adds a sanity check. > > > > > > [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx > > > > > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > > > After rebasing to linux-next, I now get a warning about this file: > > > > drivers/crypto/qat/qat_common/qat_algs.c: In function 'qat_alg_do_precomputes': > > drivers/crypto/qat/qat_common/qat_algs.c:257:1: error: the frame size > > of 1112 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] > > > > I assume it was already possible to get into that state with the VLA, > > but it seems bad enough that I think we need to do something > > about it. > > > > The large stack variables add up to 1084 bytes, which fully explains > > how we got here: > > > > SHASH_DESC_ON_STACK(shash, ctx->hash_tfm); /* 360 */ > > struct sha1_state sha1; /* 92 */ > > struct sha256_state sha256; /* 104 */ > > struct sha512_state sha512; /* 208 */ > > char ipad[MAX_ALGAPI_BLOCKSIZE]; /* 160 */ > > char opad[MAX_ALGAPI_BLOCKSIZE]; /* 160 */ > > > > The question is what we can do about it. One simple step I've tried > > is to move the sha1/sha256/sha512 into a union, which saves around > > 200 bytes and should bring us (slightly) below the warning > > limit, but I suspect we can do better than that. Any ideas? > > > > All the processing takes place in the context of a setkey() operation, > which means only one such operation should be in flight per tfm at any > given time. So we could move all these pieces into the tfm context > struct instead. Something like the below [untested] (whitespace > mangling courtesy of Gmail) Ah, right, this is what I was hoping for. I assume we already guarantee that this context is never put on the stack somewhere else, right? Arnd
