On 18 July 2018 at 23:50, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > On 18 July 2018 at 05:59, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> On Sun, Jul 15, 2018 at 6:28 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: >>> >>> After my ahash to shash conversions, only ccm is left as an ahash >>> user, since it actually uses sg. But with the hard-coded value reduced >>> to 376, this doesn't trip the frame warnings any more. :) >>> >>> I'll send an updated series soon. >> >> Maybe we should get rid of that one as well then and remove >> AHASH_REQUEST_ON_STACK()? >> >> I see that Ard (now on Cc) added this usage only recently. Looking >> at the code some more, I also find that the descsize is probably >> much smaller than 376 for all possible cases of "cbcmac(*)", >> either alg->cra_blocksize plus a few bytes or sizeof(mac_desc_ctx) >> (i.e. 20) for arch/arm64/crypto/aes-glue.c. >> >> Walking the sglist here means open-coding a shash_ahash_update() >> implementation in crypto_ccm_auth(), that that doesn't seem to >> add much complexity over what it already has to do to chain >> the sglist today. >> > > It would be better to add a variably sized ahash request member to > struct crypto_ccm_req_priv_ctx, the only problem is that the last > member of that struct (skreq) is variably sized already, so it would > involve having a struct ahash_request pointer pointing into the same > struct, after the skreq member. Actually, I think the below should already do the trick: ahreq and skreq are not used at the same time, so we can stick them in a union, and take the max() of the reqsize to ensure there's enough empty space after it. --------8<---------- diff --git a/crypto/ccm.c b/crypto/ccm.c index 0a083342ec8c..b242fd0d3262 100644 --- a/crypto/ccm.c +++ b/crypto/ccm.c @@ -50,7 +50,10 @@ struct crypto_ccm_req_priv_ctx { u32 flags; struct scatterlist src[3]; struct scatterlist dst[3]; - struct skcipher_request skreq; + union { + struct ahash_request ahreq; + struct skcipher_request skreq; + }; }; struct cbcmac_tfm_ctx { @@ -181,7 +184,7 @@ struct crypto_ccm_req_priv_ctx *pctx = crypto_ccm_reqctx(req); struct crypto_aead *aead = crypto_aead_reqtfm(req); struct crypto_ccm_ctx *ctx = crypto_aead_ctx(aead); - AHASH_REQUEST_ON_STACK(ahreq, ctx->mac); + struct ahash_request *ahreq = &pctx->ahreq; unsigned int assoclen = req->assoclen; struct scatterlist sg[3]; u8 *odata = pctx->odata; @@ -427,7 +430,7 @@ crypto_aead_set_reqsize( tfm, align + sizeof(struct crypto_ccm_req_priv_ctx) + - crypto_skcipher_reqsize(ctr)); + max(crypto_ahash_reqsize(mac), crypto_skcipher_reqsize(ctr))); return 0;