Messages in this thread | | | Date | Fri, 15 Apr 2022 13:18:53 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN |
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On Fri, Apr 15, 2022 at 10:05:21AM +0200, Ard Biesheuvel wrote: > On Fri, 15 Apr 2022 at 09:52, Herbert Xu <herbert@gondor.apana.org.au> wrote: > > On Fri, Apr 15, 2022 at 09:49:12AM +0200, Ard Biesheuvel wrote: > > > I'm not sure I understand what would go wrong if that assumption no > > > longer holds. > > > > It's very simple, we don't do anything to the pointer returned > > by kmalloc before returning it as a tfm or other object with > > an alignment of CRYPTO_MINALIGN. IOW if kmalloc starts returning > > pointers that are not aligned to CRYPTO_MINALIGN then we'd be > > lying to the compiler. > > I guess that should be fixable. GIven that this is about padding > rather than alignment, we could do something like > > struct crypto_request { > union { > struct { > ... fields ... > }; > u8 __padding[ARCH_DMA_MINALIGN]; > }; > void __ctx[] __align(CRYPTO_MINALIGN); > }; > > And then hopefully, we can get rid of the padding once we fix drivers > doing non-cache coherent inbound DMA into those structures.
But if we keep CRYPTO_MINALIGN as 128, don't we get the padding automatically?
struct crypto_request { ... void *__ctx[] CRYPTO_MINALIGN_ATTR; };
__alignof__(struct crypto_request) == 128; sizeof(struct crypto_request) == N * 128
The same alignment and size is true for a structure like:
struct crypto_alg { ... } CRYPTO_MINALIGN_ATTR;
Any kmalloc() of sizeof(the above structures) will return a pointer aligned to 128, irrespective of what ARCH_KMALLOC_MINALIGN is.
The problem is if you have a structure without any alignment attribute (just ABI default), making its sizeof() smaller than ARCH_DMA_MINALIGN. In this case kmalloc() could return a pointer aligned to something smaller. Is this the case in the crypto code today? I can see it uses the right alignment annotations already, no need for kmalloc() hacks.
-- Catalin
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