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Message-ID: <202209221446.5E90AEED@keescook> Date: Thu, 22 Sep 2022 14:49:08 -0700 From: Kees Cook <keescook@...omium.org> To: Vlastimil Babka <vbabka@...e.cz> Cc: Christian König <christian.koenig@....com>, Pekka Enberg <penberg@...nel.org>, Feng Tang <feng.tang@...el.com>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Alex Elder <elder@...nel.org>, Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>, Sumit Semwal <sumit.semwal@...aro.org>, Jesse Brandeburg <jesse.brandeburg@...el.com>, Daniel Micay <danielmicay@...il.com>, Yonghong Song <yhs@...com>, Marco Elver <elver@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, netdev@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, linux-fsdevel@...r.kernel.org, intel-wired-lan@...ts.osuosl.org, dev@...nvswitch.org, x86@...nel.org, linux-wireless@...r.kernel.org, llvm@...ts.linux.dev, linux-hardening@...r.kernel.org, Hyeonggon Yoo <42.hyeyoo@...il.com> Subject: Re: [PATCH 00/12] slab: Introduce kmalloc_size_roundup() On Thu, Sep 22, 2022 at 11:05:47PM +0200, Vlastimil Babka wrote: > On 9/22/22 17:55, Kees Cook wrote: > > On Thu, Sep 22, 2022 at 09:10:56AM +0200, Christian König wrote: > > [...] > > > So when this patch set is about to clean up this use case it should probably > > > also take care to remove ksize() or at least limit it so that it won't be > > > used for this use case in the future. > > > > Yeah, my goal would be to eliminate ksize(), and it seems possible if > > other cases are satisfied with tracking their allocation sizes directly. > > I think we could leave ksize() to determine the size without a need for > external tracking, but from now on forbid callers from using that hint to > overflow the allocation size they actually requested? Once we remove the > kasan/kfence hooks in ksize() that make the current kinds of usage possible, > we should be able to catch any offenders of the new semantics that would appear? That's correct. I spent the morning working my way through the rest of the ksize() users I didn't clean up yesterday, and in several places I just swapped in __ksize(). But that wouldn't even be needed if we just removed the kasan unpoisoning from ksize(), etc. I am tempted to leave it __ksize(), though, just to reinforce that it's not supposed to be used "normally". What do you think? -- Kees Cook
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