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b=FTMSNTZX8kORLzAsEEIX5Ti4RgZXoKJwhdVWVtI24hgp01OaWheb1weeKKyJB23KW Xhd3E/Fc4yQ0NGYhb7tJLVAKCA3URPXG7P0GRbu61HCzOtTcFTDpzXS7X6TyRQFd3y TkdoRkHvUUMIv2z6tgsqktbcAXoqCmXQprReq1EQLidWND6DDcuktfmKGXxu26drCl wTv1+CoLP6os8Nz4YJYlZlj48ok4+TXIgtIkObA0JuvMI29TtKGWdqkHmR9EdIO5WC ClmhduuEkBYFznTm3FstgsRQVbs3AtVUGyI8S7bm//qcehRJxMumicZbIKpfCH+QqU oDXvRl5ppTFdQ== Date: Thu, 24 Apr 2025 11:42:39 -0700 From: Kees Cook To: Danilo Krummrich Cc: Andrew Morton , Erhard Furtner , Michal Hocko , Vlastimil Babka , Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] mm: vmalloc: Support more granular vrealloc() sizing Message-ID: <202504241136.8B4E729@keescook> References: <20250424023119.work.333-kees@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: kxd1mka73bbqyyfaknkfqtob6ue4gjni X-Rspamd-Queue-Id: 41CF11A000D X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1745520163-551001 X-HE-Meta: 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 mbhUyRCV LO6QV657OyeX+2cH/dYjLaA2un1xBM9X8iMMp7J4vAPv3moWvj0kaI7Y2fCCdMTWmT2/yMlospokdxP88gdzPT9KPt0YKBj+//qkPlXGhFQyY5euqiiO8URUKfIR+PKM+WlusMw6A1ldaDwYf18xGTfq4NVdbx8F51u644LM85YHASPkCy1RLEml3Wx3Tgy3PcwIiqK0NsHIAFRdv2Jp/F49TTRrpMFkkA2ZDuntX+rgGXgYTPxoexmf/C0DkTitXLMwfAEKjLpTPpy/nRthA6ZvgSkzWchV1Y7cIsAi4UHLXogrA11sjuH6WKoPTOaNx9qemiT5pZoJTZjE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 24, 2025 at 11:11:47AM +0200, Danilo Krummrich wrote: > On Wed, Apr 23, 2025 at 07:31:23PM -0700, Kees Cook wrote: > > Introduce struct vm_struct::requested_size so that the requested > > (re)allocation size is retained separately from the allocated area > > size. This means that KASAN will correctly poison the correct spans > > of requested bytes. This also means we can support growing the usable > > portion of an allocation that can already be supported by the existing > > area's existing allocation. > > > > Reported-by: Erhard Furtner > > Closes: https://lore.kernel.org/all/20250408192503.6149a816@outsider.home/ > > Fixes: 3ddc2fefe6f3 ("mm: vmalloc: implement vrealloc()") > > Signed-off-by: Kees Cook > > Good catch! > > One question below, otherwise > > Reviewed-by: Danilo Krummrich > > > @@ -4088,14 +4093,27 @@ void *vrealloc_noprof(const void *p, size_t size, gfp_t flags) > > * would be a good heuristic for when to shrink the vm_area? > > */ > > if (size <= old_size) { > > - /* Zero out spare memory. */ > > - if (want_init_on_alloc(flags)) > > + /* Zero out "freed" memory. */ > > + if (want_init_on_free()) > > memset((void *)p + size, 0, old_size - size); > > + vm->requested_size = size; > > kasan_poison_vmalloc(p + size, old_size - size); > > kasan_unpoison_vmalloc(p, size, KASAN_VMALLOC_PROT_NORMAL); > > return (void *)p; > > } > > > > + /* > > + * We already have the bytes available in the allocation; use them. > > + */ > > + if (size <= alloced_size) { > > + kasan_unpoison_vmalloc(p, size, KASAN_VMALLOC_PROT_NORMAL); > > + /* Zero out "alloced" memory. */ > > + if (want_init_on_alloc(flags)) > > + memset((void *)p + old_size, 0, size - old_size); > > + vm->requested_size = size; > > + kasan_poison_vmalloc(p + size, alloced_size - size); > > Do we need this? We know that old_size < size <= alloced_size. And since > previously [p + old_size, p + alloced_size) must have been poisoned, > [p + size, p + alloced_size) must be poisoned already? > > Maybe there was a reason, since in the above (size <= old_size) case > kasan_unpoison_vmalloc() seems unnecessary too. Honestly I was just copying the logic from the prior case. But yeah, it should be possible (in both cases) to just apply the changed span. For the "size <= old_size" case, it would just be: kasan_poison_vmalloc(p + size, old_size - size); (i.e. the kasan_unpoison_vmalloc() call isn't needed at all, as you say.) And in the "size <= alloced_size" case, it would just be: kasan_unpoison_vmalloc(p + old_size, size - old_size, KASAN_VMALLOC_PROT_NORMAL); and no kasan_poison_vmalloc() should be needed. Do the KASAN folks on CC have any opinion on best practices here? Thanks for looking it over! -Kees -- Kees Cook