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List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] btrfs: Fix BTRFS arm64 tagged KASAN false-positive To: Daniel J Blueman , Qu Wenruo , David Sterba , Chris Mason , dsterba@suse.cz Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com References: <20260319053413.14771-1-daniel@quora.org> <4d6f78d3-f274-43e1-adc8-c4fff4f85e24@suse.com> <20260320220137.GI5735@twin.jikos.cz> <33164dbf-ab81-4611-ba1a-e6e187bfaf51@suse.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB 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/I+Xk1WvCxDg84Xh1WHtkbS65AWPxordAES5WH/NnUq0nLLGBORGuJQuAxuk1aZYqTkJapgFo y5Wu/yGOLNGGVmY9N9fVR56RpExZM7Sn5sV4BRFIg5UKgrMwygsxXGVtBK8HfsvfhCuxm1Bb5 1ceEVtZJVCmFppGaau//4jD4QHCw4ziYDtAjuhituDAjNE4rYAmbOGp3JbeoDnrqlVFlgkRaf Ei0vFVdOxkedBE95GMWjDjOpdjTdyKKjFNfmvpr+oLD+IWmvhCkO4rgan1LA8VUT8id++3N+p /YP8ictvrdnqDIDWkrYcdPabe96FMVlMhAo4BvkE1B9NBD+ThGYnQYEmWgWYnQ7Bh200g96oN D6AYjq3Xeug25U3OBuj67p1+g1+fP/rm34CbzMzfbsibVVHKj7X9vT2RxDzPgbkq3TS4xuC3S cd/H75goG2SUeknZClArYhZJSXiMgEAAdi1havzFO9JcGzeRhZYuax/CoHjWdmI= =E5=9C=A8 2026/3/21 13:09, Daniel J Blueman =E5=86=99=E9=81=93: > On Sat, 21 Mar 2026 at 06:27, Qu Wenruo wrote: >> =E5=9C=A8 2026/3/21 08:31, David Sterba =E5=86=99=E9=81=93: >>> On Thu, Mar 19, 2026 at 07:26:34PM +1030, Qu Wenruo wrote: [...] >> >> There is the interface, page_kasan_tag_set()/page_kasan_tag_reset(), an= d >> is already utilized inside MM. >> >> And the deeper problem is, if this is a false alert, shouldn't we fix >> the sanitizer? >> >> Especially in this case I didn't see any problem accessing properly >> allocated and physically adjacent pages. >=20 > I agree with this, however BTRFS doesn't have multi-page folios, thus > these pages are from different allocations; from extent_io.c: >=20 > /* For now, we should only have single-page folios for btree inode. */ > ASSERT(folio_nr_pages(existing_folio) =3D=3D 1); >=20 > The goal of the differing KASAN tags per allocation is to catch UAF > and other lifecycle issues. If preferred, I can test and submit a > patch to set the same KASAN tag in alloc_eb_folio_array()? This would > be removed when multi-page folio support is added and is along the > lines of: >=20 > for (int i =3D 1; i < num_pages; i++) > page_kasan_tag_set(page_array[i], page_kasan_tag(page_array[0])); That's exactly what I expect. >=20 > It will be less minimal as won't implicitly be compiled out as per my > previous patch. To be honest, I think the above change is the minimal fix, as it doesn't= =20 inject kasan code into the main loop of folio allocation. And it will be compiled out, as page_kasan_tag_set() is no-op if neither= =20 software nor hardware tag is selected, and I believe the compiler is=20 definitely clever enough to remove a loop with no-op in it. Thanks, Qu >=20 > Thanks, > Dan