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t=1787843685; bh=grSlt1xNPyLL4tvyZuMrw1Jdk2v1EacQiuP4ozz0DGE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=m++v6WxA/LOvDEGGypW0SjlIhjyDpeNH4FgOUZVSECUZyEPqIrL3aJzZUCk5HQBio q8miAEer7XWaO7Icx7tSUxgUeD/qmK8XunegrmDOkiO+ywOSXdWOe9lDyvRPSKmw6h 6Emxp+rcve0hP/PtpjlutVlCWVdF1hzvxtvnADYdP5Vp2ZXIjrchA2Quj0FNtNbI99 rTTEPLM90QSiYOHtBmQbl3scHCARoDWaVwGw3V+xuoxvebbSAuA0L1/oeMYEdbNC4f MbrdOwinoGbZx29qqL1DGdRWrzHcN/Ev1D4fzE1mPC46Pg/2kAacNyKlZhXjJa4b4W nfCknChKM+o9g== Message-ID: <4ead5df7-f000-4087-83e4-13aae036e0b7@kernel.org> Date: Thu, 27 Aug 2026 17:14:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/migrate_device: avoid out-of-bounds writes for compound folios To: Hui Su , akpm@linux-foundation.org, balbirs@nvidia.com Cc: ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260817120758.669807-3-sh_def@163.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: CAB8620003 X-Stat-Signature: tnjtqu711kuuktaanj6ma5zp8uezk6g7 X-Rspam-User: X-HE-Tag: 1787843686-834200 X-HE-Meta: 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 r9+Kk2sY Shtfil7kza3HbAQKHBrBFeWb4JwgVLhr9wEBJO4bWCzFhh2bKRW2i7HIlpWbik809X8ScEOxEdFlYJGjVg8NJS89RNsktHhZNwkIHDe4SmmTQ9a7lR2f+A5iaO2m+8Uui3zCBoje7DoV0crMqvpOqw19b0PAfE0Pec1xao2mcj8XqYdQFvYDDxeAhi5MfcelwL89A6RZzlzkyHPsvBeKVh4od4ZZWQUjU1ni8d99L1TlnhwTXJulg+LUBNZ0eiMfYOhbWsHqzuYwID2ACByP9gcU+Lr/qhfSL46V4O8PAxeTs2YkOsmK7dgJs3EmhwJ0DswYIXKeWBTALNDWOzOcOVbD7FUwGdzzvPVDiKZzoMwtezK6K1n/QCoNqG6ktmtDYa0G/j1NSc9WPNtPbOuGkIolzbCUADRHZ3uyNWMk4ZQCH1Snhxk9HuCqFI5zs+r2/xKidkghSm3U/2VQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/17/26 14:08, Hui Su wrote: > migrate_device_range() and migrate_device_pfns() clear the entries > following a compound folio so that the PFN arrays retain their > page-granular representation. > > If a compound folio extends beyond the end of the caller-provided range, > the loops clear all following folio entries without limiting them to the > number of slots remaining in the npages-sized array, causing an > out-of-bounds write. > > Do not proceed with a compound folio if its page-granular representation > does not fit entirely in the remaining PFN array. If this happens, drop > any reference and lock acquired for the folio, clear the remaining > entries, and stop collecting. > > Observed with a KASAN x86 QEMU kernel using the HMM > migrate_anon_huge_zero selftest. Closing /dev/hmm_dmirror0 after > migrating an anonymous huge page to device memory exercises: > > dmirror_fops_release() > -> dmirror_device_evict_chunk() > -> migrate_device_range() > > Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages") > Cc: stable@vger.kernel.org > Signed-off-by: Hui Su > --- > Changes in v2: > - Do not partially represent a compound folio when it does not fit in > the remaining PFN array. > - Drop any reference and lock acquired for that folio, clear the > remaining entries, and stop collecting, as suggested by Balbir Singh. > > v1: https://lore.kernel.org/lkml/20260817074350.442493-2-sh_def@163.com/ > > mm/migrate_device.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 908d2d4ec43a..69b8d0660bab 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -1400,6 +1400,15 @@ int migrate_device_range(unsigned long *src_pfns, unsigned long start, > > src_pfns[i] = migrate_device_pfn_lock(pfn); > nr = folio_nr_pages(folio); > + if (nr > npages - i) { > + if (src_pfns[i] & MIGRATE_PFN_MIGRATE) { > + folio_unlock(folio); > + folio_put(folio); > + } > + memset(&src_pfns[i], 0, > + (npages - i) * sizeof(*src_pfns)); > + break; > + } > if (nr > 1) { > src_pfns[i] |= MIGRATE_PFN_COMPOUND; > for (j = 1; j < nr; j++) > @@ -1434,6 +1443,15 @@ int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages) > > src_pfns[i] = migrate_device_pfn_lock(src_pfns[i]); > nr = folio_nr_pages(folio); > + if (nr > npages - i) { > + if (src_pfns[i] & MIGRATE_PFN_MIGRATE) { > + folio_unlock(folio); > + folio_put(folio); > + } > + memset(&src_pfns[i], 0, > + (npages - i) * sizeof(*src_pfns)); > + break; > + } > if (nr > 1) { > src_pfns[i] |= MIGRATE_PFN_COMPOUND; > for (j = 1; j < nr; j++) The code duplication here makes me angry. :) And using a memset on one branch but not on the other is weird. But is this the right fix or rather what https://lore.kernel.org/r/20260805231041.3791771-3-matthew.brost@intel.com tried? That fix would also need a cleanup but seems code-wise simpler. A cleanup could look like: diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 762c5cee8fecc..480bf59bc2425 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -1419,10 +1419,9 @@ int migrate_device_range(unsigned long *src_pfns, unsigned long start, for (pfn = start, i = 0; i < npages; pfn++, i++) { struct page *page = pfn_to_page(pfn); struct folio *folio = page_folio(page); - unsigned int nr = 1; + unsigned int nr = min(folio_nr_pages(folio), npages - i); src_pfns[i] = migrate_device_pfn_lock(pfn); - nr = folio_nr_pages(folio); if (nr > 1) { src_pfns[i] |= MIGRATE_PFN_COMPOUND; for (j = 1; j < nr; j++) @@ -1453,10 +1452,9 @@ int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages) for (i = 0; i < npages; i++) { struct page *page = pfn_to_page(src_pfns[i]); struct folio *folio = page_folio(page); - unsigned int nr = 1; + unsigned int nr = min(folio_nr_pages(folio), npages - i); src_pfns[i] = migrate_device_pfn_lock(src_pfns[i]); - nr = folio_nr_pages(folio); if (nr > 1) { src_pfns[i] |= MIGRATE_PFN_COMPOUND; for (j = 1; j < nr; j++) And as a further cleanup, we'd better de-duplicate that code and possibly use a memset for clearing, getting rid of j entirely. -- Cheers, David