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b=Om6KcrXu8DE2JhUZs0+F2J+y4aA2hbY89smr4crrjx5cRej3tpnwOxli02mGOXb5b 0HZvTa5Zfc83wD+u2NAxu5b7wvyTPBmHCZiD+dySxaGGzRg0SxQpDz5fDdp9gdzJlb Obs5tI+hxPgFgGOf2mx7oJ3SOuqr6d+c6LP4BxUU= Date: Thu, 19 Mar 2026 19:37:35 -0700 From: Andrew Morton To: Marco Elver Cc: Alexander Graf , Mike Rapoport , Pasha Tatashin , Pratyush Yadav , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com Subject: Re: [PATCH v2] kho: use checked arithmetic in deserialize_bitmap() Message-Id: <20260319193735.2ea34594b36d37e7850a8c37@linux-foundation.org> In-Reply-To: <20260319210528.1694513-2-elver@google.com> References: <20260319210528.1694513-2-elver@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AAEDE120004 X-Stat-Signature: ss3awzbpngzitjx6194ckxtuab8355n6 X-Rspam-User: X-HE-Tag: 1773974257-230799 X-HE-Meta: U2FsdGVkX1+6JIoM4ysTe2UxMzZbRLm2kwkfFD1JKMntANOCqO9h2xh0tHmQVxZRh7tVWAKp/aEjxKvqFJWbC8r9Bx5gI5GJWKyUTKax9pO/DhGdORJwQ2xk3g/yYQXrPJBFOrnOqGcvXTk5tYUfi2PZSaxKIOsQubeXIxxzODyLdO/NZI7XEXB3r6+I9iMwIE1WLnng0F/nXXhpV6kzu78FFG7hmsk5nkMshJZ5Qt6tJXyJFSq1FB2wWv5GRSMx5/H1wbD5REYtaOMBoRiooJlU7hQ3z+dD9ZUjirLE64xX/9M9ZtIki5bxmYnuwfLUePaenAk/jz4jPrAfsM5xE0M1V5PL9EDO0nO0KwGnfqtQA3xKLGr4NYOTkzB+hGO8QSFwRt7horqOERabAh5fQaL2p07Pi5qli+0rKD0BzD4DzZAScvxwQ8EGqIqzIWhxAt72AoP1D00jwAhXgnkNYaCSrli/IkrFz8ktBKUkY05kp1NCWiToLDOehpn/955KZwMLIcIQVggvZ24MTG45FA9QxMK7Itq8Zo7cVjQtILPnxA4IUF1dglHxu0u3aSqUyr3pbPGB5Cp5k9gflFOTBDdvKD+Pkq4akMtHPf1hf1UzsK5o2yHm84dAShrTffW6Llxo2kWoDqNrpTX3soQ/56vUS+37vW12uhwnxuJf1ZDp6bCRyX2y+Axzbr5bsGZbr5dD/DdSowkuqlXbsmTKGbtEb/OmrX1LsnGuViP9Aay6tO3HPPq+wbYq3/dkmg+pOXxQ9qe7tQfOJDBy30od0+dvfCdlFiPIOwuC6xrM7gTEMziH+FZz5ZXWoFfDq18TyNP3n/tJK0d2TBPbyb4K9FHKdmHXdbc74TOPejG+nFo1ubSoQqClDgcDWdKCRvjq88O9CsPUs6v1Awd62eMSQjJr6HFpQDoJmZsCEH+x6tNRTlbeLC88en3N+1UmxLgj+EG1MipgvTeEkyNPMqs PPYAJiYu PUobImHf2ei9NeRYW3GSo1wh6vLGxylMx4nDrL5IhPtSIQN31lFOPuDkvzWVnHbCyX+XuhSvn2NAALRNRLedzK0Z0EJfu0QokvP/QqkpgDZikGna+QCrf3raOXXgk8FItLtunfvu93oq7D1N8hW+/q3thECxlT3sY1fnek+rwcFRKP7p5IBPTJMT9lluaD4My5SOtyBJ9Y1fo+Bqu+5g6rxtGVwTTphoGS6UNemXiHPPBDwIQAGSnwjx/ZTU+UZgMpmyd0OcuXiyv92N4UmtdrQUkG3zXUMoXUeHc2ni5a7pt/UL8rLTBwzD3timOoGKZG1hdoSQjUO9R15Zxc6BIm2wi2MFsEDqhmZUTlOeghFyBy1GhXaquyNEsCi1S41vroC7f Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 19 Mar 2026 22:03:53 +0100 Marco Elver wrote: > The function deserialize_bitmap() calculates the reservation size using: > > int sz = 1 << (order + PAGE_SHIFT); > > If a corrupted KHO image provides an order >= 20 (on systems with 4KB > pages), the shift amount becomes >= 32, which overflows the 32-bit > integer. This results in a zero-size memory reservation. > > Furthermore, the physical address calculation: > > phys_addr_t phys = elm->phys_start + (bit << (order + PAGE_SHIFT)); > > can also overflow and wrap around if the order is large. This allows a > corrupt KHO image to cause out-of-bounds updates to page->private of > arbitrary physical pages during early boot. > > Fix this by changing 'sz' to 'unsigned long' and using checked add and > shift to safely calculate the shift amount, size, and physical address, > skipping malformed chunks. This allows preserving memory with an order > larger than MAX_PAGE_ORDER. AI review asked questions: https://sashiko.dev/#/patchset/20260319210528.1694513-2-elver%40google.com