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 TocK30r4 IGdxA3PHuPJU8FlEeeBAtenbdbHRmSNfBMitp4pZgnvDNE6bo0eyQnBm/M2GyJfaWnCU9sVTQBBn6Ir+bMN/vMwt4yFcICz3jq34TRwfs69+0gLwS2RdWJmvfMyxgJHcLAsON15y1TFIJVPokEySAbwiyhDpHfM2Gs99/GMBZSaIglw31UDql6U7g6dfHKTG59VV6 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 Fri, Apr 04, 2025 at 11:30:49AM +0200, Vlastimil Babka wrote: > Hi, > > due to some off-list inquiry I have realized that since 946fa0dbf2d8 > ("mm/slub: extend redzone check to extra allocated kmalloc space than > requested") > we might be reporting false positives due to dma writing into the redzone. > > It wasn't confirmed (yet) during the conversation but AFAICS it can be > happening. We have this ARCH_DMA_MINALIGN and kmalloc() will guarantee it, > but the redzone check doesn't take it into account. Sounds valid to me. > So if it's 8 bytes, I think it's valid to do e.g. kmalloc(60), get a 64 byte > object, do a dma operation and it can write into the last 4 bytes. > But the redzone check will then report a buffer overflow. > > Do you agree? If yes we should probably align the redzone with > ARCH_DMA_MINALIGN even if it means not reporting some non-dma buffer > overflows anymore. Hmm then to fix it, we need to only do the extended redzone check starting from + align(req_size, ARCH_DMA_MINALIGN), instead of + req_size? For instance, if req_size is 33 bytes and it's aligned to 40 bytes, a 64-byte object will be allocated. Then the extended redzone check should only cover the remaining 14 bytes. -- Cheers, Harry (formerly known as Hyeonggon)