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Received: from loth.rohan.me.apana.org.au ([192.168.167.2]) by formenos.hmeau.com with smtp (Exim 4.96 #2 (Debian)) id 1wN2Ny-00DhFl-1i; Wed, 13 May 2026 13:43:59 +0800 Received: by loth.rohan.me.apana.org.au (sSMTP sendmail emulation); Wed, 13 May 2026 13:43:58 +0800 Date: Wed, 13 May 2026 13:43:58 +0800 From: Herbert Xu To: Sergey Senozhatsky Cc: Andrew Morton , Yosry Ahmed , Kartik Nair , minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+8f77ff6144a73f0cf71b@syzkaller.appspotmail.com, Nhat Pham Subject: Re: [PATCH] zsmalloc: zero-initialize zspage memory to prevent KMSAN uninit reads Message-ID: References: <20260511213658.25273-1-contact.kartikn@gmail.com> <20260512144733.9132c83e392a109743e92f71@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B95F4120009 X-Rspam-User: X-Stat-Signature: 5ga5qxg3y5xoy989j7gob3d6zq93ny3e X-HE-Tag: 1778651048-908357 X-HE-Meta: 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 SRKFAz2L NlsaSoAcZf498eN3OgSWuivjuucr35yDS0dEVgmr3aj6RFc+nT/SlsPePBuwdyKLor4HG7xqk5z0qj/EsORB7DTxubBQIyy9AxPgjIv7wPRqn3euYIT8+w10RM7VSbbua2qPe+xN2tJR4aPhkaHepiPGf2tilLHavw34w3+gm17bSiDfxeKpUkK2Av5rB6f9YwPSisnaXV1Rv+08VtJHg4n9T6l1v69iMdKEcmg360XwKCN1iGU/J+KkXmDsw4sZ0KIJC5OjfprvfWJhMBrW+ospRZWl9gSZcI3Vy3ib9xYWZnPq/F1WNimFY0c7V0Ywc1UmLGOnTQx/t5cpI6BecUgjO0yM5O2/5IIwBlughL+AJhrsf59OEjbirq6dlrEXhRLkN Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 13, 2026 at 11:47:41AM +0900, Sergey Senozhatsky wrote: > Adding Yosry and Herbert, > > On (26/05/12 14:47), Andrew Morton wrote: > > > Pages allocated via alloc_zpdesc() use alloc_pages_node() without > > > __GFP_ZERO, leaving physical memory uninitialized. When a compressed > > > object spans two physical pages in a zspage, zs_obj_read_sg_begin() > > > sets up a scatterlist pointing directly at the raw second page. If the > > > second page was freshly allocated and never written beyond the object > > > boundary, KMSAN detects reads of uninitialized memory downstream in > > > the decompressor (e.g. sw842_decompress reading the CRC trailer). > > I don't get this. How can sw842_decompress() read more bytes than > it's told to decompress. We first compress and store the object, > before we load and decompress, reading past the known compressed > object size (which we pass to decompress function) should not happen. > Yosry, Herbert, any ideas? It sounds like a bug in 842. I'll look into it. Thanks for pointer. -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt