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Fri, 25 Sep 2026 00:42:43 -0700 (PDT) Received: from localhost ([2c0f:3d00:6be:8900:ce5e:9212:ea4b:f30]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4887a355d96sm5487752f8f.17.2026.09.25.00.42.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Sep 2026 00:42:42 -0700 (PDT) Date: Fri, 25 Sep 2026 10:42:38 +0300 From: Dan Carpenter To: Arnd Bergmann Cc: oe-kbuild@lists.linux.dev, kernel test robot , oe-kbuild-all@lists.linux.dev, linux-kernel@vger.kernel.org, Juergen Gross , xen-devel@lists.xenproject.org, Stefano Stabellini , Oleksandr Tyshchenko Subject: Re: drivers/xen/gntdev.c:817 gntdev_get_page() warn: mask and shift to zero: expr='(addr & ~(~((1 << 12) - 1))) >> 12' Message-ID: References: <202609241805.VsLzGPLn-lkp@intel.com> <94cbe491-1b32-47ec-a9b5-bed69bc4d52c@app.fastmail.com> Precedence: bulk X-Mailing-List: oe-kbuild@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <94cbe491-1b32-47ec-a9b5-bed69bc4d52c@app.fastmail.com> On Fri, Sep 25, 2026 at 08:43:54AM +0200, Arnd Bergmann wrote: > On Thu, Sep 24, 2026, at 21:39, Dan Carpenter wrote: > > > 489 return -EFAULT; > > 490 break; > > 491 case 2: > > 492 if (copy_from_user(&m, udata, sizeof(struct > > privcmd_mmapbatch_v2))) > > 493 return -EFAULT; > > 494 /* Returns per-frame error code in m.err. */ > > 495 if (!access_ok(m.err, m.num * (sizeof(*m.err)))) > > ^^^^^^^^^^^^^^^^^^^^^^^ > > These integer overflow bugs are from 2012, but I guess your patch > > exposed > > the arm32 build to the zero day bot. The bugs only affect 32bit > > systems. > > Right, the randconfig came up with an ARMv6 Xen build, which was not > possible before my patch. I'm sure this was reported for other configs > before and just showed up as introduced by my patch here. > > This is clearly a bug but it does look harmless to me, as it only > results in the userspace corrupting itself when passing invalid > data. In ancient times, these access_ok() overflows were a much bigger deal. Easy to solve with a size_mul(m.num, sizeof(*m.err)). regards, dan carpenter