From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D4354534A5 for ; Mon, 7 Sep 2026 14:50:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788792616; cv=none; b=S4Y2NdjtG31bS9tyan0gKK94LbBZHWgxAqgbouIJNkOj5ihCd4k1BDMR9ifbPZ88zGXhThn2mAa60NL+Bf+VelKJlMdA9+/dX2uoFWgHQabWsDrGMxlgqXwJUDEkT/Y7Q6S+2ylsAPXaS55GZaNiVIYLz+O8CSShAvcU3Cc7C3k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788792616; c=relaxed/simple; bh=qg0EgdC1JYpqPJvrqMKjHwBv5u7+1NBON6XbAclWwsQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AIvXh6vVqj5qAG+mz6GLHyjXM0QWXIWFbzlcOcuJuedWLcZMuPkhI12XQEf5kvvBuAJhLn/WttV2B3f+iwo1HAVAfU8PlWTcyliU7DjspFw2iWyN/xNsgpL+UNC2DNmJza3dmO0PZlAVMSain2JJGaOy0hhxYnohHp8In4yznFk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oBBZei8f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oBBZei8f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4F42B1F00A3A; Mon, 7 Sep 2026 14:50:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788792608; bh=0mIRzAim8Xm04hf6n5NB+NxEk+eE5bXm5v665dJOtpg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=oBBZei8fiHVJieUd7Lx21QpFtUu+KnLLeLIBYbntsp5gB1HSyOzJ2aCxPwQTrnzsR ZAV5ezYF7K8Svj2yPyUBGosD9SRvb0Pk+1Bi9o1dFVWx2Tv/7jSjX6oi0HUYKze38r ZkDapIB5ST8+zWkvJyYsQ1rbKV3Oh2LQJvhhfw4H+6HsGG5zQC0+FPDYOJBXL2FSk1 dj6BTOsA7RqNsT0El6XVcv6nydL4/FdBaq9zC3Oc0FOe5VSIZEu2+qjJDRuhMI+fyC QMEJVhJUA/B5pP68gI7p3UQ4lFuzH1BYO9AcCR58lwusE8FgQzCK4yHGJmzAQfoGal M+e2/iEYEUDDw== Message-ID: Date: Mon, 7 Sep 2026 16:50:04 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm/gup_test: safely calculate GUP batch size To: Sarthak Sharma , Andrew Morton Cc: Jason Gunthorpe , John Hubbard , Peter Xu , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260903115033.162218-1-sarthak.sharma@arm.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 On 9/3/26 13:50, Sarthak Sharma wrote: > __gup_test_ioctl() calculates the end of a GUP batch using: > > next = addr + nr * PAGE_SIZE; > > If nr is too large, it can cause next to overflow and wrap around. > If it wraps, the next > end check is bypassed and a large value > of nr is passed to the GUP call, even though the pages array was > allocated according to gup->size. This can lead to out of bounds writes. > > Also, when fewer than PAGE_SIZE bytes remain, the calculated batch > contains zero pages. The code still calls GUP functions with pages + i, > which can point past the allocated array. > > Calculate nr by taking the minimum of the number of pages per call and > the pages remaining in the address range. Stop processing when no > pages remain and calculate the end of the batch using this bounded > value of nr. > > Fixes: 64c349f4ae78 ("mm: add infrastructure for get_user_pages_fast() benchmarking") > Signed-off-by: Sarthak Sharma > --- > Sashiko reported the issue fixed by this patch while reviewing the patch > "mm/gup_test: report actual pinned bytes". That patch has been applied to > mm-new. Since the two fixes are independent, this revision contains > only the GUP batch size fix. > > Changes in v4: > - Simplify batch clamping logic as suggested by Kiryl > - Don't call GUP functions for an empty batch > - Drop the pinned byte reporting patch since it has been applied to mm-new > > v3: https://lore.kernel.org/all/20260901083452.115365-1-sarthak.sharma@arm.com/ > > mm/gup_test.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/gup_test.c b/mm/gup_test.c > index 185ba3bb8ed1..1b64e932c4c5 100644 > --- a/mm/gup_test.c > +++ b/mm/gup_test.c > @@ -139,11 +139,12 @@ static int __gup_test_ioctl(unsigned int cmd, > if (nr != gup->nr_pages_per_call) > break; > > + nr = min_t(unsigned long, gup->nr_pages_per_call, > + (end - addr) / PAGE_SIZE); > + if (!nr) > + break; Can !nr actually happen? -- Cheers, David