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a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789150588; bh=pXkt8h/Jok9K7Q3feytS1db7RvHnBcGlzZ45+6I/na4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=X99XCYO7J5latPOdtROUfGkWNMIZoKp9nscpYoI4bUZPyx9DTxg99Cd6v1kiNCHYi z/B9/nTxxuFhaNEnIQERpDHVoU9VBn3zqR04M3D61ga4pBpCpNi48pY4OrPl0ZPDq1 luBs+w7JZwyu03/ggVvbbW0knu5oiouEX1O6Ij7WjcboyN9tekmeaT5jufsiH004XK 2k+ak0Fxj1KN70ahhHBLh+if7rlUrRWJNdN0bUfqNl4yxZwPVi25ClsfxxSAreGdRK AGypfPnMXrYpmlOZEk4fruLO4myYSm9gmCS9eCTYMSH4GUWs+XGV2s03qVJYgRnF5V QrqZ1pi2UTKEA== Message-ID: <376e2b66-c0f7-4064-8e38-997fad4df5b3@kernel.org> Date: Fri, 11 Sep 2026 20:16:21 +0200 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> <366c39ee-d452-4a1c-af0d-2badd4d8210f@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 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 3302614000D X-Stat-Signature: 38hncnrts4jgyhze6ap4gm8fjshoezdm X-HE-Tag: 1789150589-245877 X-HE-Meta: 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 ms2XzK7B Atp94vdCP1ujLpU2l1861APQiTrm4Eok3DnUOV+lJOy+mXvNH9xjDUAJcOVjksUwxzDZElXDJ6CT0TDEvLiddZOf1Xp9iDcsNMEuiVPiDIaoQ9NiTAX7BCGrusGKL8K5ft8hiRvciWk1zZ3hOdSPr/eY81i1+Pz2uWw5RXHArgAZXBU5lrMlfEqeFktMtlAVrdFjfThqt4pEGbBjHUVPy17OtXP8fnPFPPstZdPOv5Uqsnr3n/mOgo1iLrmRS+h6ZYGVJA6sam4pcRkZeoaMn0rjWF/gdE5DX/i6jcSwWiA3mpYBuIgAzH79vHhKFVbqC+B12ePDiOS4Fcr/kBx5th11UV65+n6s6OgBk6vMt7L3/Hq+Gt+Eb3sd6ykMFFvyYoYmPFt0AODnIo+k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/11/26 14:13, Sarthak Sharma wrote: > Hi David! > > On 9/7/26 8:20 PM, David Hildenbrand (Arm) wrote: >> 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? > > Yes, it is possible in 2 cases: > > 1. We calculate end as gup->addr + gup->size. So, if gup->size is not > page aligned, then at some point, we can have (end - addr) < PAGE_SIZE > and (end != addr). Then (end - addr) / PAGESIZE will be 0. Right now all > callers seem to provide a page aligned gup->size, but any userspace > program which can open /sys/kernel/debug/gup_test can provide a non page > aligned gup->size. Note that this is a pure testing interface. So we don't care about weird user space doing stupid things. Rather reject unaligned gup->size early in __gup_test_ioctl(). > > 2. If the userspace supplies nr_pages_per_call = 0 (we never validate > nr_pages_per_call so it is possible). > Same here, user space won't do that. If you want to be sure, rather reject exactly that early in __gup_test_ioctl(). Something like diff --git a/mm/gup_test.c b/mm/gup_test.c index 185ba3bb8ed10..9e3e1df8dd526 100644 --- a/mm/gup_test.c +++ b/mm/gup_test.c @@ -116,7 +116,8 @@ static int __gup_test_ioctl(unsigned int cmd, bool needs_mmap_lock = cmd != GUP_FAST_BENCHMARK && cmd != PIN_FAST_BENCHMARK; - if (gup->addr > ULONG_MAX || gup->size > ULONG_MAX) + if (gup->addr > ULONG_MAX || gup->size > ULONG_MAX || !gup->size || + !PAGE_ALIGNED(gup->size)) return -EINVAL; if (check_add_overflow((unsigned long)gup->addr, (unsigned long)gup->size, &end)) > Sorry for the delay, your email didn't reach my inbox due to some reason :) No worries. -- Cheers, David