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 1A2772EC083; Thu, 27 Aug 2026 16:49:37 +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=1787849379; cv=none; b=j/5d5AfFBsz/Hpe7jm3YRc36YuxWCD7M4RgHMAdMwI7TLAYApifWOx+SBY1S7m5dkc9JqKVHva+ML+pRA7MfXP9ZDvPkTsywIT8SBF9fnLIKdfe2Sl/iBvbvMkwdiq0rqw/I2JEmYGAMfIzKFk1pee3QiOYKSazMrpQl/2qv6sY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787849379; c=relaxed/simple; bh=3mRnnLbXPK+FL1Y11FZ2tsLwM5/BITjgA8Xy6c7obuU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ju8ZrQ8WhzvV81vzpksH26iJQ7y2CuH7GCwPKoYL1aihxXdFypdQDjhH1+UYKPRf43IA1ImdwzJWN8cq7vTzKeJtRaPEaxR7PhJoDohGdMcTFzLDsmL6SarqIxNNuSFgvnthfrgQLb8rYfFcXL+MP72kUZN/8+gMxs6Km1Lsedk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kGlA7VxW; 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="kGlA7VxW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2378D1F000E9; Thu, 27 Aug 2026 16:49:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787849377; bh=J5cG4iuM1d9Xpr0Ghu/Ar+nS5GiRx98CK/xxd+1xvUA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=kGlA7VxWC4H4LrpdVhC9YYAuk4lfkA5dIfmFjIqZEw/WBSOnbU59U/UDlG3KwPCSA 91i65tzQN9XBNvbBXurAaKaYXesWTyDaeQ4e73MZAK5G+DKufUOg4THZhWZ73Alq3m tbsdvs6Bd1CqbPjnHNRKgIBnjS6Y1dQDikz8Vk1Vo3PFbrOThoqf3Pum/+wRo460Yt Xf1QHoE3boTYnZG9s5GSlBiPYkk8xCbw7jfmYp1ltr/qg5dh5Uh5bPDhvk2bCgJKzd hjIIpnIMUmvxP1fOa2gH1XXK543sCa5MsU2DWLtKzKt7B1TVGz2leERxwjOqlWXA8i ODyD7h1p1IU3Q== Message-ID: Date: Thu, 27 Aug 2026 18:49:33 +0200 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: reject unsupported kmalloc sizes To: Zi Yan , Harry Yoo Cc: Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alan Stern , Greg Kroah-Hartman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, syzbot+805630f1453e490427fa@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20260817-limit_kmalloc_size-v1-1-5bef487701cc@nvidia.com> <82f138f5-11d4-4839-94a3-c226fd982715@kernel.org> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/27/26 17:51, Zi Yan wrote: > On Thu Aug 27, 2026 at 3:47 AM EDT, Vlastimil Babka (SUSE) wrote: >> On 8/26/26 11:52 PM, Zi Yan wrote: >>> On Wed Aug 26, 2026 at 5:47 PM EDT, Harry Yoo wrote: >>>> On Wed, Aug 26, 2026 at 11:28:12AM +0000, Vlastimil Babka (SUSE) wrote: >>>>> On 8/17/26 22:40, Zi Yan wrote: >>>>>> kmalloc is used to allocate physically contiguous memory for kernel >>>>>> allocations. For requests larger than KMALLOC_MAX_CACHE_SIZE, kmalloc uses >>>>>> the page allocator and can only support up to KMALLOC_MAX_SIZE. For request >>>>>> sizes bigger than KMALLOC_MAX_SIZE, the page allocator can emit a WARN >>>>>> because kmalloc allocates an order greater than MAX_PAGE_ORDER. Systems >>>>>> with panic_on_warn=1 crash because of this WARN. Fix it by rejecting any >>>>>> kmalloc size bigger than KMALLOC_MAX_SIZE. >>>>>> >>>>>> Fixes: aadb4bc4a1f9 ("SLUB: direct pass through of page size or higher kmalloc requests") >>>>>> Reported-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com >>>>>> Closes: https://lore.kernel.org/all/6a820ebc.9ebadd4d.20b15e.001b.GAE@google.com/ >>>>>> Tested-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com >>>>>> Signed-off-by: Zi Yan >>>>>> Cc: stable@vger.kernel.org >>>>>> --- >>>>>> It fixes a page allocator warning (order > MAX_PAGE_ORDER) when gadgetfs >>>>>> requests excessively large memory from kmalloc. Instead of adding >>>>>> __GFP_NOWARN to suppress the warning, as was done for usbfs[1], change >>>>>> kmalloc to return NULL without a warning for this specific issue. >>>>>> >>>>>> [1] commit 4f2629ea67e72 ("USB: usbfs: Don't WARN about excessively large memory allocations") >>>>> >>>>> So I checked and for kvmalloc() we have in __kvmalloc_node_noprof() >>>>> >>>>> /* Don't even allow crazy sizes */ >>>>> if (unlikely(size > INT_MAX)) { >>>>> WARN_ON_ONCE(!(flags & __GFP_NOWARN)); >>>>> return NULL; >>>>> } >>>>> >>>>> This comes from Linus in commit 7661809d493b4. I'd do the same thing here >>>>> then. >>>> >>>> But the purpose of this patch is to avoid the warning in the page >>>> allocator. Should we fix this in the caller (gadgetfs) then? >>> >>> It is fixed by: https://lore.kernel.org/all/20260820223719.A4A3C1F000E9@smtp.kernel.org/ >>> >>> Please disregard this patch, but we can keep the discussion going. >> >> I still think this patch has some value if done as proposed above. Yes >> in practice it will just replace the page allocator's warning with a >> different warning, but IMHO it's "nicer" if kmalloc() sanitizes its own > > And SLAB maintainers will be Cc'd. :) For some people it doesn't matter if it's SLAB or PAGE ALLOCATOR :D >> requests to the page allocator, using the KMALLOC_MAX_SIZE value. > > Like this? Or the exact pattern as kvmalloc() is preferred? LGTM. Should return NULL even with __GFP_NOWARN or if the warning has fired and won't again, and AFAICS this does. The kvmalloc() pattern predates WARN_ON_ONCE_GFP addition, I think. > diff --git a/mm/slub.c b/mm/slub.c > index 0337e60db5ace..b562f2a6fbbee 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5263,7 +5263,12 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node) > { > struct page *page; > void *ptr = NULL; > - unsigned int order = get_order(size); > + unsigned int order; > + > + if (WARN_ON_ONCE_GFP(size > KMALLOC_MAX_SIZE, flags)) > + return NULL; > + > + order = get_order(size); > > if (unlikely(flags & GFP_SLAB_BUG_MASK)) > flags = kmalloc_fix_flags(flags); > >