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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 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 X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9687840002 X-Stat-Signature: nrjstx8y15mzferrgd1rzab7xuca9nq9 X-HE-Tag: 1787849378-411583 X-HE-Meta: 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 LlBsVPqQ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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); > >