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Mon, 17 Aug 2020 14:04:03 -0700 (PDT) Received: from [10.9.0.18] ([185.248.161.177]) by smtp.gmail.com with ESMTPSA id qp16sm15127035ejb.89.2020.08.17.14.03.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Aug 2020 14:04:02 -0700 (PDT) Reply-To: alex.popov@linux.com Subject: Re: [PATCH RFC 1/2] mm: Extract SLAB_QUARANTINE from KASAN To: Pavel Machek , Matthew Wilcox Cc: Kees Cook , Jann Horn , Will Deacon , Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Masahiro Yamada , Masami Hiramatsu , Steven Rostedt , Peter Zijlstra , Krzysztof Kozlowski , Patrick Bellasi , David Howells , Eric Biederman , Johannes Weiner , Laura Abbott , Arnd Bergmann , Greg Kroah-Hartman , kasan-dev@googlegroups.com, linux-mm@kvack.org, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, notify@kernel.org, Andrey Konovalov References: <20200813151922.1093791-1-alex.popov@linux.com> <20200813151922.1093791-2-alex.popov@linux.com> <20200815185455.GB17456@casper.infradead.org> <20200816195930.GA4155@amd> From: Alexander Popov Autocrypt: addr=alex.popov@linux.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200816195930.GA4155@amd> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: ADFAE1801A991 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 16.08.2020 22:59, Pavel Machek wrote: > On Sat 2020-08-15 19:54:55, Matthew Wilcox wrote: >> On Thu, Aug 13, 2020 at 06:19:21PM +0300, Alexander Popov wrote: >>> +config SLAB_QUARANTINE >>> + bool "Enable slab freelist quarantine" >>> + depends on !KASAN && (SLAB || SLUB) >>> + help >>> + Enable slab freelist quarantine to break heap spraying technique >>> + used for exploiting use-after-free vulnerabilities in the kernel >>> + code. If this feature is enabled, freed allocations are stored >>> + in the quarantine and can't be instantly reallocated and >>> + overwritten by the exploit performing heap spraying. >>> + This feature is a part of KASAN functionality. >> >> After this patch, it isn't part of KASAN any more ;-) >> >> The way this is written is a bit too low level. Let's write it in terms >> that people who don't know the guts of the slab allocator or security >> terminology can understand: >> >> Delay reuse of freed slab objects. This makes some security >> exploits harder to execute. It reduces performance slightly >> as objects will be cache cold by the time they are reallocated, >> and it costs a small amount of memory. > > Written this way, it invites questions: > > Does it introduce any new deadlocks in near out-of-memory situations? Linux kernel with enabled KASAN is heavily tested by syzbot. I think Dmitry and Andrey can give good answers to your question. Some time ago I was doing Linux kernel fuzzing with syzkaller on low memory virtual machines (with KASAN and LOCKUP_DETECTOR enabled). I gave less than 1G to each debian stretch VM. I didn't get any special deadlock caused by OOM. Best regards, Alexander