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Mon, 17 Aug 2020 13:34:23 -0700 (PDT) Received: from [10.9.0.18] ([185.248.161.177]) by smtp.gmail.com with ESMTPSA id r11sm31238821wrw.78.2020.08.17.13.34.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Aug 2020 13:34:21 -0700 (PDT) Reply-To: alex.popov@linux.com Subject: Re: [PATCH RFC 1/2] mm: Extract SLAB_QUARANTINE from KASAN To: 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 References: <20200813151922.1093791-1-alex.popov@linux.com> <20200813151922.1093791-2-alex.popov@linux.com> <20200815185455.GB17456@casper.infradead.org> 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: <20200815185455.GB17456@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E3C1718086CDA X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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 15.08.2020 21:54, 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 ;-) Ok, I'll change that to "this feature is used by KASAN" :) > 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. > > (feel free to edit this) Ok, I see. I'll start from high-level description and add low-level details at the end. >> +struct qlist_node { >> + struct qlist_node *next; >> +}; > > I appreciate this isn't new, but why do we have a new singly-linked-list > abstraction being defined in this code? I don't know for sure. I suppose it is caused by SLAB/SLUB freelist implementation details (qlist_node in kasan_free_meta is also used for the allocator freelist). Best regards, Alexander