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id CBEA8AD6B; Thu, 5 Sep 2019 08:03:28 +0000 (UTC) Subject: Re: [PATCH 1/2] mm/kasan: dump alloc/free stack for page allocator To: Walter Wu Cc: Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , Matthias Brugger , Andrew Morton , Martin Schwidefsky , Arnd Bergmann , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com References: <20190904065133.20268-1-walter-zh.wu@mediatek.com> <401064ae-279d-bef3-a8d5-0fe155d0886d@suse.cz> <1567605965.32522.14.camel@mtksdccf07> <7998e8f1-e5e2-da84-ea1f-33e696015dce@suse.cz> <1567607063.32522.24.camel@mtksdccf07> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= mQINBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 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2ijoaMFTAU+uBtE14UP5F+LWdmRdEGS1Ah1NwooL27uAFllTDQxDhg/+LJ/TqB8ZuidOIy1B xVKRSg3I2m+DUTVqBy7Lixo73hnW69kSjtqCeamY/NSu6LNP+b0wAOKhwz9hBEwEHLp05+mj 5ZFJyfGsOiNUcMoO/17FO4EBxSDP3FDLllpuzlFD7SXkfJaMWYmXIlO0jLzdfwfcnDzBbPwO hBM8hvtsyq8lq8vJOxv6XD6xcTtj5Az8t2JjdUX6SF9hxJpwhBU0wrCoGDkWp4Bbv6jnF7zP Nzftr4l8RuJoywDIiJpdaNpSlXKpj/K6KrnyAI/joYc7 Message-ID: <99913463-0e2c-7dab-c1eb-8b9e149b3ee3@suse.cz> Date: Thu, 5 Sep 2019 10:03:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1567607063.32522.24.camel@mtksdccf07> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/4/19 4:24 PM, Walter Wu wrote: > On Wed, 2019-09-04 at 16:13 +0200, Vlastimil Babka wrote: >> On 9/4/19 4:06 PM, Walter Wu wrote: >> >> The THP fix is not required for the rest of the series, it was even merged to >> mainline separately. >> >>> And It looks like something is different, because we only need last >>> stack of page, so it can decrease memory overhead. >> >> That would save you depot_stack_handle_t (which is u32) per page. I guess that's >> nothing compared to KASAN overhead? >> > If we can use less memory, we can achieve what we want. Why not? In my experience to solve some UAFs, it's important to know not only the freeing stack, but also the allocating stack. Do they make sense together, or not? In some cases, even longer history of alloc/free would be nice :) Also by simply recording the free stack in the existing depot handle, you might confuse existing page_owner file consumers, who won't know that this is a freeing stack. All that just doesn't seem to justify saving an u32 per page. > Thanks. > Walter > > >