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Mon, 11 Dec 2023 02:46:58 -0800 (PST) MIME-Version: 1.0 References: <20231121220155.1217090-1-iii@linux.ibm.com> <20231121220155.1217090-31-iii@linux.ibm.com> In-Reply-To: <20231121220155.1217090-31-iii@linux.ibm.com> From: Alexander Potapenko Date: Mon, 11 Dec 2023 11:46:22 +0100 Message-ID: Subject: Re: [PATCH v2 30/33] s390/uaccess: Add KMSAN support to put_user() and get_user() To: Ilya Leoshkevich Cc: Alexander Gordeev , Andrew Morton , Christoph Lameter , David Rientjes , Heiko Carstens , Joonsoo Kim , Marco Elver , Masami Hiramatsu , Pekka Enberg , Steven Rostedt , Vasily Gorbik , Vlastimil Babka , Christian Borntraeger , Dmitry Vyukov , Hyeonggon Yoo <42.hyeyoo@gmail.com>, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Mark Rutland , Roman Gushchin , Sven Schnelle Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: B30AD14000B X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: a3nbths7hgr64gemmq39sc5ke9apsoqq X-HE-Tag: 1702291619-376826 X-HE-Meta: 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 JPCTdwGV +/cZIdsB7VnqVKmD1sYVI1PJbz/yCILBU963nZZdrDURLBLyNqYLpFiwvEaJx8npalhO4Eu3iHHAwfDfUq1DD4hYcjqanU/iPgAOgLyKJDwt8An2OR1qwaSHz51Ix/FfgCQ0L9wTTzDEmAI0c4H40if6HdQ1YdryBjkYcicxUajYxswUW+y5GaAjewRWqqp8sx3ZqLxvn/hNml1GYhKTd1VHaQGB7J5g9nxUxiVRCAFJvb2LR80jVIbk4DGClusfoCzLczFnTjcCTqrMw7hihgMwSXT8tlXADSiVB1yEUhoT5I2SbnUZvyU6BLEn2XzqjawDK6b9UsYYjD0pgINCocPrEYVP1ARawlweBsGttff2VOec= X-Bogosity: Ham, tests=bogofilter, spamicity=0.003370, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Nov 21, 2023 at 11:03=E2=80=AFPM Ilya Leoshkevich wrote: > > put_user() uses inline assembly with precise constraints, so Clang is > in principle capable of instrumenting it automatically. Unfortunately, > one of the constraints contains a dereferenced user pointer, and Clang > does not currently distinguish user and kernel pointers. Therefore > KMSAN attempts to access shadow for user pointers, which is not a right > thing to do. > > An obvious fix to add __no_sanitize_memory to __put_user_fn() does not > work, since it's __always_inline. And __always_inline cannot be removed > due to the __put_user_bad() trick. > > A different obvious fix of using the "a" instead of the "+Q" constraint > degrades the code quality, which is very important here, since it's a > hot path. > > Instead, repurpose the __put_user_asm() macro to define > __put_user_{char,short,int,long}_noinstr() functions and mark them with > __no_sanitize_memory. For the non-KMSAN builds make them > __always_inline in order to keep the generated code quality. Also > define __put_user_{char,short,int,long}() functions, which call the > aforementioned ones and which *are* instrumented, because they call > KMSAN hooks, which may be implemented as macros. > > The same applies to get_user() as well. > > Acked-by: Heiko Carstens > Signed-off-by: Ilya Leoshkevich I think this patch makes sense, but I don't feel myself qualified enough to stamp it. Hope Heiko's ack is enough.