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authentication-results: spf=none (sender IP is ) smtp.mailfrom=Alexander.Levin@microsoft.com; x-microsoft-antispam-message-info: tgcRJGXz0fTQULr6qomu73P7jaCxslstCOhqM8LWHYGI3lR8LWAlVFGIFySV9/a+psOi7vCgOoRf7HzCAOJMSmZy48Hb1VA7hJSQHcJNT3BGPNPspoAgOOwkN1Dx9xGonxXa35KTH4JJAP4JF2ClsYqkhEOPev4q5+p0OGyZuTXo6jbqiqu38lM1yzsQ2sgNuM0vc/0QaEW4vf//KC0Pbp14WmwZnM8C4P/N0UbkX7RnI4/AYGsN11tifdqImrjHsJxuMwqsVyS9Nd8DgHPfYmjMYzdTDbRoQSdwwb600wa9NIiSnUfpJy6Wg2U44lmxNiDHe88vKTL4hb1yy3AwuA== spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9af78896-12f2-4b51-b306-08d58db23ee0 X-MS-Exchange-CrossTenant-originalarrivaltime: 19 Mar 2018 15:58:23.9590 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB0933 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Will Deacon [ Upstream commit 88b0193d9418c00340e45e0a913a0813bc6c8c96 ] Perf can generate and record a user callchain in response to a synchronous request, such as a tracepoint firing. If this happens under set_fs(KERNEL_D= S), then we can end up walking the user stack (and dereferencing/saving whateve= r we find there) without the protections usually afforded by checks such as access_ok. Rather than play whack-a-mole with each architecture's stack unwinding implementation, fix the root of the problem by ensuring that we force USER_= DS when invoking perf_callchain_user from the perf core. Reported-by: Al Viro Signed-off-by: Will Deacon Acked-by: Peter Zijlstra Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Thomas Gleixner Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/events/callchain.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index e9fdb5203de5..411226b26bca 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -227,12 +227,18 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr,= bool kernel, bool user, } =20 if (regs) { + mm_segment_t fs; + if (crosstask) goto exit_put; =20 if (add_mark) perf_callchain_store_context(&ctx, PERF_CONTEXT_USER); + + fs =3D get_fs(); + set_fs(USER_DS); perf_callchain_user(&ctx, regs); + set_fs(fs); } } =20 --=20 2.14.1