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McKenney" , Boqun Feng , "H . Peter Anvin" , Paul Turner , linux-api@vger.kernel.org, Peter Oskolkov , Mathieu Desnoyers Subject: [PATCH 1/2] rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags Date: Wed, 22 Jun 2022 15:46:16 -0400 Message-Id: <20220622194617.1155957-1-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The pretty much unused RSEQ_CS_FLAG_NO_RESTART_ON_* flags introduce complexity in rseq, and are subtly buggy [1]. Solving those issues requires introducing additional complexity in the rseq implementation for each supported architecture. Considering that it complexifies the rseq ABI, I am proposing that we deprecate those flags. [2] So far there appears to be consensus from maintainers of user-space projects impacted by this feature that its removal would be a welcome simplification. [3] The deprecation approach proposed here is to issue WARN_ON_ONCE() when encountering those flags and kill the offending process with sigsegv. This should allow us to quickly identify whether anyone yells at us for removing this. Link: https://lore.kernel.org/lkml/20220618182515.95831-1-minhquangbui99@= gmail.com/ [1] Link: https://lore.kernel.org/lkml/258546133.12151.1655739550814.JavaMail= .zimbra@efficios.com/ [2] Link: https://lore.kernel.org/lkml/87pmj1enjh.fsf@email.froward.int.ebied= erm.org/ [3] Signed-off-by: Mathieu Desnoyers --- kernel/rseq.c | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-) diff --git a/kernel/rseq.c b/kernel/rseq.c index 97ac20b4f738..81d7dc80787b 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -18,8 +18,9 @@ #define CREATE_TRACE_POINTS #include =20 -#define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRAT= E | \ - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT) +#define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \ + RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \ + RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE) =20 /* * @@ -175,23 +176,15 @@ static int rseq_need_restart(struct task_struct *t,= u32 cs_flags) u32 flags, event_mask; int ret; =20 + if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS)) + return -EINVAL; + /* Get thread flags. */ ret =3D get_user(flags, &t->rseq->flags); if (ret) return ret; =20 - /* Take critical section flags into account. */ - flags |=3D cs_flags; - - /* - * Restart on signal can only be inhibited when restart on - * preempt and restart on migrate are inhibited too. Otherwise, - * a preempted signal handler could fail to restart the prior - * execution context on sigreturn. - */ - if (unlikely((flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL) && - (flags & RSEQ_CS_PREEMPT_MIGRATE_FLAGS) !=3D - RSEQ_CS_PREEMPT_MIGRATE_FLAGS)) + if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS)) return -EINVAL; =20 /* @@ -203,7 +196,7 @@ static int rseq_need_restart(struct task_struct *t, u= 32 cs_flags) t->rseq_event_mask =3D 0; preempt_enable(); =20 - return !!(event_mask & ~flags); + return !!event_mask; } =20 static int clear_rseq_cs(struct task_struct *t) --=20 2.30.2