----- On Jun 22, 2022, at 3:46 PM, Mathieu Desnoyers mathieu.desnoyers@xxxxxxxxxxxx wrote: > 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. Hi Peter, would you consider pulling this patch through the tip tree ? Thanks, Mathieu > > Link: > https://lore.kernel.org/lkml/20220618182515.95831-1-minhquangbui99@xxxxxxxxx/ > [1] > Link: > https://lore.kernel.org/lkml/258546133.12151.1655739550814.JavaMail.zimbra@xxxxxxxxxxxx/ > [2] > Link: > https://lore.kernel.org/lkml/87pmj1enjh.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ [3] > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > --- > 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 <trace/events/rseq.h> > > -#define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE | \ > - 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) > > /* > * > @@ -175,23 +176,15 @@ static int rseq_need_restart(struct task_struct *t, u32 > cs_flags) > u32 flags, event_mask; > int ret; > > + if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS)) > + return -EINVAL; > + > /* Get thread flags. */ > ret = get_user(flags, &t->rseq->flags); > if (ret) > return ret; > > - /* Take critical section flags into account. */ > - flags |= 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) != > - RSEQ_CS_PREEMPT_MIGRATE_FLAGS)) > + if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS)) > return -EINVAL; > > /* > @@ -203,7 +196,7 @@ static int rseq_need_restart(struct task_struct *t, u32 > cs_flags) > t->rseq_event_mask = 0; > preempt_enable(); > > - return !!(event_mask & ~flags); > + return !!event_mask; > } > > static int clear_rseq_cs(struct task_struct *t) > -- > 2.30.2 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
