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rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags

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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.ebiederm.org/ [3]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/lkml/20220622194617.1155957-1-mathieu.desnoyers@efficios.com
This commit is contained in:
Mathieu Desnoyers 2022-06-22 15:46:16 -04:00 committed by Ingo Molnar
parent 91caa5ae24
commit 0190e4198e
1 changed files with 8 additions and 15 deletions
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23
kernel/rseq.c
View File

@ -18,8 +18,9 @@
#define CREATE_TRACE_POINTS #define CREATE_TRACE_POINTS
#include <trace/events/rseq.h> #include <trace/events/rseq.h>
#define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE | \ #define RSEQ_CS_NO_RESTART_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT | \
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; u32 flags, event_mask;
int ret; int ret;
if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS))
return -EINVAL;
/* Get thread flags. */ /* Get thread flags. */
ret = get_user(flags, &t->rseq->flags); ret = get_user(flags, &t->rseq->flags);
if (ret) if (ret)
return ret; return ret;
/* Take critical section flags into account. */ if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS))
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))
return -EINVAL; return -EINVAL;
/* /*
@ -203,7 +196,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
t->rseq_event_mask = 0; t->rseq_event_mask = 0;
preempt_enable(); preempt_enable();
return !!(event_mask & ~flags); return !!event_mask;
} }
static int clear_rseq_cs(struct task_struct *t) static int clear_rseq_cs(struct task_struct *t)