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0031-rseq-Deprecate-RSEQ_CS_FLAG_NO_RESTART_ON_-flags.patch
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0031-rseq-Deprecate-RSEQ_CS_FLAG_NO_RESTART_ON_-flags.patch
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From 0190e4198e47fe99d002d72588f34fd62c9ab570 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <[email protected]>
Date: Wed, 22 Jun 2022 15:46:16 -0400
Subject: [PATCH 31/32] rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags
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/[email protected]/ [1]
Link: https://lore.kernel.org/lkml/[email protected]/ [2]
Link: https://lore.kernel.org/lkml/[email protected]/ [3]
Signed-off-by: Mathieu Desnoyers <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]
---
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)
--
2.37.1