The rseq.h UAPI documents that the rseq_cs field must be cleared before reclaiming memory that contains the targeted struct rseq_cs.
We should extend this comment to also dictate that the rseq_cs field must be cleared before reclaiming memory of the code pointed to by the rseq_cs start_ip and post_commit_offset fields.
While we can expect that use of dlclose(3) will typically unmap both struct rseq_cs and its associated code at once, nothing would theoretically prevent a JIT from reclaiming the code without reclaiming the struct rseq_cs, which would erroneously allow the kernel to consider new code which is not a rseq critical section as a rseq critical section following a code reclaim.
Suggested-by: Florian Weimer fw@deneb.enyo.de Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Florian Weimer fw@deneb.enyo.de Cc: Thomas Gleixner tglx@linutronix.de Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: "Paul E. McKenney" paulmck@linux.ibm.com Cc: Boqun Feng boqun.feng@gmail.com Cc: "H . Peter Anvin" hpa@zytor.com Cc: Paul Turner pjt@google.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Neel Natu neelnatu@google.com Cc: linux-api@vger.kernel.org --- include/uapi/linux/rseq.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h index 9a402fdb60e9..d94afdfc4b7c 100644 --- a/include/uapi/linux/rseq.h +++ b/include/uapi/linux/rseq.h @@ -100,7 +100,9 @@ struct rseq { * instruction sequence block, as well as when the kernel detects that * it is preempting or delivering a signal outside of the range * targeted by the rseq_cs. Also needs to be set to NULL by user-space - * before reclaiming memory that contains the targeted struct rseq_cs. + * before reclaiming memory that contains the targeted struct rseq_cs + * or reclaiming memory that contains the code referred to by the + * start_ip and post_commit_offset fields of struct rseq_cs. * * Read and set by the kernel. Set by user-space with single-copy * atomicity semantics. This field should only be updated by the