The rseq.h UAPI now documents that the rseq_cs field must be cleared before reclaiming memory that contains the targeted struct rseq_cs, but also 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: Shuah Khan skhan@linuxfoundation.org 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 --- tools/testing/selftests/rseq/rseq.h | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h index d40d60e7499e..3f63eb362b92 100644 --- a/tools/testing/selftests/rseq/rseq.h +++ b/tools/testing/selftests/rseq/rseq.h @@ -149,11 +149,13 @@ static inline void rseq_clear_rseq_cs(void) /* * rseq_prepare_unload() should be invoked by each thread executing a rseq * critical section at least once between their last critical section and - * library unload of the library defining the rseq critical section - * (struct rseq_cs). This also applies to use of rseq in code generated by - * JIT: rseq_prepare_unload() should be invoked at least once by each - * thread executing a rseq critical section before reclaim of the memory - * holding the struct rseq_cs. + * library unload of the library defining the rseq critical section (struct + * rseq_cs) or the code referred to by the struct rseq_cs start_ip and + * post_commit_offset fields. This also applies to use of rseq in code + * generated by JIT: rseq_prepare_unload() should be invoked at least once by + * each thread executing a rseq critical section before reclaim of the memory + * holding the struct rseq_cs or reclaim of the code pointed to by struct + * rseq_cs start_ip and post_commit_offset fields. */ static inline void rseq_prepare_unload(void) {