Re: [PATCH for 5.5 1/2 v2] rseq: Fix: Clarify rseq.h UAPI rseq_cs memory reclaim requirements
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From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2020-01-06 19:10:41
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----- On Dec 20, 2019, at 3:33 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
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.
Hi Peter, Is there anything preventing this rseq UAPI documentation fix from being merged ? Thanks, Mathieu
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Suggested-by: Florian Weimer <redacted> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Florian Weimer <redacted> Cc: Thomas Gleixner <redacted> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: "Paul E. McKenney" <redacted> Cc: Boqun Feng <redacted> Cc: "H . Peter Anvin" <hpa@zytor.com> Cc: Paul Turner <redacted> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Neel Natu <redacted> 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 -- 2.17.1
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com