Messages in this thread Patch in this message | | | From | Mathieu Desnoyers <> | Subject | [PATCH for 5.5 1/2] rseq: Fix: Clarify rseq.h UAPI rseq_cs memory reclaim requirements | Date | Fri, 20 Dec 2019 15:12:06 -0500 |
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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..6f26b0b148a6 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 refered 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
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