4.4-stable review patch. If anyone has any objections, please let me know.
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From: Andrea Parri andrea.parri@amarulasolutions.com
commit 09d3f015d1e1b4fee7e9bbdcf54201d239393391 upstream.
Commit:
142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race")
added the UPROBE_COPY_INSN flag, and corresponding smp_wmb() and smp_rmb() memory barriers, to ensure that handle_swbp() uses fully-initialized uprobes only.
However, the smp_rmb() is mis-placed: this barrier should be placed after handle_swbp() has tested for the flag, thus guaranteeing that (program-order) subsequent loads from the uprobe can see the initial stores performed by prepare_uprobe().
Move the smp_rmb() accordingly. Also amend the comments associated to the two memory barriers to indicate their actual locations.
Signed-off-by: Andrea Parri andrea.parri@amarulasolutions.com Acked-by: Oleg Nesterov oleg@redhat.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Namhyung Kim namhyung@kernel.org Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vincent.weaver@maine.edu Cc: stable@kernel.org Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race") Link: http://lkml.kernel.org/r/20181122161031.15179-1-andrea.parri@amarulasolution... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/events/uprobes.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
--- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -606,7 +606,7 @@ static int prepare_uprobe(struct uprobe BUG_ON((uprobe->offset & ~PAGE_MASK) + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
- smp_wmb(); /* pairs with rmb() in find_active_uprobe() */ + smp_wmb(); /* pairs with the smp_rmb() in handle_swbp() */ set_bit(UPROBE_COPY_INSN, &uprobe->flags);
out: @@ -1892,10 +1892,18 @@ static void handle_swbp(struct pt_regs * * After we hit the bp, _unregister + _register can install the * new and not-yet-analyzed uprobe at the same address, restart. */ - smp_rmb(); /* pairs with wmb() in install_breakpoint() */ if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags))) goto out;
+ /* + * Pairs with the smp_wmb() in prepare_uprobe(). + * + * Guarantees that if we see the UPROBE_COPY_INSN bit set, then + * we must also see the stores to &uprobe->arch performed by the + * prepare_uprobe() call. + */ + smp_rmb(); + /* Tracing handlers use ->utask to communicate with fetch methods */ if (!get_utask()) goto out;