Messages in this thread | | | Date | Thu, 22 Nov 2018 17:19:42 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] uprobes: Fix handle_swbp() vs. unregister() + register() race once more |
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On 11/22, Andrea Parri wrote: > > 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> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Oleg Nesterov <oleg@redhat.com> > Cc: stable@kernel.org > Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race")
Thanks,
Acked-by: Oleg Nesterov <oleg@redhat.com>
> --- > kernel/events/uprobes.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 96d4bee83489b..322e97bbb4370 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -829,7 +829,7 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file, > 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: > @@ -2178,10 +2178,18 @@ static void handle_swbp(struct pt_regs *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; > -- > 2.17.1 >
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