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Date: Sun, 03 Feb 2019 14:45:08 +0100 From: Ben Hutchings <ben@...adent.org.uk> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org CC: akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>, "Andrea Parri" <andrea.parri@...rulasolutions.com>, "Jiri Olsa" <jolsa@...hat.com>, "Arnaldo Carvalho de Melo" <acme@...hat.com>, "Oleg Nesterov" <oleg@...hat.com>, "Vince Weaver" <vincent.weaver@...ne.edu>, "Namhyung Kim" <namhyung@...nel.org>, "Peter Zijlstra" <peterz@...radead.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, "Thomas Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...nel.org>, "Linus Torvalds" <torvalds@...ux-foundation.org>, "Stephane Eranian" <eranian@...gle.com>, "Alexander Shishkin" <alexander.shishkin@...ux.intel.com> Subject: [PATCH 3.16 223/305] uprobes: Fix handle_swbp() vs. unregister() + register() race once more 3.16.63-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Andrea Parri <andrea.parri@...rulasolutions.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@...rulasolutions.com> Acked-by: Oleg Nesterov <oleg@...hat.com> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Arnaldo Carvalho de Melo <acme@...hat.com> Cc: Jiri Olsa <jolsa@...hat.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Namhyung Kim <namhyung@...nel.org> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Stephane Eranian <eranian@...gle.com> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Vince Weaver <vincent.weaver@...ne.edu> Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race") Link: http://lkml.kernel.org/r/20181122161031.15179-1-andrea.parri@amarulasolutions.com Signed-off-by: Ingo Molnar <mingo@...nel.org> Signed-off-by: Ben Hutchings <ben@...adent.org.uk> --- kernel/events/uprobes.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -610,7 +610,7 @@ 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: @@ -1858,10 +1858,18 @@ 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;
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