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uprobes: Fix handle_swbp() vs. unregister() + register() race once more 

Commit:

  142b18ddc8 ("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: 142b18ddc8 ("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@kernel.org>
This commit is contained in:
Andrea Parri 2018-11-22 17:10:31 +01:00 committed by Ingo Molnar
parent 472de49fdc
commit 09d3f015d1
1 changed files with 10 additions and 2 deletions
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12
kernel/events/uprobes.c
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@ -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;