From: Andrea Parri <andrea.pa...@amarulasolutions.com>
[ Upstream commit 09d3f015d1e1b4fee7e9bbdcf54201d239393391 ]
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.pa...@amarulasolutions.com>
Acked-by: Oleg Nesterov <o...@redhat.com>
Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Namhyung Kim <namhy...@kernel.org>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Stephane Eranian <eran...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Vince Weaver <vincent.wea...@maine.edu>
Cc: sta...@kernel.org
Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register()
race")
Link:
http://lkml.kernel.org/r/20181122161031.15179-1-andrea.pa...@amarulasolutions.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
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 4e10bb0b1704..17242c110d1a 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -612,7 +612,7 @@ 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:
@@ -1860,10 +1860,18 @@ 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
