perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set
authorJiri Olsa <jolsa@kernel.org>
Mon, 27 Aug 2018 09:12:25 +0000 (11:12 +0200)
committerArnaldo Carvalho de Melo <acme@redhat.com>
Thu, 30 Aug 2018 17:49:23 +0000 (14:49 -0300)
We need to change the breakpoint even if the attr with new fields has
disabled set to true.

Current code prevents following user code to change the breakpoint
address:

  ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[0]), addr_1)
  ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[0]), addr_2)
  ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[7]), dr7)

The first PTRACE_POKEUSER creates the breakpoint with attr.disabled set
to true:

  ptrace_set_breakpoint_addr(nr = 0)
    struct perf_event *bp = t->ptrace_bps[nr];

    ptrace_register_breakpoint(..., disabled = true)
      ptrace_fill_bp_fields(..., disabled)
      register_user_hw_breakpoint

So the second PTRACE_POKEUSER will be omitted:

  ptrace_set_breakpoint_addr(nr = 0)
    struct perf_event *bp = t->ptrace_bps[nr];
    struct perf_event_attr attr = bp->attr;

    modify_user_hw_breakpoint(bp, &attr)
      if (!attr->disabled)
        modify_user_hw_breakpoint_check

Reported-by: Milind Chabbi <chabbi.milind@gmail.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180827091228.2878-3-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
kernel/events/hw_breakpoint.c

index b3814fce5ecb6bf7729ea858ec17ddb9018105f1..fb229d9c7f3c9437866638cfec5705af73ba3733 100644 (file)
@@ -509,6 +509,8 @@ modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *a
  */
 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 {
+       int err;
+
        /*
         * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
         * will not be possible to raise IPIs that invoke __perf_event_disable.
@@ -520,11 +522,11 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
        else
                perf_event_disable(bp);
 
-       if (!attr->disabled) {
-               int err = modify_user_hw_breakpoint_check(bp, attr, false);
+       err = modify_user_hw_breakpoint_check(bp, attr, false);
+       if (err)
+               return err;
 
-               if (err)
-                       return err;
+       if (!attr->disabled) {
                perf_event_enable(bp);
                bp->attr.disabled = 0;
        }