hw_breakpoint: Add perf_event_attr fields check in __modify_user_hw_breakpoint()

And rename it to modify_user_hw_breakpoint_check().

We are about to use modify_user_hw_breakpoint_check() for user space
breakpoints modification, we must be very strict to check only the
fields we can change have changed. As Peter explained:

 "Suppose someone does:

        attr = malloc(sizeof(*attr)); // uninitialized memory
        attr->type = BP;
        attr->bp_addr = new_addr;
        attr->bp_type = bp_type;
        attr->bp_len = bp_len;
        ioctl(fd, PERF_IOC_MOD_ATTR, &attr);

  And feeds absolute shite for the rest of the fields.
  Then we later want to extend IOC_MOD_ATTR to allow changing
  attr::sample_type but we can't, because that would break the
  above application."

I'm making this check optional because we already export
modify_user_hw_breakpoint() and with this check we could
break existing users.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Milind Chabbi <chabbi.milind@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <onestero@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20180312134548.31532-6-jolsa@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index a556aba223da..0c82663395f7 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -456,7 +456,9 @@ register_user_hw_breakpoint(struct perf_event_attr *attr,
 }
 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 
-static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
+static int
+modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
+                                bool check)
 {
         u64 old_addr = bp->attr.bp_addr;
         u64 old_len  = bp->attr.bp_len;
@@ -468,6 +470,9 @@ static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_
         bp->attr.bp_type = attr->bp_type;
         bp->attr.bp_len  = attr->bp_len;
 
+        if (check && memcmp(&bp->attr, attr, sizeof(*attr)))
+                return -EINVAL;
+
         err = validate_hw_breakpoint(bp);
         if (!err && modify)
                 err = modify_bp_slot(bp, old_type);
@@ -505,7 +510,7 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
         else
                 perf_event_disable(bp);
 
-        err = __modify_user_hw_breakpoint(bp, attr);
+        err = modify_user_hw_breakpoint_check(bp, attr, false);
 
         if (err) {
                 if (!bp->attr.disabled)