On Tue, 23 Feb 2021 at 16:16, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
On Tue, Feb 23, 2021 at 4:10 PM 'Marco Elver' via kasan-dev
<kasan-dev@xxxxxxxxxxxxxxxx> wrote:
Encode information from breakpoint attributes into siginfo_t, which
helps disambiguate which breakpoint fired.
Note, providing the event fd may be unreliable, since the event may have
been modified (via PERF_EVENT_IOC_MODIFY_ATTRIBUTES) between the event
triggering and the signal being delivered to user space.
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
---
kernel/events/core.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 8718763045fd..d7908322d796 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6296,6 +6296,17 @@ static void perf_sigtrap(struct perf_event *event)
info.si_signo = SIGTRAP;
info.si_code = TRAP_PERF;
info.si_errno = event->attr.type;
+
+ switch (event->attr.type) {
+ case PERF_TYPE_BREAKPOINT:
+ info.si_addr = (void *)(unsigned long)event->attr.bp_addr;
+ info.si_perf = (event->attr.bp_len << 16) | (u64)event->attr.bp_type;
+ break;
+ default:
+ /* No additional info set. */
Should we prohibit using attr.sigtrap for !PERF_TYPE_BREAKPOINT if we
don't know what info to pass yet?
I don't think it's necessary. This way, by default we get support for
other perf events. If user space observes si_perf==0, then there's no
information available. That would require that any event type that
sets si_perf in future, must ensure that it sets si_perf!=0.
I can add a comment to document the requirement here (and user space
facing documentation should get a copy of how the info is encoded,
too).
Alternatively, we could set si_errno to 0 if no info is available, at
the cost of losing the type information for events not explicitly
listed here.
Note that PERF_TYPE_HARDWARE == 0, so setting si_errno to 0 does not
work. Which leaves us with:
1. Ensure si_perf==0 (or some other magic value) if no info is
available and !=0 otherwise.
2. Return error for events where we do not officially support
requesting sigtrap.
I'm currently leaning towards (1).
What do you prefer?
Ah, I see.
Let's wait for the opinions of other people. There are a number of
options for how to approach this.
