Messages in this thread | | | Date | Tue, 2 Mar 2021 16:23:55 +0800 | From | Peter Chen <> | Subject | Re: [PATCH 0/2] tracing: Detect unsafe dereferencing of pointers from trace events |
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On 21-03-01 05:27:04, Pawel Laszczak wrote: > > + Peter Chen - Maintainer of CDNS3 driver > > > > >[ Resending with an address that should work for Felipe ] > > > >On Sat, 27 Feb 2021 14:18:02 -0500 > >Steven Rostedt <rostedt@goodmis.org> wrote: > > > >> On Fri, 26 Feb 2021 14:21:00 -0800 > >> Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> > >> > On Fri, Feb 26, 2021 at 11:07 AM Steven Rostedt <rostedt@goodmis.org> wrote: > >> > > > >> > > The first patch scans the print fmts of the trace events looking for > >> > > dereferencing pointers from %p*, and making sure that they refer back > >> > > to the trace event itself. > >> > > > >> > > The second patch handles strings "%s" [..] > >> > > >> > Doing this at runtime really feels like the wrong thing to do. > >> > > >> > It won't even protect us from what happened - people like me and > >> > Andrew won't even run those tracepoints in the first place, so we > >> > won't notice. > >> > > >> > It really would be much better in every respect to have this done by > >> > checkpatch, I think. > >> > >> And after fixing the parsing to not trigger false positives, an > >> allyesconfig boot found this: > >> > >> event cdns3_gadget_giveback has unsafe dereference of argument 11 > >> print_fmt: "%s: req: %p, req buff %p, length: %u/%u %s%s%s, status: %d, trb: [start:%d, end:%d: virt addr %pa], flags:%x SID: %u", > >__get_str(name), REC->req, REC->buf, > >> REC->actual, REC->length, REC->zero ? "Z" : "z", REC->short_not_ok ? "S" : "s", REC->no_interrupt ? "I" : "i", REC->status, REC- > >>start_trb, REC->end_trb, REC->start_trb_addr, REC->flags, RE > >> C->stream_id > >> > >> (as the above is from a trace event class, it triggered for every event > >> in that class). > >> > >> As it looks like it uses %pa which IIUC from the printk code, it > >> dereferences the pointer to find it's virtual address. The event has > >> this as the field: > >> > >> __field(struct cdns3_trb *, start_trb_addr) > >> > >> Assigns it with: > >> > >> __entry->start_trb_addr = req->trb; > >> > >> And prints that with %pa, which will dereference pointer at the time of > >> reading, where the address in question may no longer be around. That > >> looks to me as a potential bug.
Steven, thanks for reporting. Do you mind sending patch to fix it? If you have no time to do it, I will do it later.
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Thanks, Peter Chen
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