Re: [PATCH 0/2] tracing: Detect unsafe dereferencing of pointers from trace events
From: Steven Rostedt
Date: Sat Feb 27 2021 - 19:22:24 EST
[ Resending with an address that should work for Felipe ]
On 2021年2月27日 14:18:02 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
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On 2021年2月26日 14:21:00 -0800
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Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
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> On Fri, Feb 26, 2021 at 11:07 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
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> >
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> > The first patch scans the print fmts of the trace events looking for
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> > dereferencing pointers from %p*, and making sure that they refer back
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> > to the trace event itself.
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> >
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> > The second patch handles strings "%s" [..]
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> Doing this at runtime really feels like the wrong thing to do.
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> It won't even protect us from what happened - people like me and
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> Andrew won't even run those tracepoints in the first place, so we
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> won't notice.
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> It really would be much better in every respect to have this done by
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> checkpatch, I think.
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And after fixing the parsing to not trigger false positives, an
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allyesconfig boot found this:
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event cdns3_gadget_giveback has unsafe dereference of argument 11
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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,
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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
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C->stream_id
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(as the above is from a trace event class, it triggered for every event
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in that class).
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As it looks like it uses %pa which IIUC from the printk code, it
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dereferences the pointer to find it's virtual address. The event has
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this as the field:
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__field(struct cdns3_trb *, start_trb_addr)
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Assigns it with:
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__entry->start_trb_addr = req->trb;
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And prints that with %pa, which will dereference pointer at the time of
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reading, where the address in question may no longer be around. That
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looks to me as a potential bug.
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[ Cc'd the people responsible for that code. ]
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-- Steve