x86/ibt, objtool: Don't discard text references from tracepoint section

x86/ibt, objtool: Don't discard text references from tracepoint section

On Tue, Jun 28, 2022 at 04:28:58PM +0800, Pengfei Xu wrote:

> # ./ftracetest
> === Ftrace unit tests ===
> [1] Basic trace file check      [PASS]
> [2] Basic test for tracers      [PASS]
> [3] Basic trace clock test      [PASS]
> [4] Basic event tracing check   [PASS]
> [5] Change the ringbuffer size  [PASS]
> [6] Snapshot and tracing setting        [PASS]
> [7] trace_pipe and trace_marker [PASS]
> [8] Test ftrace direct functions against tracers        [UNRESOLVED]
> [9] Test ftrace direct functions against kprobes        [UNRESOLVED]
> [10] Generic dynamic event - add/remove eprobe events   [FAIL]
> [11] Generic dynamic event - add/remove kprobe events
>
> It 100% reproduced in step 11 and then missing ENDBR BUG generated:
> "
> [ 9332.752836] mmiotrace: enabled CPU7.
> [ 9332.788612] mmiotrace: disabled.
> [ 9337.103426] traps: Missing ENDBR: syscall_regfunc+0x0/0xb0

It turns out that while syscall_regfunc() does have an ENDBR when
generated, it gets sealed by objtool's .ibt_endbr_seal list.

Since the only text references to this function:

  $ git grep syscall_regfunc
  include/linux/tracepoint.h:extern int syscall_regfunc(void);
  include/trace/events/syscalls.h:        syscall_regfunc, syscall_unregfunc
  include/trace/events/syscalls.h:        syscall_regfunc, syscall_unregfunc
  kernel/tracepoint.c:int syscall_regfunc(void)

appear in the __tracepoint section which is excluded by objtool.

Fixes: 3c6f9f77e618 ("objtool: Rework ibt and extricate from stack validation")
Reported-by: Pengfei Xu <pengfei.xu@intel.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Yrrepdaow4F5kqG0@hirez.programming.kicks-ass.net