Re: [PATCH] objtool,x86: Verify poke_int3_handler() is self contained

Ingo Molnar
2020-07-27T11:21:50Z

* peterz@infradead.org <peterz@infradead.org> wrote:

>
> Abuse the SMAP rules to ensure poke_int3_handler() doesn't call out to
> anything.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> tools/objtool/check.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -551,6 +551,14 @@ static const char *uaccess_safe_builtin[
> "__memcpy_mcsafe",
> "mcsafe_handle_tail",
> "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
> + /*
> + * Abuse alert!
> + *
> + * poke_int3_handler() is not in fact related to uaccess at all, we
> + * abuse the uaccess rules to ensure poke_int3_handler() is self
> + * contained and doesn't CALL out to other code.
> + */
> + "poke_int3_handler",

So ->uaccess_safe makes sure that we don't CALL into non-uaccess-safe
functions, but it still allows CALLs into *other* uaccess-safe
functions, right?

So unless I missed something in the logic, the comment should say
something like "doesn't CALL out to other non-uaccess safe code" or
so? Which is, arguably, like 99% of all functions - but still, a whole
bunch are allowed, such as low level instrumentation and other utility
functions.

Thanks,

Ingo