[kernel-hardening] Re: [PATCH 3/3] trace: print address if symbol not found

Steven Rostedt
2017-12-18T16:49:47Z

On Mon, 18 Dec 2017 10:53:32 +1100
"Tobin C. Harding" <me@tobin.cc> wrote:

> Fixes behaviour modified by: commit bd6b239cdbb2 ("kallsyms: don't leak
> address when symbol not found")
>
> Previous patch changed behaviour of kallsyms function sprint_symbol() to
> return an error code instead of printing the address if a symbol was not
> found. Ftrace relies on the original behaviour. We should not break
> tracing when applying the previous patch. We can maintain the original
> behaviour by checking the return code on calls to sprint_symbol() and
> friends.
>
> Check return code and print actual address on error (i.e symbol not
> found).
>
> Signed-off-by: Tobin C. Harding <me@tobin.cc>
> ---
> kernel/trace/trace.h | 24 ++++++++++++++++++++++++
> kernel/trace/trace_events_hist.c | 6 +++---
> 2 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 2a6d0325a761..881b1a577d75 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1814,4 +1814,28 @@ static inline void trace_event_eval_update(struct trace_eval_map **map, int len)
>
> extern struct trace_iterator *tracepoint_print_iter;
>
> +static inline int
> +trace_sprint_symbol(char *buffer, unsigned long address)
> +{
> + int ret;
> +
> + ret = sprint_symbol(buffer, address);
> + if (ret == -1)
> + ret = sprintf(buffer, "0x%lx", address);
> +
> + return ret;
> +}
> +
> +static inline int
> +trace_sprint_symbol_no_offset(char *buffer, unsigned long address)
> +{
> + int ret;
> +
> + ret = sprint_symbol_no_offset(buffer, address);
> + if (ret == -1)
> + ret = sprintf(buffer, "0x%lx", address);
> +
> + return ret;
> +}
> +
> #endif /* _LINUX_KERNEL_TRACE_H */
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 1e1558c99d56..3e28522a76f4 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -982,7 +982,7 @@ static void hist_trigger_stacktrace_print(struct seq_file *m,
> return;
>
> seq_printf(m, "%*c", 1 + spaces, ' ');
> - sprint_symbol(str, stacktrace_entries[i]);
> + trace_sprint_symbol_addr(str, stacktrace_entries[i]);

Hmm, where is trace_sprint_symbol_addr() defined?

-- Steve

> seq_printf(m, "%s\n", str);
> }
> }
> @@ -1014,12 +1014,12 @@ hist_trigger_entry_print(struct seq_file *m,
> seq_printf(m, "%s: %llx", field_name, uval);
> } else if (key_field->flags & HIST_FIELD_FL_SYM) {
> uval = *(u64 *)(key + key_field->offset);
> - sprint_symbol_no_offset(str, uval);
> + trace_sprint_symbol_no_offset(str, uval);
> seq_printf(m, "%s: [%llx] %-45s", field_name,
> uval, str);
> } else if (key_field->flags & HIST_FIELD_FL_SYM_OFFSET) {
> uval = *(u64 *)(key + key_field->offset);
> - sprint_symbol(str, uval);
> + trace_sprint_symbol(str, uval);
> seq_printf(m, "%s: [%llx] %-55s", field_name,
> uval, str);
> } else if (key_field->flags & HIST_FIELD_FL_EXECNAME) {