Re: [PATCH v3 11/17] arm64: disable function graph tracing with SCS

Kees Cook
2019-11-01T03:58:21Z

On Thu, Oct 31, 2019 at 09:46:31AM -0700, samitolvanen@google.com wrote:
> With CONFIG_FUNCTION_GRAPH_TRACER, function return addresses are
> modified in ftrace_graph_caller and prepare_ftrace_return to redirect
> control flow to ftrace_return_to_handler. This is incompatible with
> SCS.

IIRC, the argument was to disable these on a per-arch basis instead of
doing it as a "depends on !SHADOW_CALL_STACK" in the top-level function
graph tracer Kconfig? (I'm just thinking ahead to doing this again for
other architectures, though, I guess, there is much more work than just
that for, say, x86.)

Regardless:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
> arch/arm64/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index e7b57a8a5531..42867174920f 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -148,7 +148,7 @@ config ARM64
> select HAVE_FTRACE_MCOUNT_RECORD
> select HAVE_FUNCTION_TRACER
> select HAVE_FUNCTION_ERROR_INJECTION
> - select HAVE_FUNCTION_GRAPH_TRACER
> + select HAVE_FUNCTION_GRAPH_TRACER if !SHADOW_CALL_STACK
> select HAVE_GCC_PLUGINS
> select HAVE_HW_BREAKPOINT if PERF_EVENTS
> select HAVE_IRQ_TIME_ACCOUNTING
> --
> 2.24.0.rc0.303.g954a862665-goog
>

--
Kees Cook