Re: [PATCH v4 11/17] arm64: disable function graph tracing with SCS

Mark Rutland
2019-11-04T17:11:57Z

On Fri, Nov 01, 2019 at 03:11:44PM -0700, Sami Tolvanen 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.

Can you please elaborate on _how_ this is incompatible in the commit
message?

For example, it's not clear to me if you mean that's functionally
incompatible, or if you're trying to remove return-altering gadgets.

If there's a functional incompatibility, please spell that out a bit
more clearly. Likewise if this is about minimizing the set of places
that can mess with control-flow outside of usual function conventions.

Thanks,
Mark.

>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
> 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.rc1.363.gb1bccd3e3d-goog
>