Re: [PATCH v6 08/15] arm64: disable function graph tracing with SCS

Will Deacon
2020-01-16T18:23:26Z

On Fri, Dec 06, 2019 at 02:13:44PM -0800, Sami Tolvanen wrote:
> The graph tracer hooks returns by modifying frame records on the
> (regular) stack, but with SCS the return address is taken from the
> shadow stack, and the value in the frame record has no effect. As we
> don't currently have a mechanism to determine the corresponding slot
> on the shadow stack (and to pass this through the ftrace
> infrastructure), for now let's disable the graph tracer when SCS is
> enabled.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> ---
> arch/arm64/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b1b4476ddb83..49e5f94ff4af 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -149,7 +149,7 @@ 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

I think this is the wrong way around, as we support the graph tracer
today and so I think SHADOW_CALL_STACK should depend on !GRAPH_TRACER
and possibly even EXPERT until this is resolved.

Will