Re: [PATCH v7 04/11] scs: disable when function graph tracing is enabled

Kees Cook
2020-01-28T22:50:19Z

On Tue, Jan 28, 2020 at 10:49:27AM -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 SCS when the graph tracer is
> enabled.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

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

-Kees

> ---
> arch/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 1b16aa9a3fe5..0d746373c52e 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -530,6 +530,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK
>
> config SHADOW_CALL_STACK
> bool "Clang Shadow Call Stack"
> + depends on !FUNCTION_GRAPH_TRACER
> depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> help
> This option enables Clang's Shadow Call Stack, which uses a
> --
> 2.25.0.341.g760bfbb309-goog
>

--
Kees Cook