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

Will Deacon will at kernel.org
Thu Jan 16 09:39:51 PST 2020


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 at google.com>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> Reviewed-by: Mark Rutland <mark.rutland at 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



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