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SubjectRe: [PATCH] ftrace: Allow WITH_ARGS flavour of graph tracer with shadow call stack
On Fri,  9 Dec 2022 15:34:02 +0100
Ard Biesheuvel <ardb@kernel.org> wrote:

> The recent switch on arm64 from DYNAMIC_FTRACE_WITH_REGS to
> DYNAMIC_FTRACE_WITH_ARGS failed to take into account that we currently
> require the former in order to allow the function graph tracer to be
> enabled in combination with shadow call stacks. This means that this is
> no longer permitted at all, in spite of the fact that either flavour of
> ftrace works perfectly fine in this combination.
>
> Given that arm64 is the only arch that implements shadow call stacks in
> the first place, let's update the condition to just reflect the arm64
> change. When other architectures adopt shadow call stack support, this
> can be revisited if needed.

This brings a question. Is the SCS safe if kretprobe(rethook) is enabled?
it also changes the stack entry after a calling function.

Thank you,

>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> arch/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 072a1b39e3afd0d1..683f365b5e31c856 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -635,7 +635,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK
> config SHADOW_CALL_STACK
> bool "Shadow Call Stack"
> depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> - depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
> + depends on DYNAMIC_FTRACE_WITH_ARGS || !FUNCTION_GRAPH_TRACER
> help
> This option enables the compiler's Shadow Call Stack, which
> uses a shadow stack to protect function return addresses from
> --
> 2.35.1
>


--
Masami Hiramatsu (Google) <mhiramat@kernel.org>

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