[PATCH 7/8] powerpc/rtas: warn on unsafe argument to rtas_call_unlocked()

[Andrew Donnellan]

On Mon, 2023-03-06 at 15:33 -0600, Nathan Lynch via B4 Relay wrote:
> From: Nathan Lynch <nathanl at linux.ibm.com>
> 
> Any caller of rtas_call_unlocked() must provide an rtas_args
> parameter
> block distinct from the core rtas_args buffer used by the rtas_call()
> path. It's an unlikely error to make, but the potential consequences
> are grim, and it's trivial to check.
> 
> Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>

call_rtas_display_status() seems to do exactly this, or am I missing
something?

> ---
>  arch/powerpc/kernel/rtas.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 633c925164e7..47a2aa43d7d4 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -1042,6 +1042,13 @@ void rtas_call_unlocked(struct rtas_args
> *args, int token, int nargs, int nret,
>  {
>         va_list list;
>  
> +       /*
> +        * Callers must not use rtas_args; otherwise they risk
> +        * corrupting the state of the rtas_call() path, which is
> +        * serialized by rtas_lock.
> +        */
> +       WARN_ON(args == &rtas_args);
> +
>         va_start(list, nret);
>         va_rtas_call(args, token, nargs, nret, list);
>         va_end(list);
> 

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd at linux.ibm.com   IBM Australia Limited