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

[Nathan Lynch via B4 Relay <devnull+nathanl.linux.ibm.com@kernel.org>]

From: Nathan Lynch <nathanl@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@linux.ibm.com>
---
 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);

-- 
2.39.1