powerpc/32s: Create C version of kuap save/restore/check helpers

In preparation of porting PPC32 to C syscall entry/exit,
create C version of kuap_save_and_lock() and kuap_user_restore() and
kuap_kernel_restore() and kuap_assert_locked() and
kuap_get_and_assert_locked() on book3s/32.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2be8fb729da4a0f9863b25e1b9d547174fcd5056.1615552867.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/book3s/32/kup.h

@@ -72,6 +72,51 @@ static inline void kuap_update_sr(u32 sr, u32 addr, u32 end)
 	isync();	/* Context sync required after mtsr() */
 }
 
+static inline void kuap_save_and_lock(struct pt_regs *regs)
+{
+	unsigned long kuap = current->thread.kuap;
+	u32 addr = kuap & 0xf0000000;
+	u32 end = kuap << 28;
+
+	regs->kuap = kuap;
+	if (unlikely(!kuap))
+		return;
+
+	current->thread.kuap = 0;
+	kuap_update_sr(mfsr(addr) | SR_KS, addr, end);	/* Set Ks */
+}
+
+static inline void kuap_user_restore(struct pt_regs *regs)
+{
+}
+
+static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap)
+{
+	u32 addr = regs->kuap & 0xf0000000;
+	u32 end = regs->kuap << 28;
+
+	current->thread.kuap = regs->kuap;
+
+	if (unlikely(regs->kuap == kuap))
+		return;
+
+	kuap_update_sr(mfsr(addr) & ~SR_KS, addr, end);	/* Clear Ks */
+}
+
+static inline unsigned long kuap_get_and_assert_locked(void)
+{
+	unsigned long kuap = current->thread.kuap;
+
+	WARN_ON_ONCE(IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && kuap != 0);
+
+	return kuap;
+}
+
+static inline void kuap_assert_locked(void)
+{
+	kuap_get_and_assert_locked();
+}
+
 static __always_inline void allow_user_access(void __user *to, const void __user *from,
 					      u32 size, unsigned long dir)
 {