powerpc/64/kuap: Move kuap checks out of MSR[RI]=0 regions of exit code

Any kind of WARN causes a program check that will crash with
unrecoverable exception if it occurs when RI is clear.

Fixes: 68b34588 ("powerpc/64/sycall: Implement syscall entry/exit logic in C")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200429065654.1677541-2-npiggin@gmail.com

arch/powerpc/kernel/syscall_64.c

@@ -35,6 +35,8 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	BUG_ON(!FULL_REGS(regs));
 	BUG_ON(regs->softe != IRQS_ENABLED);
 
+	kuap_check_amr();
+
 	account_cpu_user_entry();
 
 #ifdef CONFIG_PPC_SPLPAR
@@ -47,8 +49,6 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	}
 #endif
 
-	kuap_check_amr();
-
 	/*
 	 * This is not required for the syscall exit path, but makes the
 	 * stack frame look nicer. If this was initialised in the first stack
@@ -117,6 +117,8 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 	unsigned long ti_flags;
 	unsigned long ret = 0;
 
+	kuap_check_amr();
+
 	regs->result = r3;
 
 	/* Check whether the syscall is issued inside a restartable sequence */
@@ -204,8 +206,6 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 	local_paca->tm_scratch = regs->msr;
 #endif
 
-	kuap_check_amr();
-
 	account_cpu_user_exit();
 
 	return ret;
@@ -228,6 +228,8 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
 	BUG_ON(!FULL_REGS(regs));
 	BUG_ON(regs->softe != IRQS_ENABLED);
 
+	kuap_check_amr();
+
 	local_irq_save(flags);
 
 again:
@@ -292,8 +294,6 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned
 	local_paca->tm_scratch = regs->msr;
 #endif
 
-	kuap_check_amr();
-
 	account_cpu_user_exit();
 
 	return ret;
@@ -313,6 +313,8 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
 	BUG_ON(regs->msr & MSR_PR);
 	BUG_ON(!FULL_REGS(regs));
 
+	kuap_check_amr();
+
 	if (unlikely(*ti_flagsp & _TIF_EMULATE_STACK_STORE)) {
 		clear_bits(_TIF_EMULATE_STACK_STORE, ti_flagsp);
 		ret = 1;