[PATCH 5.14 840/849] powerpc/64s/interrupt: Fix check_return_regs_valid() false positive

[Greg Kroah-Hartman]

From: Nicholas Piggin <npiggin@xxxxxxxxx>

commit 4a5cb51f3db4be547225a4bce7a43d41b231382b upstream.

The check_return_regs_valid() can cause a false positive if the return
regs are marked as norestart and they are an HSRR type interrupt,
because the low bit in the bottom of regs->trap causes interrupt type
matching to fail.

This can occcur for example on bare metal with a HV privileged doorbell
interrupt that causes a signal, but do_signal returns early because
get_signal() fails, and takes the "No signal to deliver" path. In this
case no signal was delivered so the return location is not changed so
return SRRs are not invalidated, yet set_trap_norestart is called, which
messes up the match. Building go-1.16.6 is known to reproduce this.

Fix it by using the TRAP() accessor which masks out the low bit.

Fixes: 6eaaf9de3599 ("powerpc/64s/interrupt: Check and fix srr_valid without crashing")
Cc: stable@xxxxxxxxxxxxxxx # v5.14+
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20211026122531.3599918-1-npiggin@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/kernel/interrupt.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -268,7 +268,7 @@ static void check_return_regs_valid(stru
 	if (trap_is_scv(regs))
 		return;
 
-	trap = regs->trap;
+	trap = TRAP(regs);
 	// EE in HV mode sets HSRRs like 0xea0
 	if (cpu_has_feature(CPU_FTR_HVMODE) && trap == INTERRUPT_EXTERNAL)
 		trap = 0xea0;