From e6ec07dc6dd498415bc8cc49437d5ec9e09cc48e Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Wed, 20 Mar 2024 10:38:58 +0100 Subject: [PATCH] s390/mm: fix NULL pointer dereference The recently added check to figure out if a fault happened on gmap ASCE dereferences the gmap pointer in lowcore without checking that it is not NULL. For all non-KVM processes the pointer is NULL, so that some value from lowcore will be read. With the current layouts of struct gmap and struct lowcore the read value (aka ASCE) is zero, so that this doesn't lead to any observable bug; at least currently. Fix this by adding the missing NULL pointer check. Fixes: 64c3431808bd ("s390/entry: compare gmap asce to determine guest/host fault") Acked-by: Sven Schnelle Reviewed-by: Claudio Imbrenda Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik --- arch/s390/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index c421dd44ffbe0..0c66b32e0f9f1 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -75,7 +75,7 @@ static enum fault_type get_fault_type(struct pt_regs *regs) if (!IS_ENABLED(CONFIG_PGSTE)) return KERNEL_FAULT; gmap = (struct gmap *)S390_lowcore.gmap; - if (regs->cr1 == gmap->asce) + if (gmap && gmap->asce == regs->cr1) return GMAP_FAULT; return KERNEL_FAULT; } -- 2.30.2