From b4d70a6134d2152d692ccc873ff6fa3351631927 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Mon, 7 Dec 2020 20:56:38 +0100 Subject: s390/mm: use invalid asce for user space when switching to init_mm Currently only idle_task_exit() explicitly switches (switch_mm) to init_mm. This causes the kernel asce to be loaded into cr7 and therefore it would be used for potential user space accesses. This is currently no problem since idle_task_exit() is nearly the last thing a CPU executes before it is taken down. However things might change - and therefore make sure that always the invalid asce is used for cr7 when active_mm is init_mm. This makes sure that all potential user space accesses will fail, instead of accessing kernel address space. Reviewed-by: Alexander Gordeev Signed-off-by: Heiko Carstens --- arch/s390/include/asm/mmu_context.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h index 87a84fc59fc3..5dc49c467319 100644 --- a/arch/s390/include/asm/mmu_context.h +++ b/arch/s390/include/asm/mmu_context.h @@ -76,7 +76,10 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, { int cpu = smp_processor_id(); - S390_lowcore.user_asce = next->context.asce; + if (next == &init_mm) + S390_lowcore.user_asce = s390_invalid_asce; + else + S390_lowcore.user_asce = next->context.asce; cpumask_set_cpu(cpu, &next->context.cpu_attach_mask); /* Clear previous user-ASCE from CR7 */ __ctl_load(s390_invalid_asce, 7, 7); -- cgit v1.2.3