path: root/arch/s390
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authorHeiko Carstens <hca@linux.ibm.com>2020-12-07 20:56:38 +0100
committerHeiko Carstens <hca@linux.ibm.com>2020-12-09 21:02:08 +0100
commitb4d70a6134d2152d692ccc873ff6fa3351631927 (patch)
tree506d435fedb08619cb849906cb4e207139c6b337 /arch/s390
parent454efcf82ea17d7efeb86ebaa20775a21ec87d27 (diff)
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 <agordeev@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Diffstat (limited to 'arch/s390')
1 files changed, 4 insertions, 1 deletions
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);

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