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authorLinus Torvalds <torvalds@linux-foundation.org>2020-04-28 09:13:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-28 09:13:08 -0700
commit3f777e19d171670ab558a6d5e6b1ac7f9b6c574f (patch)
tree2fa61424cd8288aa8711b1ed742eb27926a0501e /arch
parent51184ae37e0518fd90cb437a2fbc953ae558cd0d (diff)
parent316ec154810960052d4586b634156c54d0778f74 (diff)
Merge tag 'cve-2020-11884' from emailed bundle
Pull s390 fix from Christian Borntraeger: "Fix a race between page table upgrade and uaccess on s390. This fixes CVE-2020-11884 which allows for a local kernel crash or code execution" * tag 'cve-2020-11884' from emailed bundle: s390/mm: fix page table upgrade vs 2ndary address mode accesses
Diffstat (limited to 'arch')
-rw-r--r--arch/s390/lib/uaccess.c4
-rw-r--r--arch/s390/mm/pgalloc.c16
2 files changed, 18 insertions, 2 deletions
diff --git a/arch/s390/lib/uaccess.c b/arch/s390/lib/uaccess.c
index c4f8039a35e8..0267405ab7c6 100644
--- a/arch/s390/lib/uaccess.c
+++ b/arch/s390/lib/uaccess.c
@@ -64,10 +64,13 @@ mm_segment_t enable_sacf_uaccess(void)
{
mm_segment_t old_fs;
unsigned long asce, cr;
+ unsigned long flags;
old_fs = current->thread.mm_segment;
if (old_fs & 1)
return old_fs;
+ /* protect against a concurrent page table upgrade */
+ local_irq_save(flags);
current->thread.mm_segment |= 1;
asce = S390_lowcore.kernel_asce;
if (likely(old_fs == USER_DS)) {
@@ -83,6 +86,7 @@ mm_segment_t enable_sacf_uaccess(void)
__ctl_load(asce, 7, 7);
set_cpu_flag(CIF_ASCE_SECONDARY);
}
+ local_irq_restore(flags);
return old_fs;
}
EXPORT_SYMBOL(enable_sacf_uaccess);
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 498c98a312f4..fff169d64711 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -70,8 +70,20 @@ static void __crst_table_upgrade(void *arg)
{
struct mm_struct *mm = arg;
- if (current->active_mm == mm)
- set_user_asce(mm);
+ /* we must change all active ASCEs to avoid the creation of new TLBs */
+ if (current->active_mm == mm) {
+ S390_lowcore.user_asce = mm->context.asce;
+ if (current->thread.mm_segment == USER_DS) {
+ __ctl_load(S390_lowcore.user_asce, 1, 1);
+ /* Mark user-ASCE present in CR1 */
+ clear_cpu_flag(CIF_ASCE_PRIMARY);
+ }
+ if (current->thread.mm_segment == USER_DS_SACF) {
+ __ctl_load(S390_lowcore.user_asce, 7, 7);
+ /* enable_sacf_uaccess does all or nothing */
+ WARN_ON(!test_cpu_flag(CIF_ASCE_SECONDARY));
+ }
+ }
__tlb_flush_local();
}