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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2016-02-15 14:46:49 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2016-03-10 09:21:24 +0100
commit3446c13b268af86391d06611327006b059b8bab1 (patch)
treed321bf624bb2e937e806dd565c6de3d3a8d83e36
parent7a76aa95f6f6682db5629449d763251d1c9f8c4e (diff)
downloadlinux-sh-3446c13b268af86391d06611327006b059b8bab1.tar.gz
s390/mm: four page table levels vs. fork
The fork of a process with four page table levels is broken since git commit 6252d702c5311ce9 "[S390] dynamic page tables." All new mm contexts are created with three page table levels and an asce limit of 4TB. If the parent has four levels dup_mmap will add vmas to the new context which are outside of the asce limit. The subsequent call to copy_page_range will walk the three level page table structure of the new process with non-zero pgd and pud indexes. This leads to memory clobbers as the pgd_index *and* the pud_index is added to the mm->pgd pointer without a pgd_deref in between. The init_new_context() function is selecting the number of page table levels for a new context. The function is used by mm_init() which in turn is called by dup_mm() and mm_alloc(). These two are used by fork() and exec(). The init_new_context() function can distinguish the two cases by looking at mm->context.asce_limit, for fork() the mm struct has been copied and the number of page table levels may not change. For exec() the mm_alloc() function set the new mm structure to zero, in this case a three-level page table is created as the temporary stack space is located at STACK_TOP_MAX = 4TB. This fixes CVE-2016-2143. Reported-by: Marcin Koƛcielnicki <koriakin@0x04.net> Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: stable@vger.kernel.org Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
-rw-r--r--arch/s390/include/asm/mmu_context.h16
-rw-r--r--arch/s390/include/asm/pgalloc.h24
2 files changed, 30 insertions, 10 deletions
diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index fb1b93ea3e3f..e485817f7b1a 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -15,17 +15,25 @@
static inline int init_new_context(struct task_struct *tsk,
struct mm_struct *mm)
{
+ spin_lock_init(&mm->context.list_lock);
+ INIT_LIST_HEAD(&mm->context.pgtable_list);
+ INIT_LIST_HEAD(&mm->context.gmap_list);
cpumask_clear(&mm->context.cpu_attach_mask);
atomic_set(&mm->context.attach_count, 0);
mm->context.flush_mm = 0;
- mm->context.asce_bits = _ASCE_TABLE_LENGTH | _ASCE_USER_BITS;
- mm->context.asce_bits |= _ASCE_TYPE_REGION3;
#ifdef CONFIG_PGSTE
mm->context.alloc_pgste = page_table_allocate_pgste;
mm->context.has_pgste = 0;
mm->context.use_skey = 0;
#endif
- mm->context.asce_limit = STACK_TOP_MAX;
+ if (mm->context.asce_limit == 0) {
+ /* context created by exec, set asce limit to 4TB */
+ mm->context.asce_bits = _ASCE_TABLE_LENGTH |
+ _ASCE_USER_BITS | _ASCE_TYPE_REGION3;
+ mm->context.asce_limit = STACK_TOP_MAX;
+ } else if (mm->context.asce_limit == (1UL << 31)) {
+ mm_inc_nr_pmds(mm);
+ }
crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));
return 0;
}
@@ -111,8 +119,6 @@ static inline void activate_mm(struct mm_struct *prev,
static inline void arch_dup_mmap(struct mm_struct *oldmm,
struct mm_struct *mm)
{
- if (oldmm->context.asce_limit < mm->context.asce_limit)
- crst_table_downgrade(mm, oldmm->context.asce_limit);
}
static inline void arch_exit_mmap(struct mm_struct *mm)
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h
index 7b7858f158b4..d7cc79fb6191 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -100,12 +100,26 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
static inline pgd_t *pgd_alloc(struct mm_struct *mm)
{
- spin_lock_init(&mm->context.list_lock);
- INIT_LIST_HEAD(&mm->context.pgtable_list);
- INIT_LIST_HEAD(&mm->context.gmap_list);
- return (pgd_t *) crst_table_alloc(mm);
+ unsigned long *table = crst_table_alloc(mm);
+
+ if (!table)
+ return NULL;
+ if (mm->context.asce_limit == (1UL << 31)) {
+ /* Forking a compat process with 2 page table levels */
+ if (!pgtable_pmd_page_ctor(virt_to_page(table))) {
+ crst_table_free(mm, table);
+ return NULL;
+ }
+ }
+ return (pgd_t *) table;
+}
+
+static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
+{
+ if (mm->context.asce_limit == (1UL << 31))
+ pgtable_pmd_page_dtor(virt_to_page(pgd));
+ crst_table_free(mm, (unsigned long *) pgd);
}
-#define pgd_free(mm, pgd) crst_table_free(mm, (unsigned long *) pgd)
static inline void pmd_populate(struct mm_struct *mm,
pmd_t *pmd, pgtable_t pte)