[4.2.y-ckt stable] Patch "s390/mm: four page table levels vs. fork" has been added to the 4.2.y-ckt tree
Kamal Mostafa
kamal at canonical.com
Tue Mar 15 16:04:07 UTC 2016
This is a note to let you know that I have just added a patch titled
s390/mm: four page table levels vs. fork
to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree
which can be found at:
http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue
This patch is scheduled to be released in version 4.2.8-ckt6.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From 5b62f74b65718adeccbb5e69e3b3750cf6f1e281 Mon Sep 17 00:00:00 2001
From: Martin Schwidefsky <schwidefsky at de.ibm.com>
Date: Mon, 15 Feb 2016 14:46:49 +0100
Subject: s390/mm: four page table levels vs. fork
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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commit 3446c13b268af86391d06611327006b059b8bab1 upstream.
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 KoĆcielnicki <koriakin at 0x04.net>
Reviewed-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
arch/s390/include/asm/mmu_context.h | 16 +++++++++++-----
arch/s390/include/asm/pgalloc.h | 24 +++++++++++++++++++-----
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 fb1b93e..e485817 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 7b7858f..d7cc79f 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)
--
2.7.0
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