95 lines
3.4 KiB
Diff
95 lines
3.4 KiB
Diff
|
From 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 Mon Sep 17 00:00:00 2001
|
||
|
From: Linus Torvalds <torvalds@linux-foundation.org>
|
||
|
Date: Thu, 13 Oct 2016 13:07:36 -0700
|
||
|
Subject: mm: remove gup_flags FOLL_WRITE games from __get_user_pages()
|
||
|
|
||
|
This is an ancient bug that was actually attempted to be fixed once
|
||
|
(badly) by me eleven years ago in commit 4ceb5db9757a ("Fix
|
||
|
get_user_pages() race for write access") but that was then undone due to
|
||
|
problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug").
|
||
|
|
||
|
In the meantime, the s390 situation has long been fixed, and we can now
|
||
|
fix it by checking the pte_dirty() bit properly (and do it better). The
|
||
|
s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement
|
||
|
software dirty bits") which made it into v3.9. Earlier kernels will
|
||
|
have to look at the page state itself.
|
||
|
|
||
|
Also, the VM has become more scalable, and what used a purely
|
||
|
theoretical race back then has become easier to trigger.
|
||
|
|
||
|
To fix it, we introduce a new internal FOLL_COW flag to mark the "yes,
|
||
|
we already did a COW" rather than play racy games with FOLL_WRITE that
|
||
|
is very fundamental, and then use the pte dirty flag to validate that
|
||
|
the FOLL_COW flag is still valid.
|
||
|
|
||
|
Reported-and-tested-by: Phil "not Paul" Oester <kernel@linuxace.com>
|
||
|
Acked-by: Hugh Dickins <hughd@google.com>
|
||
|
Reviewed-by: Michal Hocko <mhocko@suse.com>
|
||
|
Cc: Andy Lutomirski <luto@kernel.org>
|
||
|
Cc: Kees Cook <keescook@chromium.org>
|
||
|
Cc: Oleg Nesterov <oleg@redhat.com>
|
||
|
Cc: Willy Tarreau <w@1wt.eu>
|
||
|
Cc: Nick Piggin <npiggin@gmail.com>
|
||
|
Cc: Greg Thelen <gthelen@google.com>
|
||
|
Cc: stable@vger.kernel.org
|
||
|
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
||
|
---
|
||
|
include/linux/mm.h | 1 +
|
||
|
mm/gup.c | 14 ++++++++++++--
|
||
|
2 files changed, 13 insertions(+), 2 deletions(-)
|
||
|
|
||
|
diff --git a/include/linux/mm.h b/include/linux/mm.h
|
||
|
index e9caec6..ed85879 100644
|
||
|
--- a/include/linux/mm.h
|
||
|
+++ b/include/linux/mm.h
|
||
|
@@ -2232,6 +2232,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
|
||
|
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
|
||
|
#define FOLL_MLOCK 0x1000 /* lock present pages */
|
||
|
#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
|
||
|
+#define FOLL_COW 0x4000 /* internal GUP flag */
|
||
|
|
||
|
typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
|
||
|
void *data);
|
||
|
diff --git a/mm/gup.c b/mm/gup.c
|
||
|
index 96b2b2f..22cc22e 100644
|
||
|
--- a/mm/gup.c
|
||
|
+++ b/mm/gup.c
|
||
|
@@ -60,6 +60,16 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
|
||
|
return -EEXIST;
|
||
|
}
|
||
|
|
||
|
+/*
|
||
|
+ * FOLL_FORCE can write to even unwritable pte's, but only
|
||
|
+ * after we've gone through a COW cycle and they are dirty.
|
||
|
+ */
|
||
|
+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
|
||
|
+{
|
||
|
+ return pte_write(pte) ||
|
||
|
+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
|
||
|
+}
|
||
|
+
|
||
|
static struct page *follow_page_pte(struct vm_area_struct *vma,
|
||
|
unsigned long address, pmd_t *pmd, unsigned int flags)
|
||
|
{
|
||
|
@@ -95,7 +105,7 @@ retry:
|
||
|
}
|
||
|
if ((flags & FOLL_NUMA) && pte_protnone(pte))
|
||
|
goto no_page;
|
||
|
- if ((flags & FOLL_WRITE) && !pte_write(pte)) {
|
||
|
+ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
|
||
|
pte_unmap_unlock(ptep, ptl);
|
||
|
return NULL;
|
||
|
}
|
||
|
@@ -412,7 +422,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
|
||
|
* reCOWed by userspace write).
|
||
|
*/
|
||
|
if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
|
||
|
- *flags &= ~FOLL_WRITE;
|
||
|
+ *flags |= FOLL_COW;
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
--
|
||
|
cgit v0.12
|
||
|
|