[PATCH 4.4 80/88] mm: replace __access_remote_vm() write parameter with gup_flags

Greg Kroah-Hartman
2018-12-14T12:17:03Z

From: Lorenzo Stoakes <lstoakes@gmail.com>

commit 442486ec1096781c50227b73f721a63974b0fdda upstream.

This removes the 'write' argument from __access_remote_vm() and replaces
it with 'gup_flags' as use of this function previously silently implied
FOLL_FORCE, whereas after this patch callers explicitly pass this flag.

We make this explicit as use of FOLL_FORCE can result in surprising
behaviour (and hence bugs) within the mm subsystem.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 4.4: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/memory.c | 23 +++++++++++++++--------
mm/nommu.c | 9 ++++++---
2 files changed, 21 insertions(+), 11 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3711,14 +3711,11 @@ EXPORT_SYMBOL_GPL(generic_access_phys);
* given task for page fault accounting.
*/
static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
- unsigned long addr, void *buf, int len, int write)
+ unsigned long addr, void *buf, int len, unsigned int gup_flags)
{
struct vm_area_struct *vma;
void *old_buf = buf;
- unsigned int flags = FOLL_FORCE;
-
- if (write)
- flags |= FOLL_WRITE;
+ int write = gup_flags & FOLL_WRITE;

down_read(&mm->mmap_sem);
/* ignore errors, just check how much was successfully transferred */
@@ -3728,7 +3725,7 @@ static int __access_remote_vm(struct tas
struct page *page = NULL;

ret = get_user_pages(tsk, mm, addr, 1,
- flags, &page, &vma);
+ gup_flags, &page, &vma);
if (ret <= 0) {
#ifndef CONFIG_HAVE_IOREMAP_PROT
break;
@@ -3787,7 +3784,12 @@ static int __access_remote_vm(struct tas
int access_remote_vm(struct mm_struct *mm, unsigned long addr,
void *buf, int len, int write)
{
- return __access_remote_vm(NULL, mm, addr, buf, len, write);
+ unsigned int flags = FOLL_FORCE;
+
+ if (write)
+ flags |= FOLL_WRITE;
+
+ return __access_remote_vm(NULL, mm, addr, buf, len, flags);
}

/*
@@ -3800,12 +3802,17 @@ int access_process_vm(struct task_struct
{
struct mm_struct *mm;
int ret;
+ unsigned int flags = FOLL_FORCE;

mm = get_task_mm(tsk);
if (!mm)
return 0;

- ret = __access_remote_vm(tsk, mm, addr, buf, len, write);
+ if (write)
+ flags |= FOLL_WRITE;
+
+ ret = __access_remote_vm(tsk, mm, addr, buf, len, flags);
+
mmput(mm);

return ret;
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1929,9 +1929,10 @@ void filemap_map_pages(struct vm_area_st
EXPORT_SYMBOL(filemap_map_pages);

static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
- unsigned long addr, void *buf, int len, int write)
+ unsigned long addr, void *buf, int len, unsigned int gup_flags)
{
struct vm_area_struct *vma;
+ int write = gup_flags & FOLL_WRITE;

down_read(&mm->mmap_sem);

@@ -1973,7 +1974,8 @@ static int __access_remote_vm(struct tas
int access_remote_vm(struct mm_struct *mm, unsigned long addr,
void *buf, int len, int write)
{
- return __access_remote_vm(NULL, mm, addr, buf, len, write);
+ return __access_remote_vm(NULL, mm, addr, buf, len,
+ write ? FOLL_WRITE : 0);
}

/*
@@ -1991,7 +1993,8 @@ int access_process_vm(struct task_struct
if (!mm)
return 0;

- len = __access_remote_vm(tsk, mm, addr, buf, len, write);
+ len = __access_remote_vm(tsk, mm, addr, buf, len,
+ write ? FOLL_WRITE : 0);

mmput(mm);
return len;