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mm: replace __access_remote_vm() write parameter with gup_flags

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>
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lorenzo-stoakes authored and torvalds committed Oct 13, 2016
1 parent 9beae1e commit 442486ec1096781c50227b73f721a63974b0fdda
Showing with 21 additions and 11 deletions.
  1. +15 −8 mm/memory.c
  2. +6 −3 mm/nommu.c
@@ -3869,14 +3869,11 @@ 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 */
@@ -3886,7 +3883,7 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
struct page *page = NULL;
ret = get_user_pages_remote(tsk, mm, addr, 1,
flags, &page, &vma);
gup_flags, &page, &vma);
if (ret <= 0) {
#ifndef CONFIG_HAVE_IOREMAP_PROT
break;
@@ -3945,7 +3942,12 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
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);
}
/*
@@ -3958,12 +3960,17 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr,
{
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;
@@ -1809,9 +1809,10 @@ void filemap_map_pages(struct fault_env *fe,
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);
@@ -1853,7 +1854,8 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
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);
}
/*
@@ -1871,7 +1873,8 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
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;

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