[PATCH 08/10] mm: replace __access_remote_vm() write parameter with gup_flags

Lorenzo Stoakes
2016-10-13T00:20:18Z

This patch removes the write parameter from __access_remote_vm() and replaces it
with a gup_flags parameter as use of this function previously _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>
---
mm/memory.c | 23 +++++++++++++++--------
mm/nommu.c | 9 ++++++---
2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 20a9adb..79ebed3 100644
--- a/mm/memory.c
+++ b/mm/memory.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;
diff --git a/mm/nommu.c b/mm/nommu.c
index 70cb844..bde7df3 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -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;
--
2.10.0