[PATCH 07/10] mm: replace get_user_pages_remote() write/force parameters with gup_flags

Lorenzo Stoakes
2016-10-13T00:20:17Z

This patch removes the write and force parameters from get_user_pages_remote()
and replaces them with a gup_flags parameter to make the use of FOLL_FORCE
explicit in callers as use of this flag can result in surprising behaviour (and
hence bugs) within the mm subsystem.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
drivers/gpu/drm/etnaviv/etnaviv_gem.c | 7 +++++--
drivers/gpu/drm/i915/i915_gem_userptr.c | 6 +++++-
drivers/infiniband/core/umem_odp.c | 7 +++++--
fs/exec.c | 9 +++++++--
include/linux/mm.h | 2 +-
kernel/events/uprobes.c | 6 ++++--
mm/gup.c | 22 +++++++---------------
mm/memory.c | 6 +++++-
security/tomoyo/domain.c | 2 +-
9 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index 5ce3603..0370b84 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -748,19 +748,22 @@ static struct page **etnaviv_gem_userptr_do_get_pages(
int ret = 0, pinned, npages = etnaviv_obj->base.size >> PAGE_SHIFT;
struct page **pvec;
uintptr_t ptr;
+ unsigned int flags = 0;

pvec = drm_malloc_ab(npages, sizeof(struct page *));
if (!pvec)
return ERR_PTR(-ENOMEM);

+ if (!etnaviv_obj->userptr.ro)
+ flags |= FOLL_WRITE;
+
pinned = 0;
ptr = etnaviv_obj->userptr.ptr;

down_read(&mm->mmap_sem);
while (pinned < npages) {
ret = get_user_pages_remote(task, mm, ptr, npages - pinned,
- !etnaviv_obj->userptr.ro, 0,
- pvec + pinned, NULL);
+ flags, pvec + pinned, NULL);
if (ret < 0)
break;

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index e537930..c6f780f 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -508,6 +508,10 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
pvec = drm_malloc_gfp(npages, sizeof(struct page *), GFP_TEMPORARY);
if (pvec != NULL) {
struct mm_struct *mm = obj->userptr.mm->mm;
+ unsigned int flags = 0;
+
+ if (!obj->userptr.read_only)
+ flags |= FOLL_WRITE;

ret = -EFAULT;
if (atomic_inc_not_zero(&mm->mm_users)) {
@@ -517,7 +521,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
(work->task, mm,
obj->userptr.ptr + pinned * PAGE_SIZE,
npages - pinned,
- !obj->userptr.read_only, 0,
+ flags,
pvec + pinned, NULL);
if (ret < 0)
break;
diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index 75077a0..1f0fe32 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -527,6 +527,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
u64 off;
int j, k, ret = 0, start_idx, npages = 0;
u64 base_virt_addr;
+ unsigned int flags = 0;

if (access_mask == 0)
return -EINVAL;
@@ -556,6 +557,9 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
goto out_put_task;
}

+ if (access_mask & ODP_WRITE_ALLOWED_BIT)
+ flags |= FOLL_WRITE;
+
start_idx = (user_virt - ib_umem_start(umem)) >> PAGE_SHIFT;
k = start_idx;

@@ -574,8 +578,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
*/
npages = get_user_pages_remote(owning_process, owning_mm,
user_virt, gup_num_pages,
- access_mask & ODP_WRITE_ALLOWED_BIT,
- 0, local_page_list, NULL);
+ flags, local_page_list, NULL);
up_read(&owning_mm->mmap_sem);

if (npages < 0)
diff --git a/fs/exec.c b/fs/exec.c
index 6fcfb3f..4e497b9 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -191,6 +191,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
{
struct page *page;
int ret;
+ unsigned int gup_flags = FOLL_FORCE;

#ifdef CONFIG_STACK_GROWSUP
if (write) {
@@ -199,12 +200,16 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
return NULL;
}
#endif
+
+ if (write)
+ gup_flags |= FOLL_WRITE;
+
/*
* We are doing an exec(). 'current' is the process
* doing the exec and bprm->mm is the new process's mm.
*/
- ret = get_user_pages_remote(current, bprm->mm, pos, 1, write,
- 1, &page, NULL);
+ ret = get_user_pages_remote(current, bprm->mm, pos, 1, gup_flags,
+ &page, NULL);
if (ret <= 0)
return NULL;

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 686a477..2a481d3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1276,7 +1276,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
struct vm_area_struct **vmas, int *nonblocking);
long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, unsigned long nr_pages,
- int write, int force, struct page **pages,
+ unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas);
long get_user_pages(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index d4129bb..f9ec9ad 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -300,7 +300,8 @@ int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,

retry:
/* Read the page with vaddr into memory */
- ret = get_user_pages_remote(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma);
+ ret = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &old_page,
+ &vma);
if (ret <= 0)
return ret;

@@ -1710,7 +1711,8 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
* but we treat this as a 'remote' access since it is
* essentially a kernel access to the memory.
*/
- result = get_user_pages_remote(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
+ result = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &page,
+ NULL);
if (result < 0)
return result;

diff --git a/mm/gup.c b/mm/gup.c
index dc91303..0deecf3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -905,9 +905,7 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
* @mm: mm_struct of target mm
* @start: starting user address
* @nr_pages: number of pages from start to pin
- * @write: whether pages will be written to by the caller
- * @force: whether to force access even when user mapping is currently
- * protected (but never forces write access to shared mapping).
+ * @gup_flags: flags modifying lookup behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long. Or NULL, if caller
* only intends to ensure the pages are faulted in.
@@ -936,9 +934,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
* or similar operation cannot guarantee anything stronger anyway because
* locks can't be held over the syscall boundary.
*
- * If write=0, the page must not be written to. If the page is written to,
- * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
- * after the page is finished with, and before put_page is called.
+ * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
+ * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
+ * be called after the page is finished with, and before put_page is called.
*
* get_user_pages is typically used for fewer-copy IO operations, to get a
* handle on the memory by some means other than accesses via the user virtual
@@ -955,18 +953,12 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
*/
long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, unsigned long nr_pages,
- int write, int force, struct page **pages,
+ unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas)
{
- unsigned int flags = FOLL_TOUCH | FOLL_REMOTE;
-
- if (write)
- flags |= FOLL_WRITE;
- if (force)
- flags |= FOLL_FORCE;
-
return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
- NULL, false, flags);
+ NULL, false,
+ gup_flags | FOLL_TOUCH | FOLL_REMOTE);
}
EXPORT_SYMBOL(get_user_pages_remote);

diff --git a/mm/memory.c b/mm/memory.c
index fc1987d..20a9adb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3873,6 +3873,10 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
{
struct vm_area_struct *vma;
void *old_buf = buf;
+ unsigned int flags = FOLL_FORCE;
+
+ if (write)
+ flags |= FOLL_WRITE;

down_read(&mm->mmap_sem);
/* ignore errors, just check how much was successfully transferred */
@@ -3882,7 +3886,7 @@ 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,
- write, 1, &page, &vma);
+ flags, &page, &vma);
if (ret <= 0) {
#ifndef CONFIG_HAVE_IOREMAP_PROT
break;
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index ade7c6c..682b73a 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -881,7 +881,7 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
* the execve().
*/
if (get_user_pages_remote(current, bprm->mm, pos, 1,
- 0, 1, &page, NULL) <= 0)
+ FOLL_FORCE, &page, NULL) <= 0)
return false;
#else
page = bprm->page[pos / PAGE_SIZE];
--
2.10.0