gug prohibits users from calling get_user_pages() with FOLL_PIN. But it
allows users to call get_user_pages() with FOLL_LONGTERM only. It seems
insensible.
since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit
users from calling get_user_pages() with FOLL_LONGTERM while not with
FOLL_PIN.
mm/gup_benchmark.c used to be the only user who did this improperly.
But it has been fixed by moving to use pin_user_pages().
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
---
mm/gup.c | 37 ++++++++++++++++++++++---------------
1 file changed, 22 insertions(+), 15 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index ae096ea7583f..4da669f79566 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1789,6 +1789,25 @@ static long __get_user_pages_remote(struct mm_struct *mm,
gup_flags | FOLL_TOUCH | FOLL_REMOTE);
}
+static bool is_valid_gup_flags(unsigned int gup_flags)
+{
+ /*
+ * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
+ * never directly by the caller, so enforce that with an assertion:
+ */
+ if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+ return false;
+ /*
+ * FOLL_PIN is a prerequisite to FOLL_LONGTERM. Another way of saying
+ * that is, FOLL_LONGTERM is a specific case, more restrictive case of
+ * FOLL_PIN.
+ */
+ if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
+ return false;
+
+ return true;
+}
+
/**
* get_user_pages_remote() - pin user pages in memory
* @mm: mm_struct of target mm
@@ -1854,11 +1873,7 @@ long get_user_pages_remote(struct mm_struct *mm,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *locked)
{
- /*
- * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
- * never directly by the caller, so enforce that with an assertion:
- */
- if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+ if (!is_valid_gup_flags(gup_flags))
return -EINVAL;
return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
@@ -1904,11 +1919,7 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas)
{
- /*
- * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
- * never directly by the caller, so enforce that with an assertion:
- */
- if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+ if (!is_valid_gup_flags(gup_flags))
return -EINVAL;
return __gup_longterm_locked(current->mm, start, nr_pages,
@@ -2810,11 +2821,7 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages)
{
- /*
- * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
- * never directly by the caller, so enforce that:
- */
- if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+ if (!is_valid_gup_flags(gup_flags))
return -EINVAL;
/*
--
2.27.0
