mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

gup 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().

[[email protected]: fix CONFIG_MMU=n build]
  Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com

Signed-off-by: Barry Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: "Matthew Wilcox (Oracle)" <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Naresh Kamboju <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 22 insertions, 15 deletions

diff --git a/mm/gup.c b/mm/gup.c
index e869c634cc9a..32d0e3ca7fbb 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1747,6 +1747,25 @@ static __always_inline long __gup_longterm_locked(struct mm_struct *mm,
 }
 #endif /* CONFIG_FS_DAX || CONFIG_CMA */
 
+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;
+}
+
 #ifdef CONFIG_MMU
 static long __get_user_pages_remote(struct mm_struct *mm,
 				    unsigned long start, unsigned long nr_pages,
@@ -1842,11 +1861,7 @@ 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,
@@ -1892,11 +1907,7 @@ 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,
@@ -2786,11 +2797,7 @@ 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;
 
 	/*