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().

[akpm@linux-foundation.org: fix CONFIG_MMU=n build]
Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@mail.gmail.com
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@hisilicon.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index e869c63..32d0e3c 100644 (file)
--- 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;
 
        /*