From: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxxxxxxxx: fix CONFIG_MMU=n build] Link: https://lkml.kernel.org/r/CA+G9fYuNS3k0DVT62twfV746pfNhCSrk5sVMcOcQ1PGGnEseyw@xxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/20200819110100.23504-1-song.bao.hua@xxxxxxxxxxxxx Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx> 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> Cc: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 37 ++++++++++++++++++++++--------------- 1 file changed, 22 insertions(+), 15 deletions(-) --- a/mm/gup.c~mm-gup-dont-permit-users-to-call-get_user_pages-with-foll_longterm +++ a/mm/gup.c @@ -1747,6 +1747,25 @@ static __always_inline long __gup_longte } #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_str 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 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_on 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; /* _
