Re: [PATCH 1/1] hugetlbfs: fix bug in pgoff overflow checking

[kbuild test robot]

Hi Mike,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.16-rc7 next-20180329]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Mike-Kravetz/hugetlbfs-fix-bug-in-pgoff-overflow-checking/20180329-231724
config: i386-randconfig-x000-201812 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   fs/hugetlbfs/inode.c: In function 'hugetlbfs_file_mmap':
>> fs/hugetlbfs/inode.c:119:35: warning: left shift count >= width of type [-Wshift-count-overflow]
     (((1UL << (PAGE_SHIFT + 1)) - 1) << \
                                      ^
   fs/hugetlbfs/inode.c:144:38: note: in expansion of macro 'PGOFF_LOFFT_MAX'
     if ((loff_t)vma->vm_pgoff & (loff_t)PGOFF_LOFFT_MAX)
                                         ^~~~~~~~~~~~~~~

vim +119 fs/hugetlbfs/inode.c

   110	
   111	/*
   112	 * Mask used when checking the page offset value passed in via system
   113	 * calls.  This value will be converted to a loff_t which is signed.
   114	 * Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the
   115	 * value.  The extra bit (- 1 in the shift value) is to take the sign
   116	 * bit into account.
   117	 */
   118	#define PGOFF_LOFFT_MAX \
 > 119		(((1UL << (PAGE_SHIFT + 1)) - 1) << \
   120		 ((sizeof(loff_t) * BITS_PER_BYTE) - (PAGE_SHIFT + 1)))
   121	

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