Re: [PATCH v6 4/9] futex: Create get_robust_list2() syscall

[kernel test robot <lkp@intel.com>]

Hi André,

kernel test robot noticed the following build warnings:

[auto build test WARNING on c42ba5a87bdccbca11403b7ca8bad1a57b833732]

url:    https://github.com/intel-lab-lkp/linux/commits/Andr-Almeida/futex-Use-explicit-sizes-for-compat_robust_list-structs/20251122-135406
base:   c42ba5a87bdccbca11403b7ca8bad1a57b833732
patch link:    https://lore.kernel.org/r/20251122-tonyk-robust_futex-v6-4-05fea005a0fd%40igalia.com
patch subject: [PATCH v6 4/9] futex: Create get_robust_list2() syscall
config: i386-randconfig-063-20251123 (https://download.01.org/0day-ci/archive/20251123/202511231423.O6KdcL8r-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251123/202511231423.O6KdcL8r-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511231423.O6KdcL8r-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> kernel/futex/syscalls.c:200:22: sparse: sparse: incorrect type in assignment (different address spaces) @@     expected struct robust_list_head *head @@     got struct robust_list_head [noderef] __user * @@
   kernel/futex/syscalls.c:200:22: sparse:     expected struct robust_list_head *head
   kernel/futex/syscalls.c:200:22: sparse:     got struct robust_list_head [noderef] __user *
>> kernel/futex/syscalls.c:202:24: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected void [noderef] __user *__x @@     got struct robust_list_head *head @@
   kernel/futex/syscalls.c:202:24: sparse:     expected void [noderef] __user *__x
   kernel/futex/syscalls.c:202:24: sparse:     got struct robust_list_head *head

vim +200 kernel/futex/syscalls.c

   160	
   161	SYSCALL_DEFINE4(get_robust_list2, int, pid,
   162			void __user * __user *, head_ptr,
   163			unsigned int, index, unsigned int, flags)
   164	{
   165		void __user *entry_ptr;
   166		uintptr_t entry;
   167	
   168		if (index >= FUTEX_ROBUST_LISTS_PER_USER)
   169			return -EINVAL;
   170	
   171		if (flags)
   172			return -EINVAL;
   173	
   174		/*
   175		 * The first two indexes are reserved for the kernel to be used with the
   176		 * legacy syscall, so we hide them from userspace.
   177		 *
   178		 * We map [0, FUTEX_ROBUST_LISTS_PER_USER) to
   179		 *  [FUTEX_ROBUST_LIST2_IDX, FUTEX_ROBUST_LIST2_MAX_IDX)
   180		 */
   181		index += FUTEX_ROBUST_LIST2_IDX;
   182	
   183		entry_ptr = futex_get_robust_list_common(pid, false, index);
   184		if (IS_ERR(entry_ptr))
   185			return PTR_ERR(entry_ptr);
   186	
   187		entry = (uintptr_t) entry_ptr;
   188	
   189		if (entry & FUTEX_ROBUST_LIST_ENTRY_32BIT) {
   190			entry &= FUTEX_ROBUST_LIST_ENTRY_MASK;
   191	
   192			if (copy_to_user(head_ptr, &entry, sizeof(u32)))
   193				return -EFAULT;
   194	
   195			return 0;
   196		} else {
   197			struct robust_list_head *head;
   198	
   199			entry &= FUTEX_ROBUST_LIST_ENTRY_MASK;
 > 200			head = (__force struct robust_list_head __user *)entry;
   201	
 > 202			return put_user(head, head_ptr);
   203		}
   204	}
   205	

-- 
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