Re: [PATCH] x86/resctrl: Prevent possible overrun during bitmap operations

On Wed, Jun 19, 2019 at 01:27:16PM -0700, Reinette Chatre wrote:

@@ -2494,26 +2498,19 @@ static int mkdir_mondata_all(struct kernfs_node *parent_kn, */ static void cbm_ensure_valid(u32 *_val, struct rdt_resource *r) {

• /*

• * Convert the u32 _val to an unsigned long required by all the bit
  

• * operations within this function. No more than 32 bits of this
  

• * converted value can be accessed because all bit operations are
  

• * additionally provided with cbm_len that is initialized during
  

• * hardware enumeration using five bits from the EAX register and
  

• * thus never can exceed 32 bits.
  

• */
  

• unsigned long *val = (unsigned long *)_val;

• unsigned long val = *_val; unsigned int cbm_len = r->cache.cbm_len; unsigned long first_bit, zero_bit;

Please sort function local variables declaration in a reverse christmas tree order:

<type A> longest_variable_name; <type B> shorter_var_name; <type C> even_shorter; <type D> i;

• if (*val == 0)

• if (val == 0)

if (!val)

return;

• first_bit = find_first_bit(val, cbm_len);
• zero_bit = find_next_zero_bit(val, cbm_len, first_bit);

• first_bit = find_first_bit(&val, cbm_len);
• zero_bit = find_next_zero_bit(&val, cbm_len, first_bit);

/* Clear any remaining bits to ensure contiguous region */

• bitmap_clear(val, zero_bit, cbm_len - zero_bit);

• bitmap_clear(&val, zero_bit, cbm_len - zero_bit);
• *_val = (u32)val;

... and also, that function should simply return the u32 value instead of using @_val as an input and output var.

But that should be a separate cleanup patch anyway.

Thx.