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SubjectRe: [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.

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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