kfence: Fix wrong size of alloc_covered when enable dynamic

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4V388


CVE: NA

--------------------------------

Patch "kfence: Add a module parameter to adjust kfence objects"
enable dynamic configuration of the number of KFENCE guarded
objects, but the size of alloc_covered is not the same with the
original kfence. This is because const_ilog2 is just valid for
a constant, and KFENCE_NR_OBJECTS is not a constant when enabling
dynamic configuration.

This difference between original kfence will lead to a confusion
loggic in the process of skipping covered path. In a arm64 machine,
the following panic is observed.

  Call trace:
   __kfence_alloc+0x378/0x780
   kmem_cache_alloc+0x204/0x614
   getname_kernel+0x38/0xf4
   filp_open+0x2c/0x6c
   populate_rootfs+0xcc/0x174
   do_one_initcall+0xac/0x20c
   kernel_init_freeable+0x380/0x3c8
   kernel_init+0x18/0xf0
   ret_from_fork+0x10/0x18
  Code: 54000080 a9400381 f9000420 f9000001 (f900039c)
  ---[ end trace 814fe40d608e1b74 ]---
  Kernel panic - not syncing: TLB conflict abort: Fatal exception

To fix this, ilog2 is used to replace const_ilog2 when enable
dynamic configuration of KFENCE guarded objects.

Fixes: 901b983c ("kfence: Add a module parameter to adjust kfence objects")
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>