mm: kmemleak: take a full lowmem check in kmemleak_*_phys()

mm: kmemleak: take a full lowmem check in kmemleak_*_phys()

The kmemleak_*_phys() apis do not check the address for lowmem's min
boundary, while the caller may pass an address below lowmem, which will
trigger an oops:

# echo scan > /sys/kernel/debug/kmemleak
[   54.888353] Unable to handle kernel paging request at virtual address ff5fffffffe00000
[   54.888932] Oops [#1]
[   54.889102] Modules linked in:
[   54.889326] CPU: 2 PID: 134 Comm: bash Not tainted 5.18.0-rc1-next-20220407 #33
[   54.889620] Hardware name: riscv-virtio,qemu (DT)
[   54.889901] epc : scan_block+0x74/0x15c
[   54.890215]  ra : scan_block+0x72/0x15c
[   54.890390] epc : ffffffff801e5806 ra : ffffffff801e5804 sp : ff200000104abc30
[   54.890607]  gp : ffffffff815cd4e8 tp : ff60000004cfa340 t0 : 0000000000000200
[   54.890835]  t1 : 00aaaaaac23954cc t2 : 00000000000003ff s0 : ff200000104abc90
[   54.891024]  s1 : ffffffff81b0ff28 a0 : 0000000000000000 a1 : ff5fffffffe01000
[   54.891201]  a2 : ffffffff81b0ff28 a3 : 0000000000000002 a4 : 0000000000000001
[   54.891377]  a5 : 0000000000000000 a6 : ff200000104abd7c a7 : 0000000000000005
[   54.891552]  s2 : ff5fffffffe00ff9 s3 : ffffffff815cd998 s4 : ffffffff815d0e90
[   54.891727]  s5 : ffffffff81b0ff28 s6 : 0000000000000020 s7 : ffffffff815d0eb0
[   54.891903]  s8 : ffffffffffffffff s9 : ff5fffffffe00000 s10: ff5fffffffe01000
[   54.892078]  s11: 0000000000000022 t3 : 00ffffffaa17db4c t4 : 000000000000000f
[   54.892271]  t5 : 0000000000000001 t6 : 0000000000000000
[   54.892408] status: 0000000000000100 badaddr: ff5fffffffe00000 cause: 000000000000000d
[   54.892643] [<ffffffff801e5a1c>] scan_gray_list+0x12e/0x1a6
[   54.892824] [<ffffffff801e5d3e>] kmemleak_scan+0x2aa/0x57e
[   54.892961] [<ffffffff801e633c>] kmemleak_write+0x32a/0x40c
[   54.893096] [<ffffffff803915ac>] full_proxy_write+0x56/0x82
[   54.893235] [<ffffffff801ef456>] vfs_write+0xa6/0x2a6
[   54.893362] [<ffffffff801ef880>] ksys_write+0x6c/0xe2
[   54.893487] [<ffffffff801ef918>] sys_write+0x22/0x2a
[   54.893609] [<ffffffff8000397c>] ret_from_syscall+0x0/0x2
[   54.894183] ---[ end trace 0000000000000000 ]---

So check the address for lowmem's min boundary.

Link: https://lkml.kernel.org/r/20220413122925.33856-1-patrick.wang.shcn@gmail.com
Signed-off-by: Patrick Wang <patrick.wang.shcn@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>