linux/arch/powerpc
Michael Ellerman a984506c54 powerpc/mm: Don't report PUDs as memory leaks when using kmemleak
Paul Menzel reported that kmemleak was producing reports such as:

  unreferenced object 0xc0000000f8b80000 (size 16384):
    comm "init", pid 1, jiffies 4294937416 (age 312.240s)
    hex dump (first 32 bytes):
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    backtrace:
      [<00000000d997deb7>] __pud_alloc+0x80/0x190
      [<0000000087f2e8a3>] move_page_tables+0xbac/0xdc0
      [<00000000091e51c2>] shift_arg_pages+0xc0/0x210
      [<00000000ab88670c>] setup_arg_pages+0x22c/0x2a0
      [<0000000060871529>] load_elf_binary+0x41c/0x1648
      [<00000000ecd9d2d4>] search_binary_handler.part.11+0xbc/0x280
      [<0000000034e0cdd7>] __do_execve_file.isra.13+0x73c/0x940
      [<000000005f953a6e>] sys_execve+0x58/0x70
      [<000000009700a858>] system_call+0x5c/0x70

Indicating that a PUD was being leaked.

However what's really happening is that kmemleak is not able to
recognise the references from the PGD to the PUD, because they are not
fully qualified pointers.

We can confirm that in xmon, eg:

Find the task struct for pid 1 "init":
  0:mon> P
       task_struct     ->thread.ksp    PID   PPID S  P CMD
  c0000001fe7c0000 c0000001fe803960      1      0 S 13 systemd

Dump virtual address 0 to find the PGD:
  0:mon> dv 0 c0000001fe7c0000
  pgd  @ 0xc0000000f8b01000

Dump the memory of the PGD:
  0:mon> d c0000000f8b01000
  c0000000f8b01000 00000000f8b90000 0000000000000000  |................|
  c0000000f8b01010 0000000000000000 0000000000000000  |................|
  c0000000f8b01020 0000000000000000 0000000000000000  |................|
  c0000000f8b01030 0000000000000000 00000000f8b80000  |................|
                                    ^^^^^^^^^^^^^^^^

There we can see the reference to our supposedly leaked PUD. But
because it's missing the leading 0xc, kmemleak won't recognise it.

We can confirm it's still in use by translating an address that is
mapped via it:
  0:mon> dv 7fff94000000 c0000001fe7c0000
  pgd  @ 0xc0000000f8b01000
  pgdp @ 0xc0000000f8b01038 = 0x00000000f8b80000 <--
  pudp @ 0xc0000000f8b81ff8 = 0x00000000037c4000
  pmdp @ 0xc0000000037c5ca0 = 0x00000000fbd89000
  ptep @ 0xc0000000fbd89000 = 0xc0800001d5ce0386
  Maps physical address = 0x00000001d5ce0000
  Flags = Accessed Dirty Read Write

The fix is fairly simple. We need to tell kmemleak to ignore PUD
allocations and never report them as leaks. We can also tell it not to
scan the PGD, because it will never find pointers in there. However it
will still notice if we allocate a PGD and then leak it.

Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-07-30 22:48:21 +10:00
..
boot powerpc/dts: Use a correct at24 compatible fallback in ac14xx 2018-07-10 10:58:40 +10:00
configs powerpc: Add ppc32_allmodconfig defconfig target 2018-07-24 22:03:15 +10:00
crypto powerpc: move ASM_CONST and stringify_in_c() into asm-const.h 2018-07-30 22:48:16 +10:00
include powerpc/mm: Don't report PUDs as memory leaks when using kmemleak 2018-07-30 22:48:21 +10:00
kernel powerpc: declare set_breakpoint() static 2018-07-30 22:48:18 +10:00
kvm powerpc: remove unnecessary inclusion of asm/tlbflush.h 2018-07-30 22:48:20 +10:00
lib powerpc: clean inclusions of asm/feature-fixups.h 2018-07-30 22:48:17 +10:00
math-emu License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mm powerpc: remove unnecessary inclusion of asm/tlbflush.h 2018-07-30 22:48:20 +10:00
net powerpc: move ASM_CONST and stringify_in_c() into asm-const.h 2018-07-30 22:48:16 +10:00
oprofile treewide: kzalloc() -> kcalloc() 2018-06-12 16:19:22 -07:00
perf powerpc: clean the inclusion of stringify.h 2018-07-30 22:48:17 +10:00
platforms powerpc: remove unnecessary inclusion of asm/tlbflush.h 2018-07-30 22:48:20 +10:00
purgatory powerpc: move ASM_CONST and stringify_in_c() into asm-const.h 2018-07-30 22:48:16 +10:00
sysdev powerpc: remove unnecessary inclusion of asm/tlbflush.h 2018-07-30 22:48:20 +10:00
tools powerpc/kbuild: move -mprofile-kernel check to Kconfig 2018-06-11 09:16:29 +09:00
xmon powerpc: move ASM_CONST and stringify_in_c() into asm-const.h 2018-07-30 22:48:16 +10:00
Kconfig powerpc: Enable kernel XZ compression option on BOOK3S_32 2018-07-04 22:41:10 +10:00
Kconfig.debug powerpc: Add new kconfig CONFIG_PPC_IRQ_SOFT_MASK_DEBUG 2018-01-19 22:37:03 +11:00
Makefile powerpc: Add ppc64le and ppc64_book3e allmodconfig targets 2018-07-24 22:03:16 +10:00
Makefile.postlink License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00