Re: next-20170515: WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:236 note_page+0x630/0x7e0

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, May 19, 2017 at 05:40:16PM +0200, Luis R. Rodriguez wrote:
> If the following is a legit forced way to get query the kernel to ask it 
> who owns a page then perhaps this technique can be used in the future to
> figure out who the hell caused this. Catalin, can you confirm? In this
> case this is perhaps not a leaked page but I am trying to abuse the
> kmemleak debugfs API to query who allocated the page. Is that fine?
> 
> [    0.916771] WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:235 note_page+0x63c/0x7e0
> [    0.917636] x86/mm: Found insecure W+X mapping at address ffffffffc03d5000/0xffffffffc03d5000
> [    0.918502] Modules linked in:
> [    0.918819] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.11.0-mcgrof-force-config #340
> [    0.919631] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
> [    0.920011] Call Trace:
> [    0.920011]  dump_stack+0x63/0x81
> [    0.920011]  __warn+0xcb/0xf0
> [    0.920011]  warn_slowpath_fmt+0x5a/0x80
> [    0.920011]  note_page+0x63c/0x7e0
> [    0.920011]  ptdump_walk_pgd_level_core+0x3b1/0x460
> [    0.920011]  ? 0xffffffff86c00000
> [    0.920011]  ptdump_walk_pgd_level_checkwx+0x17/0x20
> [    0.920011]  mark_rodata_ro+0xf4/0x100
> [    0.920011]  ? rest_init+0x80/0x80
> [    0.920011]  kernel_init+0x2a/0x100
> [    0.920011]  ret_from_fork+0x2c/0x40
> [    0.925474] ---[ end trace dca00cd779490a2b ]---
> [    0.925959] x86/mm: Checked W+X mappings: FAILED, 1 W+X pages found.
> 
> echo dump=0xffffffffc03d5000 > /sys/kernel/debug/kmemleak
> dmesg | tail
> 
> [   49.209565] kmemleak: Object 0xffffffffc03d5000 (size 335):
> [   49.210814] kmemleak:   comm "swapper/0", pid 1, jiffies 4294892440
> [   49.212148] kmemleak:   min_count = 2
> [   49.212852] kmemleak:   count = 0
> [   49.213363] kmemleak:   flags = 0x1
> [   49.213363] kmemleak:   checksum = 0
> [   49.213363] kmemleak:   backtrace:
> [   49.213363]      kmemleak_alloc+0x4a/0xa0
> [   49.213363]      __vmalloc_node_range+0x20a/0x2b0
> [   49.213363]      module_alloc+0x67/0xc0
> [   49.213363]      arch_ftrace_update_trampoline+0xba/0x260
> [   49.213363]      ftrace_startup+0x90/0x210
> [   49.213363]      register_ftrace_function+0x4b/0x60
> [   49.213363]      arm_kprobe+0x84/0xe0
> [   49.213363]      register_kprobe+0x56e/0x5b0
> [   49.213363]      init_test_probes+0x61/0x560
> [   49.213363]      init_kprobes+0x1e3/0x206
> [   49.213363]      do_one_initcall+0x52/0x1a0
> [   49.213363]      kernel_init_freeable+0x178/0x200
> [   49.213363]      kernel_init+0xe/0x100
> [   49.213363]      ret_from_fork+0x2c/0x40
> [   49.213363]      0xffffffffffffffff

You could as well use kmemleak this way since it tracks the memory
allocations. However, it doesn't track alloc_pages and also doesn't
track mapping existing pages (vmap etc.)

-- 
Catalin