From 311ade0eab192f0abee2f70bce761bf0d66990c4 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Wed, 20 Feb 2019 22:19:45 -0800 Subject: [PATCH] mm/debug.c: fix __dump_page() for poisoned pages Evaluating page_mapping() on a poisoned page ends up dereferencing junk and making PF_POISONED_CHECK() considerably crashier than intended: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000006 Mem abort info: ESR = 0x96000005 Exception class = DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000005 CM = 0, WnR = 0 user pgtable: 4k pages, 39-bit VAs, pgdp = 00000000c2f6ac38 [0000000000000006] pgd=0000000000000000, pud=0000000000000000 Internal error: Oops: 96000005 [#1] PREEMPT SMP Modules linked in: CPU: 2 PID: 491 Comm: bash Not tainted 5.0.0-rc1+ #1 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Dec 17 2018 pstate: 00000005 (nzcv daif -PAN -UAO) pc : page_mapping+0x18/0x118 lr : __dump_page+0x1c/0x398 Process bash (pid: 491, stack limit = 0x000000004ebd4ecd) Call trace: page_mapping+0x18/0x118 __dump_page+0x1c/0x398 dump_page+0xc/0x18 remove_store+0xbc/0x120 dev_attr_store+0x18/0x28 sysfs_kf_write+0x40/0x50 kernfs_fop_write+0x130/0x1d8 __vfs_write+0x30/0x180 vfs_write+0xb4/0x1a0 ksys_write+0x60/0xd0 __arm64_sys_write+0x18/0x20 el0_svc_common+0x94/0xf8 el0_svc_handler+0x68/0x70 el0_svc+0x8/0xc Code: f9400401 d1000422 f240003f 9a801040 (f9400402) ---[ end trace cdb5eb5bf435cecb ]--- Fix that by not inspecting the mapping until we've determined that it's likely to be valid. Now the above condition still ends up stopping the kernel, but in the correct manner: page:ffffffbf20000000 is uninitialized and poisoned raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) ------------[ cut here ]------------ kernel BUG at ./include/linux/mm.h:1006! Internal error: Oops - BUG: 0 [#1] PREEMPT SMP Modules linked in: CPU: 1 PID: 483 Comm: bash Not tainted 5.0.0-rc1+ #3 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Dec 17 2018 pstate: 40000005 (nZcv daif -PAN -UAO) pc : remove_store+0xbc/0x120 lr : remove_store+0xbc/0x120 ... Link: http://lkml.kernel.org/r/03b53ee9d7e76cda4b9b5e1e31eea080db033396.1550071778.git.robin.murphy@arm.com Fixes: 1c6fb1d89e73 ("mm: print more information about mapping in __dump_page") Signed-off-by: Robin Murphy Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/debug.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/debug.c b/mm/debug.c index 0abb987dad9b..1611cf00a137 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -44,7 +44,7 @@ const struct trace_print_flags vmaflag_names[] = { void __dump_page(struct page *page, const char *reason) { - struct address_space *mapping = page_mapping(page); + struct address_space *mapping; bool page_poisoned = PagePoisoned(page); int mapcount; @@ -58,6 +58,8 @@ void __dump_page(struct page *page, const char *reason) goto hex_only; } + mapping = page_mapping(page); + /* * Avoid VM_BUG_ON() in page_mapcount(). * page->_mapcount space in struct page is used by sl[aou]b pages to -- 2.30.2