Re: [PATCH] mm: page_alloc: fix page_poison=1 / INIT_ON_ALLOC_DEFAULT_ON interaction
From: Kees Cook <hidden>
Date: 2021-07-14 03:10:06
Also in:
lkml
Subsystem:
memory management, memory management - page allocator, the rest · Maintainers:
Andrew Morton, Vlastimil Babka, Linus Torvalds
On Mon, Jul 12, 2021 at 10:58:16PM +0100, Sergei Trofimovich wrote:
To reproduce the failure we need the following system:
- kernel command: page_poison=1 init_on_free=0 init_on_alloc=0
- kernel config:
* CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y
* CONFIG_INIT_ON_FREE_DEFAULT_ON=y
* CONFIG_PAGE_POISONING=y
0000000085629bdd: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0000000022861832: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000000c597f5b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
CPU: 11 PID: 15195 Comm: bash Kdump: loaded Tainted: G U O 5.13.1-gentoo-x86_64 #1
Hardware name: System manufacturer System Product Name/PRIME Z370-A, BIOS 2801 01/13/2021
Call Trace:
dump_stack+0x64/0x7c
__kernel_unpoison_pages.cold+0x48/0x84
post_alloc_hook+0x60/0xa0
get_page_from_freelist+0xdb8/0x1000
__alloc_pages+0x163/0x2b0
__get_free_pages+0xc/0x30
pgd_alloc+0x2e/0x1a0
? dup_mm+0x37/0x4f0
mm_init+0x185/0x270
dup_mm+0x6b/0x4f0
? __lock_task_sighand+0x35/0x70
copy_process+0x190d/0x1b10
kernel_clone+0xba/0x3b0
__do_sys_clone+0x8f/0xb0
do_syscall_64+0x68/0x80
? do_syscall_64+0x11/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
Before the 51cba1eb ("init_on_alloc: Optimize static branches")
init_on_alloc never enabled static branch by default. It could
only be enabed explicitly by init_mem_debugging_and_hardening().But init_mem_debugging_and_hardening() is always called (by mm_init()).
quoted hunk ↗ jump to hunk
But after the 51cba1eb static branch could already be enabled by default. There was no code to ever disable it. That caused page_poison=1 / init_on_free=1 conflict. This change extends init_mem_debugging_and_hardening() to also disable static branch disabling. CC: Andrew Morton <akpm@linux-foundation.org> CC: Kees Cook <redacted> CC: Alexander Potapenko <glider@google.com> CC: Thomas Gleixner <redacted> CC: Vlastimil Babka <redacted> CC: linux-mm@kvack.org Reported-by: bowsingbetee@pm.me Reported-by: Mikhail Morfikov Fixes: 51cba1eb ("init_on_alloc: Optimize static branches") Signed-off-by: Sergei Trofimovich <redacted> --- mm/page_alloc.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3b97e17806be..46cb4a9c2b50 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c@@ -840,18 +840,22 @@ void init_mem_debugging_and_hardening(void) } #endif - if (_init_on_alloc_enabled_early) { - if (page_poisoning_requested) + if (_init_on_alloc_enabled_early || + IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON)) {
This doesn't look right. _init_on_alloc_enabled_early already has the
same value:
static bool _init_on_alloc_enabled_early __read_mostly
= IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON);
So checking this is just a side-effect of how static_branch_maybe()
happens to be behaving.
+ if (page_poisoning_requested) {
pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
"will take precedence over init_on_alloc\n");
- else
+ static_branch_disable(&init_on_alloc);
+ } else
static_branch_enable(&init_on_alloc);
}
- if (_init_on_free_enabled_early) {
- if (page_poisoning_requested)
+ if (_init_on_free_enabled_early ||
+ IS_ENABLED(CONFIG_INIT_ON_FREE_DEFAULT_ON)) {
+ if (page_poisoning_requested) {
pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
"will take precedence over init_on_free\n");
- else
+ static_branch_disable(&init_on_free);
+ } else
static_branch_enable(&init_on_free);
}I think it would be better to clean this up without additional confusion involving the CONFIGs:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3b97e17806be..1f19365bc158 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c@@ -840,21 +840,24 @@ void init_mem_debugging_and_hardening(void) } #endif - if (_init_on_alloc_enabled_early) { - if (page_poisoning_requested) - pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " - "will take precedence over init_on_alloc\n"); - else - static_branch_enable(&init_on_alloc); - } - if (_init_on_free_enabled_early) { - if (page_poisoning_requested) - pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " - "will take precedence over init_on_free\n"); - else - static_branch_enable(&init_on_free); + if ((_init_on_alloc_enabled_early || _init_on_free_enabled_early) && + page_poisoning_requested) { + pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, " + "will take precedence over init_on_alloc and init_on_free\n"); + _init_on_alloc_enabled_early = false; + _init_on_free_enabled_early = false; } + if (_init_on_alloc_enabled_early) + static_branch_enable(&init_on_alloc); + else + static_branch_disable(&init_on_alloc); + + if (_init_on_free_enabled_early) + static_branch_enable(&init_on_free); + else + static_branch_disable(&init_on_free); + #ifdef CONFIG_DEBUG_PAGEALLOC if (!debug_pagealloc_enabled()) return;
--
Kees Cook