[PATCH] mm: page_alloc: fix page_poison=1 / INIT_ON_ALLOC_DEFAULT_ON interaction

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 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)) {
+		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);
 	}
 

-- 
2.32.0