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

Resulting in:

    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
     mm_init+0x185/0x270
     dup_mm+0x6b/0x4f0
     copy_process+0x190d/0x1b10
     kernel_clone+0xba/0x3b0
     __do_sys_clone+0x8f/0xb0
     do_syscall_64+0x68/0x80
     entry_SYSCALL_64_after_hwframe+0x44/0xae

Before commit 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 commit 51cba1eb, a 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.

Link: https://lkml.kernel.org/r/20210714031935.4094114-1-keescook@chromium.org
Link: https://lore.kernel.org/r/20210712215816.1512739-1-slyfox@gentoo.org
Fixes: 51cba1eb ("init_on_alloc: Optimize static branches")
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Co-developed-by: Kees Cook <keescook@chromium.org>
Reported-by: Mikhail Morfikov <mmorfikov@gmail.com>
Reported-by: <bowsingbetee@pm.me>
Tested-by: <bowsingbetee@protonmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -840,20 +840,23 @@ void init_mem_debugging_and_hardening(void)
 	}
 #endif
 
-	if (_init_on_alloc_enabled_early) {
-		if (page_poisoning_requested)
+	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\n");
-		else
-			static_branch_enable(&init_on_alloc);
+			"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_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");
+
+	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())