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Date:   Tue, 13 Jul 2021 20:21:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Sergei Trofimovich <slyfox@...too.org>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        bowsingbetee@...me, Mikhail Morfikov <mmorfikov@...il.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] mm: page_alloc: Fix page_poison=1 /
 INIT_ON_ALLOC_DEFAULT_ON interaction

On Tue, Jul 13, 2021 at 08:19:35PM -0700, Kees Cook wrote:
> From: Sergei Trofimovich <slyfox@...too.org>
> 
> 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: Alexander Potapenko <glider@...gle.com>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Vlastimil Babka <vbabka@...e.cz>
> CC: linux-mm@...ck.org
> Reported-by: bowsingbetee@...me
> Reported-by: Mikhail Morfikov <mmorfikov@...il.com>
> Fixes: 51cba1ebc60d ("init_on_alloc: Optimize static branches")
> Cc: stable@...r.kernelo.org

yay typo "kernelo". Andrew, are you able to clean this up, or should I send a v3?

Sorry!

-Kees

> Signed-off-by: Sergei Trofimovich <slyfox@...too.org>
> Link: https://lore.kernel.org/r/20210712215816.1512739-1-slyfox@gentoo.org
> Co-developed-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  mm/page_alloc.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
> 
> 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;
> -- 
> 2.30.2
> 

-- 
Kees Cook

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