linux-kernel - Re: [PATCH v7 4/4] vsprintf: Add command line option debug_boot_weak

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Date:   Wed, 13 Jun 2018 14:46:01 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 4/4] vsprintf: Add command line option
 debug_boot_weak_hash

On Tue, 12 Jun 2018 10:39:14 +1000
"Tobin C. Harding" <me@...in.cc> wrote:


> +/* Make pointers available for printing early in the boot sequence. */
> +static int debug_boot_weak_hash __ro_after_init;
> +EXPORT_SYMBOL(debug_boot_weak_hash);
> +
> +static int __init debug_boot_weak_hash_enable(char *str)
> +{
> +	debug_boot_weak_hash = 1;
> +	pr_info("debug_boot_weak_hash enabled\n");
> +	return 0;
> +}
> +early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);
> +
>  static DEFINE_STATIC_KEY_TRUE(not_filled_random_ptr_key);
>  static siphash_key_t ptr_key __read_mostly;
>  
> @@ -1703,6 +1715,12 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
>  	const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";
>  	unsigned long hashval;
>  
> +	/* When debugging early boot use non-cryptographically secure hash */
> +	if (unlikely(debug_boot_weak_hash)) {

I was hoping to find a way to make the debug_boot_weak_hash into a
static_branch, but its setting is too early to have for a jump label.

I toyed with nesting this inside a static_branch too, but it seems too
much overkill.

Hence, I'll just punt and accept this patch as is ;-)

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> +		hashval = hash_long((unsigned long)ptr, 32);
> +		return pointer_string(buf, end, (const void *)hashval, spec);
> +	}
> +
>  	if (static_branch_unlikely(&not_filled_random_ptr_key)) {
>  		spec.field_width = 2 * sizeof(ptr);
>  		/* string length must be less than default_width */