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SubjectRe: [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@tobin.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@goodmis.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 */

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