linux-kernel - Re: [PATCH v2 2/3] lib, uaccess: add failure injection to usercopy functions

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Date:   Mon, 31 Aug 2020 18:21:50 +0200
From:   peterz@...radead.org
To:     albert.linde@...il.com
Cc:     akpm@...ux-foundation.org, bp@...en8.de, mingo@...hat.com,
        corbet@....net, tglx@...utronix.de, arnd@...db.de,
        akinobu.mita@...il.com, hpa@...or.com, viro@...iv.linux.org.uk,
        glider@...gle.com, andreyknvl@...gle.com, dvyukov@...gle.com,
        elver@...gle.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        x86@...nel.org, Albert van der Linde <alinde@...gle.com>
Subject: Re: [PATCH v2 2/3] lib, uaccess: add failure injection to usercopy
 functions

On Fri, Aug 28, 2020 at 02:13:43PM +0000, albert.linde@...il.com wrote:
> @@ -82,6 +83,8 @@ __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
>  static __always_inline __must_check unsigned long
>  __copy_from_user(void *to, const void __user *from, unsigned long n)
>  {
> +	if (should_fail_usercopy())
> +		return n;
>  	might_fault();
>  	instrument_copy_from_user(to, from, n);
>  	check_object_size(to, n, false);

> @@ -124,7 +131,7 @@ _copy_from_user(void *to, const void __user *from, unsigned long n)
>  {
>  	unsigned long res = n;
>  	might_fault();
> -	if (likely(access_ok(from, n))) {
> +	if (!should_fail_usercopy() && likely(access_ok(from, n))) {
>  		instrument_copy_from_user(to, from, n);
>  		res = raw_copy_from_user(to, from, n);
>  	}

You're inconsistent with your order against might_fault() throughout the
patch. After is the right place.