Re: [PATCH] kernel: sys: fix potential Spectre v1

From: Peter Zijlstra <peterz@infradead.org>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>
Subject: Re: [PATCH] kernel: sys: fix potential Spectre v1
Date: Wed, 23 May 2018 11:08:40 +0200	[thread overview]
Message-ID: <20180523090840.GU12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <112349fb-837c-7b91-e256-a1c443710150@embeddedor.com>

Sorry for being late to the party..

On Wed, May 23, 2018 at 12:03:57AM -0500, Gustavo A. R. Silva wrote:

> +#define validate_index_nospec(index, size)                            \
> +({                                                                    \
> +       bool ret = true;                                               \
> +       typeof(index) *ptr = &(index);                                 \
> +       typeof(size) _s = (size);                                      \
> +                                                                      \
> +       BUILD_BUG_ON(sizeof(*ptr) > sizeof(long));                     \
> +       BUILD_BUG_ON(sizeof(_s) > sizeof(long));                       \
> +                                                                      \
> +       if (*ptr >= size)                                              \
> +               ret = false;                                           \
> +                                                                      \
> +       *ptr = array_index_nospec(*ptr, _s);                           \
> +                                                                      \
> +       ret;                                                           \
> +})

Would not something like:

	bool ret = false;

	....

	if (*ptr < _s) {
		*ptr = array_index_nospec(*ptr, _s);
		ret = true;
	}

	ret;

be more obvious?