Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Feedback-ID: i56a14606:Fastmail
User-Agent: Cyrus-JMAP/3.9.0-alpha0-531-gfdfa13a06d-fm-20230703.001-gfdfa13a0
Mime-Version: 1.0
Message-Id: <6a49b585-05d0-4b79-b5ab-d710f5d6d598@app.fastmail.com>
In-Reply-To: <20230721105743.819362688@infradead.org>
References: <20230721102237.268073801@infradead.org>
 <20230721105743.819362688@infradead.org>
Date:   Fri, 21 Jul 2023 17:47:31 +0200
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Peter Zijlstra" <peterz@infradead.org>,
        "Thomas Gleixner" <tglx@linutronix.de>,
        "Jens Axboe" <axboe@kernel.dk>
Cc:     linux-kernel@vger.kernel.org, "Ingo Molnar" <mingo@redhat.com>,
        "Darren Hart" <dvhart@infradead.org>, dave@stgolabs.net,
        andrealmeid@igalia.com,
        "Andrew Morton" <akpm@linux-foundation.org>, urezki@gmail.com,
        "Christoph Hellwig" <hch@infradead.org>,
        "Lorenzo Stoakes" <lstoakes@gmail.com>, linux-api@vger.kernel.org,
        linux-mm@kvack.org, Linux-Arch <linux-arch@vger.kernel.org>,
        malteskarupke@web.de
Subject: Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags
Content-Type: text/plain
Precedence: bulk

On Fri, Jul 21, 2023, at 12:22, Peter Zijlstra wrote:
>   * futex_parse_waitv - Parse a waitv array from userspace
> @@ -207,7 +207,12 @@ static int futex_parse_waitv(struct fute
>  		if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved)
>  			return -EINVAL;
> 
> -		if (!(aux.flags & FUTEX2_32))
> +		if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
> +			if ((aux.flags & FUTEX2_64) == FUTEX2_64)
> +				return -EINVAL;
> +		}
> +
> +		if ((aux.flags & FUTEX2_64) != FUTEX2_32)
>  			return -EINVAL;

This looks slightly confusing, how about defining another
FUTEX2_SIZEMASK (or similar) macro to clarify that
"aux.flags & FUTEX2_64" is a mask operation that can
match the FUTEX2_{8,16,32,64} values?

       Arnd