Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of access_ok

From: Oleg Nesterov <oleg@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Gregory Price <gourry.memverge@gmail.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Linux-Arch <linux-arch@vger.kernel.org>,
	avagin@gmail.com, Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	krisman@collabora.com, Thomas Gleixner <tglx@linutronix.de>,
	Jonathan Corbet <corbet@lwn.net>, shuah <shuah@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	tongtiangen@huawei.com, Robin Murphy <robin.murphy@arm.com>,
	Gregory Price <gregory.price@memverge.com>
Subject: Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of access_ok
Date: Wed, 29 Mar 2023 18:03:23 +0200	[thread overview]
Message-ID: <20230329160322.GA4477@redhat.com> (raw)
In-Reply-To: <9a456346-e207-44e1-873e-40d21334e01b@app.fastmail.com>

On 03/29, Arnd Bergmann wrote:
>
> On Wed, Mar 29, 2023, at 17:15, Oleg Nesterov wrote:
> >
> > This look as if access_ok() or __access_ok() doesn't depend on task, but
> > this is not true in general. Say, TASK_SIZE_MAX can check is_32bit_task()
> > test_thread_flag(TIF_32BIT...) and this uses "current".
> >
> > Again, we probably do not care, but I don't like the fact task_access_ok()
> > looks as if task_access_ok(task) returns the same result as "task" calling
> > access_ok().
>
> I think the idea of TASK_SIZE_MAX is that it is a compile-time constant and in fact independent of current, while TASK_SIZE
> takes TIF_32BIT into account.

Say, arch/loongarch defines TASK_SIZE which depends on test_thread_flag(TIF_32BIT_ADDR)
but it doesn't define TASK_SIZE_MAX, so __access_ok() will use TASK_SIZE.

Oleg.