Re: [PATCH] kernel: introduce prctl(PR_LOG_UACCESS)

From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Peter Collingbourne <pcc@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Sami Tolvanen <samitolvanen@google.com>,
	YiFei Zhu <yifeifz2@illinois.edu>,
	Colin Ian King <colin.king@canonical.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Gabriel Krisman Bertazi <krisman@collabora.com>,
	Balbir Singh <sblbir@amazon.com>,
	Chris Hyser <chris.hyser@oracle.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	Arnd Bergmann <arnd@arndb.de>, Dmitry Vyukov <dvyukov@google.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Alexey Gladkov <legion@kernel.org>,
	Ran Xiaokai <ran.xiaokai@zte.com.cn>,
	David Hildenbrand <david@redhat.com>,
	Xiaofeng Cao <caoxiaofeng@yulong.com>,
	Thomas Cedeno <thomascedeno@google.com>,
	Marco Elver <elver@google.com>,
	Alexander Potapenko <glider@google.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Evgenii Stepanov <eugenis@google.com>
Subject: Re: [PATCH] kernel: introduce prctl(PR_LOG_UACCESS)
Date: Wed, 22 Sep 2021 09:30:12 +0300	[thread overview]
Message-ID: <YUrNdPLh+keAKPUy@grain> (raw)
In-Reply-To: <20210922061809.736124-1-pcc@google.com>

On Tue, Sep 21, 2021 at 11:18:09PM -0700, Peter Collingbourne wrote:
> This patch introduces a kernel feature known as uaccess logging.
> With uaccess logging, the userspace program passes the address and size
> of a so-called uaccess buffer to the kernel via a prctl(). The prctl()
> is a request for the kernel to log any uaccesses made during the next
> syscall to the uaccess buffer. When the next syscall returns, the address
> one past the end of the logged uaccess buffer entries is written to the
> location specified by the third argument to the prctl(). In this way,
> the userspace program may enumerate the uaccesses logged to the access
> buffer to determine which accesses occurred.
...
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e12b524426b0..3fecb0487b97 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -34,6 +34,7 @@
>  #include <linux/rseq.h>
>  #include <linux/seqlock.h>
>  #include <linux/kcsan.h>
> +#include <linux/uaccess_buffer_info.h>
>  #include <asm/kmap_size.h>
>  
>  /* task_struct member predeclarations (sorted alphabetically): */
> @@ -1487,6 +1488,8 @@ struct task_struct {
>  	struct callback_head		l1d_flush_kill;
>  #endif
>  
> +	struct uaccess_buffer_info	uaccess_buffer;
> +

Hi, Peter! I didn't read the patch carefully yet (will do once time permit)
but from a glance should not this member be under #ifdef CONFIG_UACCESS_BUFFER
or something? task_struct is already bloated too much :(

> +	case PR_LOG_UACCESS:
> +		if (arg5)
> +			return -EINVAL;
> +		error = uaccess_buffer_set_logging(arg2, arg3, arg4);
> +		break;

Same here (if only I didn't miss something obvious). If there is no support
for CONFIG_UACCESS_BUFFER we should return an error I guess.