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Date:   Wed, 22 Sep 2021 09:30:12 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Peter Collingbourne <pcc@google.com>
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Subject: Re: [PATCH] kernel: introduce prctl(PR_LOG_UACCESS)
Message-ID: <YUrNdPLh+keAKPUy@grain>
References: <20210922061809.736124-1-pcc@google.com>
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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.