linux-kernel - Re: [PATCH v7 07/14] x86/cet/ibt: Add arch

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Date:   Fri, 7 Jun 2019 10:07:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v7 07/14] x86/cet/ibt: Add arch_prctl functions for IBT

On Thu, Jun 06, 2019 at 01:09:19PM -0700, Yu-cheng Yu wrote:

> +static int handle_bitmap(unsigned long arg2)
> +{
> +	unsigned long addr, size;
> +
> +	if (get_user(addr, (unsigned long __user *)arg2) ||
> +	    get_user(size, (unsigned long __user *)arg2 + 1))
> +		return -EFAULT;
> +
> +	return cet_setup_ibt_bitmap(addr, size);
> +}


> +	/*
> +	 * Allocate legacy bitmap and return address & size to user.
> +	 */
> +	case ARCH_X86_CET_SET_LEGACY_BITMAP:
> +		return handle_bitmap(arg2);

AFAICT it does exactly the opposite of that comment; it gets the address
and size from userspace and doesn't allocate anything at all.