linux-kernel - Re: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing shadow stack

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Message-ID: <04800c52-1f86-c485-ba7c-2216d8c4966f@linux.intel.com>
Date:   Tue, 10 Jul 2018 16:10:08 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>, 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>,
        Cyrill Gorcunov <gorcunov@...il.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@...omiun.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing
 shadow stack

On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>

This still needs a changelog, even if you think it's simple.
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -446,6 +446,15 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
>  	error = -ENOMEM;
>  	if (!vma)
>  		goto out;
> +
> +	/*
> +	 * Do not allow changing shadow stack memory.
> +	 */
> +	if (vma->vm_flags & VM_SHSTK) {
> +		error = -EINVAL;
> +		goto out;
> +	}
> +

I think this is a _bit_ draconian.  Why shouldn't we be able to use
protection keys with a shadow stack?  Or, set it to PROT_NONE?