linux-kernel - Re: [PATCH v11 25/25] x86/cet/shstk: Add arch

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Message-ID: <87ft892vvf.fsf@oldenburg2.str.redhat.com>
Date:   Wed, 26 Aug 2020 18:51:48 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     "Yu\, Yu-cheng" <yu-cheng.yu@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list\:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        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>,
        "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>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>
Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

* Dave Martin:

> On Tue, Aug 25, 2020 at 04:34:27PM -0700, Yu, Yu-cheng wrote:
>> On 8/25/2020 4:20 PM, Dave Hansen wrote:
>> >On 8/25/20 2:04 PM, Yu, Yu-cheng wrote:
>> >>>>I think this is more arch-specific.  Even if it becomes a new syscall,
>> >>>>we still need to pass the same parameters.
>> >>>
>> >>>Right, but without the copying in and out of memory.
>> >>>
>> >>Linux-api is already on the Cc list.  Do we need to add more people to
>> >>get some agreements for the syscall?
>> >What kind of agreement are you looking for?  I'd suggest just coding it
>> >up and posting the patches.  Adding syscalls really is really pretty
>> >straightforward and isn't much code at all.
>> >
>> 
>> Sure, I will do that.
>
> Alternatively, would a regular prctl() work here?

Is this something appliation code has to call, or just the dynamic
loader?

prctl in glibc is a variadic function, so if there's a mismatch between
the kernel/userspace syscall convention and the userspace calling
convention (for variadic functions) for specific types, it can't be made
to work in a generic way.

The loader can use inline assembly for system calls and does not have
this issue, but applications would be implcated by it.

Thanks,
Florian