linux-kernel - Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrXnzOwLSHWOtKTLuybCTZ=w+cBVMhs2uCzd+LSdbijQ3g@mail.gmail.com>
Date:   Thu, 3 Sep 2020 09:25:51 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Cc:     Dave Hansen <dave.hansen@...el.com>, Jann Horn <jannh@...gle.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        kernel list <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>,
        Andy Lutomirski <luto@...nel.org>,
        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>, 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>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>
Subject: Re: [PATCH v11 6/9] x86/cet: Add PTRACE interface for CET

On Thu, Sep 3, 2020 at 9:21 AM Yu, Yu-cheng <yu-cheng.yu@...el.com> wrote:
>
> On 9/3/2020 9:11 AM, Dave Hansen wrote:
> > On 9/3/20 9:09 AM, Yu, Yu-cheng wrote:
> >> If the debugger is going to write an MSR, only in the third case would
> >> this make a slight sense.  For example, if the system has CET enabled,
> >> but the task does not have CET enabled, and GDB is writing to a CET MSR.
> >>   But still, this is strange to me.
> >
> > If this is strange, then why do we even _implement_ writes?
> >
>
> For example, if the task has CET enabled, and it is in a control
> protection fault, the debugger can clear the task's IBT state, or unwind
> the shadow stack, etc.  But if the task does not have CET enabled (its
> CET MSRs are in INIT state), it would make sense for the PTRACE call to
> return failure than doing something else, right?

What do you mean "something else"?  I assume that, if GDB tells
ptrace() to write some value to the CET MSR, then it should get that
value.  If GDB writes to it on a task that is not currently using CET,
I don't see why it should fail.

--Andy