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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Thu, 27 Aug 2020 07:08:09 -0700
Message-ID: <CAMe9rOpuwZesJqY_2wYhdRXMhd7g0a+MRqPtXKh7wX5B5-OSbA@mail.gmail.com>
Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for
 shadow stack
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Dave Martin <Dave.Martin@arm.com>,
        "Yu, Yu-cheng" <yu-cheng.yu@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
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        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
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        Weijiang Yang <weijiang.yang@intel.com>
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On Thu, Aug 27, 2020 at 7:07 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Aug 27, 2020 at 6:36 AM Florian Weimer <fweimer@redhat.com> wrote:
> >
> > * H. J. Lu:
> >
> > > On Thu, Aug 27, 2020 at 6:19 AM Florian Weimer <fweimer@redhat.com> wrote:
> > >>
> > >> * Dave Martin:
> > >>
> > >> > You're right that this has implications: for i386, libc probably pulls
> > >> > more arguments off the stack than are really there in some situations.
> > >> > This isn't a new problem though.  There are already generic prctls with
> > >> > fewer than 4 args that are used on x86.
> > >>
> > >> As originally posted, glibc prctl would have to know that it has to pull
> > >> an u64 argument off the argument list for ARCH_X86_CET_DISABLE.  But
> > >> then the u64 argument is a problem for arch_prctl as well.
> > >>
> > >
> > > Argument of ARCH_X86_CET_DISABLE is int and passed in register.
> >
> > The commit message and the C source say otherwise, I think (not sure
> > about the C source, not a kernel hacker).
>
> It should read:
>
> arch_prctl(ARCH_X86_CET_DISABLE, unsigned long features)
>

Or

arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features)


-- 
H.J.