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From:   Florian Weimer <fweimer@redhat.com>
To:     "H.J. Lu" <hjl.tools@gmail.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>,
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        Ingo Molnar <mingo@redhat.com>,
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        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>,
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        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
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        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
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        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Weijiang Yang <weijiang.yang@intel.com>
Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack
References: <20200825002540.3351-1-yu-cheng.yu@intel.com>
        <20200825002540.3351-26-yu-cheng.yu@intel.com>
        <CALCETrVpLnZGfWWLpJO+aZ9aBbx5KGaCskejXiCXF1GtsFFoPg@mail.gmail.com>
        <2d253891-9393-44d0-35e0-4b9a2da23cec@intel.com>
        <086c73d8-9b06-f074-e315-9964eb666db9@intel.com>
        <73c2211f-8811-2d9f-1930-1c5035e6129c@intel.com>
        <af258a0e-56e9-3747-f765-dfe45ce76bba@intel.com>
        <ef7f9e24-f952-d78c-373e-85435f742688@intel.com>
        <20200826164604.GW6642@arm.com>
        <87ft892vvf.fsf@oldenburg2.str.redhat.com>
        <20200826170841.GX6642@arm.com>
        <87tuwow7kg.fsf@oldenburg2.str.redhat.com>
        <CAMe9rOrhjLSaMNABnzd=Kp5UeVot1Qkx0_PnMng=sT+wd9Xubw@mail.gmail.com>
Date:   Thu, 27 Aug 2020 15:36:28 +0200
In-Reply-To: <CAMe9rOrhjLSaMNABnzd=Kp5UeVot1Qkx0_PnMng=sT+wd9Xubw@mail.gmail.com>
        (H. J. Lu's message of "Thu, 27 Aug 2020 06:28:56 -0700")
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* 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).

Thanks,
Florian