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From:   Florian Weimer <fweimer@redhat.com>
To:     Dave Martin <Dave.Martin@arm.com>
Cc:     "Yu\, Yu-cheng" <yu-cheng.yu@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
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        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>
Date:   Thu, 27 Aug 2020 15:18:39 +0200
In-Reply-To: <20200826170841.GX6642@arm.com> (Dave Martin's message of "Wed,
        26 Aug 2020 18:08:42 +0100")
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* 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.

Thanks,
Florian