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Subject: Re: [PATCH v28 04/10] x86/cet/ibt: Disable IBT for ia32
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, 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>,
        Florian Weimer <fweimer@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        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>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Haitao Huang <haitao.huang@intel.com>,
        Rick P Edgecombe <rick.p.edgecombe@intel.com>
References: <20210722205723.9476-1-yu-cheng.yu@intel.com>
 <20210722205723.9476-5-yu-cheng.yu@intel.com>
From:   Andy Lutomirski <luto@kernel.org>
Message-ID: <3318ca57-7ac3-8296-f9ae-0ae83d5f95dd@kernel.org>
Date:   Mon, 9 Aug 2021 16:04:18 -0700
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On 7/22/21 1:57 PM, Yu-cheng Yu wrote:
> In a signal, a task's IBT status needs to be saved to the signal frame, and
> later restored in sigreturn.  For the purpose, previous versions of the
> series add a new struct to the signal frame.  However, a new signal frame
> format (or re-using a reserved space) introduces complex compatibility
> issues.
> 
> In the discussion (see link below), Andy Lutomirski proposed using a
> ucontext flag.  The approach is clean and eliminates most compatibility
> issues.
> 
> However, a legacy IA32 signal frame does not have ucontext and cannot
> support a uc flag.  Thus,
> 
> - Disable IBT for ia32.
> - In ia32 sigreturn, verify ibt is disabled.

Acked-by: Andy Lutomirski <luto@kernel.org>