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Date:   Fri, 2 Dec 2022 18:28:08 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
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        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Peter Zijlstra <peterz@infradead.org>,
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        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
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        dethoma@microsoft.com, akpm@linux-foundation.org,
        Andrew.Cooper3@citrix.com, christina.schimpe@intel.com,
        Yu-cheng Yu <yu-cheng.yu@intel.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [PATCH v4 07/39] x86: Add user control-protection fault handler
Message-ID: <202212021827.03F637C9C9@keescook>
References: <20221203003606.6838-1-rick.p.edgecombe@intel.com>
 <20221203003606.6838-8-rick.p.edgecombe@intel.com>
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In-Reply-To: <20221203003606.6838-8-rick.p.edgecombe@intel.com>
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On Fri, Dec 02, 2022 at 04:35:34PM -0800, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
> 
> A control-protection fault is triggered when a control-flow transfer
> attempt violates Shadow Stack or Indirect Branch Tracking constraints.
> For example, the return address for a RET instruction differs from the copy
> on the shadow stack.
> 
> There already exists a control-protection fault handler for handling kernel
> IBT. Refactor this fault handler into sparate user and kernel handlers,
> like the page fault handler. Add a control-protection handler for usermode.
> 
> Keep the same behavior for the kernel side of the fault handler, except for
> converting a BUG to a WARN in the case of a #CP happening when
> !cpu_feature_enabled(). This unifies the behavior with the new shadow stack
> code, and also prevents the kernel from crashing under this situation which
> is potentially recoverable.
> 
> The control-protection fault handler works in a similar way as the general
> protection fault handler. It provides the si_code SEGV_CPERR to the signal
> handler.
> 
> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> Tested-by: John Allen <john.allen@amd.com>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

This looks nice cleaner to me. Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook