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Date:   Mon, 3 Oct 2022 10:26:50 -0700
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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        Arnd Bergmann <arnd@arndb.de>,
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        "Ravi V . Shankar" <ravi.v.shankar@intel.com>,
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        jamorris@linux.microsoft.com, dethoma@microsoft.com,
        Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: Re: [PATCH v2 03/39] x86/cpufeatures: Add CPU feature flags for
 shadow stacks
Message-ID: <202210031026.22DBF47CCD@keescook>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
 <20220929222936.14584-4-rick.p.edgecombe@intel.com>
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On Thu, Sep 29, 2022 at 03:29:00PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
> 
> The Control-Flow Enforcement Technology contains two related features,
> one of which is Shadow Stacks. Future patches will utilize this feature
> for shadow stack support in KVM, so add a CPU feature flags for Shadow
> Stacks (CPUID.(EAX=7,ECX=0):ECX[bit 7]).
> 
> To protect shadow stack state from malicious modification, the registers
> are only accessible in supervisor mode. This implementation
> context-switches the registers with XSAVES. Make X86_FEATURE_SHSTK depend
> on XSAVES.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

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

-- 
Kees Cook