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X-CSE-ConnectionGUID: NZaumW1DTtqyN66obKJwbQ== X-CSE-MsgGUID: TEnVqzE2SLuPx25X0tsGMQ== X-IronPort-AV: E=McAfee;i="6800,10657,11733"; a="78796095" X-IronPort-AV: E=Sophos;i="6.23,128,1770624000"; d="scan'208";a="78796095" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2026 14:30:14 -0700 X-CSE-ConnectionGUID: TGssMGK5Qg2KbdCDX9PqUg== X-CSE-MsgGUID: PWtroBiSR+SC8uNhxkofMg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,128,1770624000"; d="scan'208";a="227712366" Received: from unknown (HELO [10.24.81.183]) ([10.24.81.183]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2026 14:30:13 -0700 Message-ID: Date: Wed, 18 Mar 2026 14:30:13 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [tip: x86/urgent] x86/cpu: Disable CR pinning during CPU bringup To: Peter Zijlstra , linux-kernel@vger.kernel.org Cc: linux-tip-commits@vger.kernel.org, Nikunj A Dadhania , Dave Hansen , "Borislav Petkov (AMD)" , Sohil Mehta , stable@vger.kernel.org, #@tip-bot2.tec.linutronix.de, 6.9+@tip-bot2.tec.linutronix.de, x86@kernel.org References: <20260318075654.1792916-3-nikunj@amd.com> <177385987098.1647592.3381141860481415647.tip-bot2@tip-bot2> <20260318204722.GD3738786@noisy.programming.kicks-ass.net> <20260318210950.GC3739106@noisy.programming.kicks-ass.net> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/18/26 14:09, Peter Zijlstra wrote: > So currently we setup an IDT and everything, then setup the FRED MSRs, > flip CR4_FRED and call it a day. But we could just explicitly poison all > the IDT stuff to cause tripple faults. We already have: /* Enable FRED */ cr4_set_bits(X86_CR4_FRED); /* Any further IDT use is a bug */ idt_invalidate(); which I think means that if you clear X86_CR4_FRED, you triple-fault on the next reference to the IDT. That's a fate far worse than having the CR-pinning code silently fix up X86_CR4_FRED. It's arguable that having X86_CR4_FRED pinned in the first place makes things less secure if an attacker is thwacking CR4 bits.