From: Dave Hansen <dave.hansen@intel.com>
To: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org
Cc: linux-tip-commits@vger.kernel.org,
Nikunj A Dadhania <nikunj@amd.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Borislav Petkov (AMD)" <bp@alien8.de>,
Sohil Mehta <sohil.mehta@intel.com>,
stable@vger.kernel.org, #@tip-bot2.tec.linutronix.de,
6.9+@tip-bot2.tec.linutronix.de, x86@kernel.org
Subject: Re: [tip: x86/urgent] x86/cpu: Disable CR pinning during CPU bringup
Date: Wed, 18 Mar 2026 14:30:13 -0700 [thread overview]
Message-ID: <ea53e6a9-4f8a-49a8-95ea-40d2f667dc7f@intel.com> (raw)
In-Reply-To: <20260318210950.GC3739106@noisy.programming.kicks-ass.net>
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.
next prev parent reply other threads:[~2026-03-18 21:30 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20260318075654.1792916-3-nikunj@amd.com>
2026-03-18 18:51 ` [tip: x86/urgent] x86/cpu: Disable CR pinning during CPU bringup tip-bot2 for Dave Hansen
2026-03-18 20:47 ` Peter Zijlstra
2026-03-18 21:08 ` Borislav Petkov
2026-03-18 21:30 ` Peter Zijlstra
2026-03-18 22:01 ` Borislav Petkov
2026-03-18 21:09 ` Peter Zijlstra
2026-03-18 21:30 ` Dave Hansen [this message]
2026-03-18 22:09 ` Peter Zijlstra
2026-03-20 9:25 ` [PATCH] x86/cpu: Add comment clarifying CRn pinning Peter Zijlstra
2026-03-20 11:34 ` Borislav Petkov
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