From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7D199189525 for ; Thu, 12 Sep 2024 08:26:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726129596; cv=none; b=b+IEM6nDACzF4xaSHEXeeS5jfs84TXCbf7edDFQRMgRUlOO90zZU+xoit6eCz8DF9zPctkAWIUiSra9KjOMF/bMweWOMjU9o9TdcPLhFKX9NInqz3iuLRVbie9eygK8egf5V8XWqrxJ6gU4nRf7rG2MCkch5v2IqQoffnuvUdgA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726129596; c=relaxed/simple; bh=o/ln/aXyOD2d1hjJn0jEzWVVubVN3NXyarbBzfDg7GU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fE7zDdzk/vSqV6Sh2QznnecHNOnBbzf2sd2GtjcnwuLERcA3eqc8my4J4A6ybXWu0FjVDZzb7gIYU/POq3PsLVfvcxuEHnrp8ZDeUek0vNGyTCDSbqB8C44lxc4qBHQBCfMiSAtWGAO0OKj0Tp7m1CVkiCUUslXRGQ1tVfFKUaE= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=tYPBDwtJq5PRjiiuznjlqN4YGJ3mLm2BTFXXKo62NEYgyHVhsvhg6fGSN1qTiuJfT assCNF3DvlxkEF+uZ0h8nB+qyzWjvsokMDIL4H6oMqlvJZkN2LcbCOgxCr6iY6nZdA uDkn6uTCwUX7Sm3GkaAD6m+/rxDwJq+LcBG2eU9llR7MDK1cGIz5/AzsfKvi7zRLHF 84kl3EmFbvi89IzYpEHYqDnMutokN8QFBNyaGOZeb6ueVsGe2wrIXpJAhWyym8aWaI qWPtg7X97PzBybntI0nz/X7Z68LbYXMht2pU2acmuUkfI/1NsbQNz4HdFL/3232tlw 8JOqtHCx0l83A== Message-ID: Date: Thu, 12 Sep 2024 01:25:55 -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: [PATCH v1 1/1] x86/fred: Clear the WFE bit in missing-ENDBRANCH #CP To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, andrew.cooper3@citrix.com References: <20240911231929.2632698-1-xin@zytor.com> <20240912075714.GT4723@noisy.programming.kicks-ass.net> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <20240912075714.GT4723@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/12/2024 12:57 AM, Peter Zijlstra wrote: > On Wed, Sep 11, 2024 at 04:19:29PM -0700, Xin Li (Intel) wrote: > >> +static void ibt_clear_fred_wfe(struct pt_regs *regs) >> +{ >> + if (cpu_feature_enabled(X86_FEATURE_FRED)) >> + regs->fred_cs.wfe = 0; >> +} >> + >> static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) >> { >> if ((error_code & CP_EC) != CP_ENDBR) { >> @@ -90,6 +107,7 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) >> >> if (unlikely(regs->ip == (unsigned long)&ibt_selftest_noendbr)) { >> regs->ax = 0; >> + ibt_clear_fred_wfe(regs); >> return; >> } >> >> @@ -97,6 +115,7 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) >> if (!ibt_fatal) { >> printk(KERN_DEFAULT CUT_HERE); >> __warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL); >> + ibt_clear_fred_wfe(regs); >> return; >> } >> BUG(); > > So, why not clear the bit the moment we know this is CP_ENDBR? > > In the fatal case, we'll hit that BUG and die anyway, nobody cares about > the tracker state in that case. I did think about it, but preferred to leave it as in BUG(). But as you have asked, will change unless someone else disagrees with a good reason :) > > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > index d2c732a34e5d..fde4bdd25a73 100644 > --- a/arch/x86/kernel/cet.c > +++ b/arch/x86/kernel/cet.c > @@ -88,6 +88,8 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code) > return; > } > > + ibt_clear_fred_wfe(regs); > + > if (unlikely(regs->ip == (unsigned long)&ibt_selftest_noendbr)) { > regs->ax = 0; > return; >