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 A1B1EBA3F; Fri, 2 May 2025 05:47:35 +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=1746164858; cv=none; b=dq6+nKnO1k/ON5frBE0WZ+2ob9d6nUxFB2OayTzWBEuUXUuxT5F9SjZW06RPDKz15eUzg8p18bi2NFOxP4fu6IhWJYXMfs7ybDldQuTtWjBnuV8oxNbhnsm87EZZY3ToTjOwM8A5bk7SrWfL1qk/v+FMGRWY3p4f1TrCZaOGwE8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746164858; c=relaxed/simple; bh=CRlm8DglgsjDBM3aRfMpTQ7akikLGNAa4uzuEFyxihU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WhreWaRz97+Utjfse6yzwNrIqv72g9T1M3gvU15ZDibMGGjrTa28SULnO3r/n/7m2M8YmBtbrWAC+KFZ22b3Xz88mu/bsIaniVy9vFYfJdupLSn60xRURoKidTcQ5StnkmFmkngzntHcuy1avT83y1QLIqd1G4RlKWI2Vz/w0ac= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=R4OZ87Vt; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="R4OZ87Vt" Received: from [192.168.7.202] ([71.202.166.45]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 5425kkje1780668 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Thu, 1 May 2025 22:46:47 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 5425kkje1780668 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025042001; t=1746164809; bh=MGfso3qvTctMT+qsQxGakZO6pbzlMRbsUmiKDI86FZ0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=R4OZ87Vtppt5v9J2EdCzFLGVKWqP9EyshJYqWkW/qTgZnPrKpAhmgz8UT6Lojiu5l 3QxrJYjGaM6aeq1eXQl6//Q5LykfWO5JlHATefd0jJ3v3VKCPJg+MIR68f3r6FpFxK 8EIKOQe66SNOYTTakLEaSq1FAWyDFKx+7iRJKmpNvkKCckyVnN9JkgFVdRZaBePpUX G3GLZWcf3mlcEh3Jo/PBnU7abFTYXnU6q9bRCny3G16L20vDzM7u5tQ2mA/xjHPwXP t6yVIaio1jQGUu4AErWBVEVJjIujrXCOMnr4hHudfxLoqaUxld7T63lIdgwLtHTD7s IKsiUxtRR1dXQ== Message-ID: <5e9bfa4b-4440-4d7b-895c-03a3358d4ae6@zytor.com> Date: Thu, 1 May 2025 22:46:45 -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 v2 00/13] objtool: Detect and warn about indirect calls in __nocfi functions To: Sean Christopherson , Peter Zijlstra Cc: "H. Peter Anvin" , x86@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, pbonzini@redhat.com, ardb@kernel.org, kees@kernel.org, Arnd Bergmann , gregkh@linuxfoundation.org, jpoimboe@kernel.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-efi@vger.kernel.org, samitolvanen@google.com, ojeda@kernel.org References: <20250430110734.392235199@infradead.org> <8B86A3AE-A296-438C-A7A7-F844C66D0198@zytor.com> <20250430190600.GQ4439@noisy.programming.kicks-ass.net> <20250501103038.GB4356@noisy.programming.kicks-ass.net> <20250501153844.GD4356@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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >> Something like so... except this is broken. Its reporting spurious >> interrupts on vector 0x00, so something is buggered passing that vector >> along. I'm a bit late to the party :) Peter kind of got what I had in the FRED patch set v8 or earlier: https://lore.kernel.org/lkml/20230410081438.1750-34-xin3.li@intel.com/ > Uh, aren't you making this way more complex than it needs to be? IIUC, KVM never > uses the FRED hardware entry points, i.e. the FRED entry tables don't need to be > in place because they'll never be used. The only bits of code KVM needs is the > __fred_entry_from_kvm() glue. +1 > > Lightly tested, but this combo works for IRQs and NMIs on non-FRED hardware. > > -- > From 664468143109ab7c525c0babeba62195fa4c657e Mon Sep 17 00:00:00 2001 > From: Sean Christopherson > Date: Thu, 1 May 2025 11:20:29 -0700 > Subject: [PATCH 1/2] x86/fred: Play nice with invoking > asm_fred_entry_from_kvm() on non-FRED hardware > > Modify asm_fred_entry_from_kvm() to allow it to be invoked by KVM even > when FRED isn't fully enabled, e.g. when running with CONFIG_X86_FRED=y > on non-FRED hardware. This will allow forcing KVM to always use the FRED > entry points for 64-bit kernels, which in turn will eliminate a rather > gross non-CFI indirect call that KVM uses to trampoline IRQs by doing IDT > lookups. > > When FRED isn't enabled, simply skip ERETS and restore RBP and RSP from > the stack frame prior to doing a "regular" RET back to KVM (in quotes > because of all the RET mitigation horrors). > > Signed-off-by: Sean Christopherson > --- > arch/x86/entry/entry_64_fred.S | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S > index 29c5c32c16c3..7aff2f0a285f 100644 > --- a/arch/x86/entry/entry_64_fred.S > +++ b/arch/x86/entry/entry_64_fred.S > @@ -116,7 +116,8 @@ SYM_FUNC_START(asm_fred_entry_from_kvm) > movq %rsp, %rdi /* %rdi -> pt_regs */ > call __fred_entry_from_kvm /* Call the C entry point */ > POP_REGS > - ERETS > + > + ALTERNATIVE "", __stringify(ERETS), X86_FEATURE_FRED Neat! I ever had a plan to do this with "sub $0x8,%rsp; iret;" for non-FRED case. But obviously doing nothing here is the best. > 1: > /* > * Objtool doesn't understand what ERETS does, this hint tells it that > @@ -124,7 +125,7 @@ SYM_FUNC_START(asm_fred_entry_from_kvm) > * isn't strictly needed, but it's the simplest form. > */ > UNWIND_HINT_RESTORE > - pop %rbp > + leave This is a smart change. When !X86_FEATURE_FRED, the FRED stack frame set up for ERETS is implicitly skipped by leave. Maybe add a comment to explain LEAVE works for both cases?