From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227WxfON1iNj2M0hMuUc4Fm44cMryJOrvRf9TNfcBxSdFuijbBtdL38c6x45aFpjxE1Cnl0g ARC-Seal: i=1; a=rsa-sha256; t=1516723999; cv=none; d=google.com; s=arc-20160816; b=R0WMbfhOYMmITryDDgmYf549PQmVwl6BFh/h4W2trVXRvVwyI2l/sD7JjnGx0rw+dg c6ohSqG0FUNwqNZwEk6FlIxz9q6jNEI+5DkjQTQWWazEouWnmPupvV1p7iZQhXn6XiyX pZLwUwRxo8UGKvtVWNGUtt2B6PSs8+2oTq268Xt00NWt0XZpIik0gaQ/BEgWcuF7M9+h phhah8hilqhNspudVTCv2zsUGvRHg4q0+qbE4fPYTkXd52bhYcDHknxl6JtxoF8eUpPw QD6yBiV3/bEVf3H3N8+7yLTrgtHzKnkB8yUKvYeW99bKkjAysrIgje4N3rynn2/ivqpQ uA2g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=spamdiagnosticmetadata:spamdiagnosticoutput :content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :dkim-signature:arc-authentication-results; bh=C3EgWFFzzehnPJBo76QRVUP7YX8L5+W37EKr5OmcD0A=; b=jf2hw9fQATLEGuZWHudgqnXQ51k29iauOFc+4v/Vu3pfWDTOKKnVxPZFnkUao85cJ6 HZpEoNa8vo+anWe3VlFKaCGBQLnfqTIfqEWl1uVaty008cwrQnODAynSdxdfmROsEoJQ fAaEF9Ngl/dZxcXvePW3HKTwtNVljWosokmiglgQm0pL2BWSBtkzpiyB6PivaOLtyy76 fT3qc1LAecNXAS3kK7OSn5Wwvv99EcvHFjB8Tm0okEoGV9QS+JkqARm+Qzl7nZd3J6gr LKZcD9XUaZFktLI06lPxjkTrDMf/Un7AoDGMLaRs+z4SKpl9TCB0W2u9UA0E8hFQXSO1 VjSQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@amdcloud.onmicrosoft.com header.s=selector1-amd-com header.b=PImIkjtn; spf=neutral (google.com: 104.47.33.59 is neither permitted nor denied by best guess record for domain of thomas.lendacky@amd.com) smtp.mailfrom=Thomas.Lendacky@amd.com Authentication-Results: mx.google.com; dkim=pass header.i=@amdcloud.onmicrosoft.com header.s=selector1-amd-com header.b=PImIkjtn; spf=neutral (google.com: 104.47.33.59 is neither permitted nor denied by best guess record for domain of thomas.lendacky@amd.com) smtp.mailfrom=Thomas.Lendacky@amd.com Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation To: Andy Lutomirski , KarimAllah Ahmed Cc: linux-kernel@vger.kernel.org, Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Arjan van de Ven , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , David Woodhouse , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Linus Torvalds , Masami Hiramatsu , Paolo Bonzini , Peter Zijlstra , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Tim Chen , kvm@vger.kernel.org, x86@kernel.org, Arjan Van De Ven References: <1516476182-5153-1-git-send-email-karahmed@amazon.de> <1516476182-5153-10-git-send-email-karahmed@amazon.de> <243BE571-AF73-44B3-8D17-193F9E07686A@amacapital.net> From: Tom Lendacky Message-ID: <4e01a7a9-29e4-adcc-3f53-550fb7f3d370@amd.com> Date: Tue, 23 Jan 2018 10:12:48 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <243BE571-AF73-44B3-8D17-193F9E07686A@amacapital.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [165.204.78.1] X-ClientProxiedBy: CO1PR15CA0052.namprd15.prod.outlook.com (10.175.176.20) To DM5PR12MB1146.namprd12.prod.outlook.com (10.168.236.141) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 443fc1e6-7434-4e6a-0197-08d5627c3651 X-MS-Office365-Filtering-HT: Tenant X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(4534165)(4627221)(201703031133081)(201702281549075)(5600026)(4604075)(48565401081)(2017052603307)(7153060)(7193020);SRVR:DM5PR12MB1146; 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A trip back to >> user-space after *restricting* speculation would still affect the BTB. >> >> Quoting from a commit by Tim Chen: >> >> """ >> If IBRS is set, near returns and near indirect jumps/calls will not allow >> their predicted target address to be controlled by code that executed in a >> less privileged prediction mode *BEFORE* the IBRS mode was last written with >> a value of 1 or on another logical processor so long as all Return Stack >> Buffer (RSB) entries from the previous less privileged prediction mode are >> overwritten. >> >> Thus a near indirect jump/call/return may be affected by code in a less >> privileged prediction mode that executed *AFTER* IBRS mode was last written >> with a value of 1. >> """ >> >> [ tglx: Changed macro names and rewrote changelog ] >> [ karahmed: changed macro names *again* and rewrote changelog ] >> >> Signed-off-by: Tim Chen >> Signed-off-by: Thomas Gleixner >> Signed-off-by: KarimAllah Ahmed >> Cc: Andrea Arcangeli >> Cc: Andi Kleen >> Cc: Peter Zijlstra >> Cc: Greg KH >> Cc: Dave Hansen >> Cc: Andy Lutomirski >> Cc: Paolo Bonzini >> Cc: Dan Williams >> Cc: Arjan Van De Ven >> Cc: Linus Torvalds >> Cc: David Woodhouse >> Cc: Ashok Raj >> Link: https://lkml.kernel.org/r/3aab341725ee6a9aafd3141387453b45d788d61a.1515542293.git.tim.c.chen@linux.intel.com >> Signed-off-by: David Woodhouse >> --- >> arch/x86/entry/calling.h | 73 ++++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 73 insertions(+) >> >> diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h >> index 3f48f69..5aafb51 100644 >> --- a/arch/x86/entry/calling.h >> +++ b/arch/x86/entry/calling.h >> @@ -6,6 +6,8 @@ >> #include >> #include >> #include >> +#include >> +#include >> >> /* >> >> @@ -349,3 +351,74 @@ For 32-bit we have the following conventions - kernel is built with >> .Lafter_call_\@: >> #endif >> .endm >> + >> +/* >> + * IBRS related macros >> + */ >> +.macro PUSH_MSR_REGS >> + pushq %rax >> + pushq %rcx >> + pushq %rdx >> +.endm >> + >> +.macro POP_MSR_REGS >> + popq %rdx >> + popq %rcx >> + popq %rax >> +.endm >> + >> +.macro WRMSR_ASM msr_nr:req edx_val:req eax_val:req >> + movl \msr_nr, %ecx >> + movl \edx_val, %edx >> + movl \eax_val, %eax >> + wrmsr >> +.endm >> + >> +.macro RESTRICT_IB_SPEC >> + ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_IBRS >> + PUSH_MSR_REGS >> + WRMSR_ASM $MSR_IA32_SPEC_CTRL, $0, $SPEC_CTRL_IBRS >> + POP_MSR_REGS >> +.Lskip_\@: >> +.endm >> + >> +.macro UNRESTRICT_IB_SPEC >> + ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_IBRS >> + PUSH_MSR_REGS >> + WRMSR_ASM $MSR_IA32_SPEC_CTRL, $0, $0 > > I think you should be writing 2, not 0, since I'm reasonably confident that we want STIBP on. Can you explain why you're writing 0? Do we want to talk about STIBP in general? Should it be (yet another) boot option to enable or disable? If there is STIBP support without IBRS support, it could be a set and forget at boot time. Thanks, Tom > > Also, holy cow, there are so many macros here. > > And a meta question: why are there so many submitters of the same series? >