From nobody Sun Nov 24 16:29:49 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C32B120ED; Mon, 4 Nov 2024 10:15:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730715348; cv=none; b=V1gRVtfWoBL1AZ0rYaS34UxOL7a/k5T7d4dYs0AVSPE9Urtyv5DWFvXYDgOljfuSC/Xqv3rWPElDatvKrmOss9GBDwGSL+jpvRdmjIAixZApqRcnIcOPHzYprMdDtSyERxuWtMXqVXCYQ4V8F6xw8Nz3mVmTPmtsW/O+HBkA9Vc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730715348; c=relaxed/simple; bh=InWUU3D2Dk79W7Gl9bItAteAnFGljFzsGKpkdweMKHY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=qLBSSlDiOgkAjzE0pvqaakKwZ/Mf1EEV8jbksaLUbhxyka+o3/uAxoex2jqDhWe8DXRunT+DSuigh5fbky4Ss0xwXeGaiYz4fTGwmXls/xwQS5MDpNO9ubMmBYu6a5Y17RgzvRc/6cEAam5ATo1wh17cKOKPMzvkV6vQ0BqS1Tc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EHFm9Fly; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EHFm9Fly" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA24CC4CECE; Mon, 4 Nov 2024 10:15:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730715348; bh=InWUU3D2Dk79W7Gl9bItAteAnFGljFzsGKpkdweMKHY=; h=From:To:Cc:Subject:Date:From; b=EHFm9FlyAD2DFhNZT2J0RbMcZoapYZ2+aOcmOxGsdi67+47XT64Qi+Av8s7/MzsE+ F4Z/WUczB7PISowE3ja8a83AFgLl/q1gGnL1cD5+Len9SQY3VrsxeT93jL6n8RhlUi 4BzhV4nhkeR5LExaV8M17SbLJW8OfUnHBnPwBotvZn9N2CBLppQVz5c8beqzyZe/n5 cjw1xtsmne12YIdNpcrog7cdF8eIEzbdnRBhRKt4bLP3mEcqMUEFNjIM2A10TUaSrE hVmzFsDbiPLBnjHR5NkU3hDLCl0ssFDEGREA6N1v+n/ZpJzsr9uOt+TuKUDEpGygI4 68xVBJ5GfeFgQ== From: Borislav Petkov To: X86 ML Cc: Josh Poimboeuf , Pawan Gupta , kvm@vger.kernel.org, LKML , "Borislav Petkov (AMD)" Subject: [PATCH] x86/bugs: Adjust SRSO mitigation to new features Date: Mon, 4 Nov 2024 11:15:43 +0100 Message-ID: <20241104101543.31885-1-bp@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Borislav Petkov (AMD)" If the machine has: CPUID Fn8000_0021_EAX[30] (SRSO_USER_KERNEL_NO) -- If this bit is 1, it indicates the CPU is not subject to the SRSO vulnerability across user/kernel boundaries. have it fall back to IBPB on VMEXIT only, in the case it is going to run VMs: Speculative Return Stack Overflow: CPU user/kernel transitions protected,= falling back to IBPB-on-VMEXIT Speculative Return Stack Overflow: Mitigation: IBPB on VMEXIT only Then, upon KVM module load and in case the machine has CPUID Fn8000_0021_EAX[31] (SRSO_MSR_FIX). If this bit is 1, it indicates that software may use MSR BP_CFG[BpSpecReduce] to mitigate SRSO. enable this BpSpecReduce bit to mitigate SRSO across guest/host boundaries. Signed-off-by: Borislav Petkov (AMD) --- arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/include/asm/msr-index.h | 1 + arch/x86/kernel/cpu/bugs.c | 16 +++++++++++++++- arch/x86/kernel/cpu/common.c | 1 + arch/x86/kvm/cpuid.c | 1 + arch/x86/kvm/svm/svm.c | 6 ++++++ arch/x86/lib/msr.c | 2 ++ 7 files changed, 28 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpuf= eatures.h index 924f530129d7..9d71f06e09a4 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -462,6 +462,8 @@ #define X86_FEATURE_SBPB (20*32+27) /* Selective Branch Prediction Barrie= r */ #define X86_FEATURE_IBPB_BRTYPE (20*32+28) /* MSR_PRED_CMD[IBPB] flushes = all branch type predictions */ #define X86_FEATURE_SRSO_NO (20*32+29) /* CPU is not affected by SRSO */ +#define X86_FEATURE_SRSO_USER_KERNEL_NO (20*32+30) /* CPU is not affected = by SRSO across user/kernel boundaries */ +#define X86_FEATURE_SRSO_MSR_FIX (20*32+31) /* MSR BP_CFG[BpSpecReduce] ca= n be used to mitigate SRSO */ =20 /* * Extended auxiliary flags: Linux defined - for features scattered in var= ious diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-in= dex.h index 3ae84c3b8e6d..1372a569fb58 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -717,6 +717,7 @@ =20 /* Zen4 */ #define MSR_ZEN4_BP_CFG 0xc001102e +#define MSR_ZEN4_BP_CFG_BP_SPEC_REDUCE_BIT 4 #define MSR_ZEN4_BP_CFG_SHARED_BTB_FIX_BIT 5 =20 /* Fam 19h MSRs */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 83b34a522dd7..5dffd1e679da 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2536,6 +2536,7 @@ enum srso_mitigation { SRSO_MITIGATION_SAFE_RET, SRSO_MITIGATION_IBPB, SRSO_MITIGATION_IBPB_ON_VMEXIT, + SRSO_MITIGATION_BP_SPEC_REDUCE, }; =20 enum srso_mitigation_cmd { @@ -2553,7 +2554,8 @@ static const char * const srso_strings[] =3D { [SRSO_MITIGATION_MICROCODE] =3D "Vulnerable: Microcode, no safe RET", [SRSO_MITIGATION_SAFE_RET] =3D "Mitigation: Safe RET", [SRSO_MITIGATION_IBPB] =3D "Mitigation: IBPB", - [SRSO_MITIGATION_IBPB_ON_VMEXIT] =3D "Mitigation: IBPB on VMEXIT only" + [SRSO_MITIGATION_IBPB_ON_VMEXIT] =3D "Mitigation: IBPB on VMEXIT only", + [SRSO_MITIGATION_BP_SPEC_REDUCE] =3D "Mitigation: Reduced Speculation" }; =20 static enum srso_mitigation srso_mitigation __ro_after_init =3D SRSO_MITIG= ATION_NONE; @@ -2628,6 +2630,11 @@ static void __init srso_select_mitigation(void) break; =20 case SRSO_CMD_SAFE_RET: + if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO)) { + pr_notice("CPU user/kernel transitions protected, falling back to IBPB-= on-VMEXIT\n"); + goto ibpb_on_vmexit; + } + if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) { /* * Enable the return thunk for generated code @@ -2671,7 +2678,14 @@ static void __init srso_select_mitigation(void) } break; =20 +ibpb_on_vmexit: case SRSO_CMD_IBPB_ON_VMEXIT: + if (boot_cpu_has(X86_FEATURE_SRSO_MSR_FIX)) { + pr_notice("Reducing speculation to address VM/HV SRSO attack vector.\n"= ); + srso_mitigation =3D SRSO_MITIGATION_BP_SPEC_REDUCE; + break; + } + if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) { if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) { setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT); diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 8f41ab219cf1..ca3b588b51aa 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1273,6 +1273,7 @@ static const struct x86_cpu_id cpu_vuln_blacklist[] _= _initconst =3D { VULNBL_AMD(0x17, RETBLEED | SMT_RSB | SRSO), VULNBL_HYGON(0x18, RETBLEED | SMT_RSB | SRSO), VULNBL_AMD(0x19, SRSO), + VULNBL_AMD(0x1a, SRSO), {} }; =20 diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 41786b834b16..d54cd67c8c50 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -799,6 +799,7 @@ void kvm_set_cpu_caps(void) =20 kvm_cpu_cap_check_and_set(X86_FEATURE_SBPB); kvm_cpu_cap_check_and_set(X86_FEATURE_IBPB_BRTYPE); + kvm_cpu_cap_check_and_set(X86_FEATURE_SRSO_USER_KERNEL_NO); kvm_cpu_cap_check_and_set(X86_FEATURE_SRSO_NO); =20 kvm_cpu_cap_init_kvm_defined(CPUID_8000_0022_EAX, diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 9df3e1e5ae81..03f29912a638 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -608,6 +608,9 @@ static void svm_disable_virtualization_cpu(void) kvm_cpu_svm_disable(); =20 amd_pmu_disable_virt(); + + if (cpu_feature_enabled(X86_FEATURE_SRSO_MSR_FIX)) + msr_clear_bit(MSR_ZEN4_BP_CFG, MSR_ZEN4_BP_CFG_BP_SPEC_REDUCE_BIT); } =20 static int svm_enable_virtualization_cpu(void) @@ -685,6 +688,9 @@ static int svm_enable_virtualization_cpu(void) rdmsr(MSR_TSC_AUX, sev_es_host_save_area(sd)->tsc_aux, msr_hi); } =20 + if (cpu_feature_enabled(X86_FEATURE_SRSO_MSR_FIX)) + msr_set_bit(MSR_ZEN4_BP_CFG, MSR_ZEN4_BP_CFG_BP_SPEC_REDUCE_BIT); + return 0; } =20 diff --git a/arch/x86/lib/msr.c b/arch/x86/lib/msr.c index 4bf4fad5b148..5a18ecc04a6c 100644 --- a/arch/x86/lib/msr.c +++ b/arch/x86/lib/msr.c @@ -103,6 +103,7 @@ int msr_set_bit(u32 msr, u8 bit) { return __flip_bit(msr, bit, true); } +EXPORT_SYMBOL_GPL(msr_set_bit); =20 /** * msr_clear_bit - Clear @bit in a MSR @msr. @@ -118,6 +119,7 @@ int msr_clear_bit(u32 msr, u8 bit) { return __flip_bit(msr, bit, false); } +EXPORT_SYMBOL_GPL(msr_clear_bit); =20 #ifdef CONFIG_TRACEPOINTS void do_trace_write_msr(unsigned int msr, u64 val, int failed) --=20 2.43.0