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AJvYcCVmAKvAJAUV+PHiwGy/rRJr1C0uMdRiLHsrAmdtCmPlWQIMWKD+fE17DVMWNtLqN0NAo+86Ct6/zXjKNZs=@vger.kernel.org X-Gm-Message-State: AOJu0YwikyblAz7GZ0XhD2NQ6/hVpeTm+mntrmDwYStJQxTSB7sAYCIr 06jr8RzNc+JpgfjxO0qIZMGjEXorrB43McmzVa1ZxNncjgb5C6j2ck8lW4mbXctFLrMDQpaZr87 3sg== X-Google-Smtp-Source: AGHT+IH0yGN/QwJj2qp5uqOKGauUQieE3T8AzQn7D6+8pBhJNJGOpa+Ovr7omqAZIvsz9KNZ4usYPH1yyCs= X-Received: from pfbbv12.prod.google.com ([2002:a05:6a00:414c:b0:724:f17d:ebd7]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:448a:b0:725:ebab:bb2e with SMTP id d2e1a72fcca58-72daf981283mr35774059b3a.11.1737649519289; Thu, 23 Jan 2025 08:25:19 -0800 (PST) Date: Thu, 23 Jan 2025 08:25:17 -0800 In-Reply-To: <20250118152655.GBZ4vIP44MivU2Bv0i@fat_crate.local> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241216173142.GDZ2Bj_uPBG3TTPYd_@fat_crate.local> <20241230111456.GBZ3KAsLTrVs77UmxL@fat_crate.local> <20250108154901.GFZ36ebXAZMFZJ7D8t@fat_crate.local> <20250108181434.GGZ37AiioQkcYbqugO@fat_crate.local> <20250111125215.GAZ4Jpf6tbcoS7jCzz@fat_crate.local> <20250118152655.GBZ4vIP44MivU2Bv0i@fat_crate.local> Message-ID: Subject: Re: [PATCH] x86/bugs: KVM: Add support for SRSO_MSR_FIX From: Sean Christopherson To: Borislav Petkov Cc: Borislav Petkov , X86 ML , Paolo Bonzini , Josh Poimboeuf , Pawan Gupta , KVM , LKML Content-Type: text/plain; charset="us-ascii" On Sat, Jan 18, 2025, Borislav Petkov wrote: > static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_NONE; > @@ -2663,6 +2665,12 @@ static void __init srso_select_mitigation(void) Unless I'm missing something, the cpu_mitigations_off() and "srso_cmd == SRSO_CMD_OFF" cases need to clear the feature diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 9e3ea7f1b3587..3939a8dee27d4 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2581,6 +2581,7 @@ static void __init srso_select_mitigation(void) srso_cmd == SRSO_CMD_OFF) { if (boot_cpu_has(X86_FEATURE_SBPB)) x86_pred_cmd = PRED_CMD_SBPB; + setup_clear_cpu_cap(X86_FEATURE_SRSO_BP_SPEC_REDUCE); return; } There's also the Zen1/Zen2 ucode+!SMT path, which I assume is irreveleant in practice: if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) { setup_force_cpu_cap(X86_FEATURE_SRSO_NO); return; } But if we wanted to catch all paths, wrap the guts and clear the feature in the outer layer? diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 9e3ea7f1b3587..0501e31971421 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2572,7 +2572,7 @@ early_param("spec_rstack_overflow", srso_parse_cmdline); #define SRSO_NOTICE "WARNING: See https://kernel.org/doc/html/latest/admin-guide/hw-vuln/srso.html for mitigation options." -static void __init srso_select_mitigation(void) +static void __init __srso_select_mitigation(void) { bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE); @@ -2692,11 +2692,15 @@ static void __init srso_select_mitigation(void) } out: + pr_info("%s\n", srso_strings[srso_mitigation]); +} + +static void __init srso_select_mitigation(void) +{ + __srso_select_mitigation(); if (srso_mitigation != SRSO_MITIGATION_BP_SPEC_REDUCE) setup_clear_cpu_cap(X86_FEATURE_SRSO_BP_SPEC_REDUCE); - - pr_info("%s\n", srso_strings[srso_mitigation]); } #undef pr_fmt > ibpb_on_vmexit: > case SRSO_CMD_IBPB_ON_VMEXIT: > + if (boot_cpu_has(X86_FEATURE_SRSO_BP_SPEC_REDUCE)) { > + pr_notice("Reducing speculation to address VM/HV SRSO attack vector.\n"); > + srso_mitigation = 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); > @@ -2684,6 +2692,10 @@ static void __init srso_select_mitigation(void) > } > > out: > + Spurious newlines. > + if (srso_mitigation != SRSO_MITIGATION_BP_SPEC_REDUCE) > + setup_clear_cpu_cap(X86_FEATURE_SRSO_BP_SPEC_REDUCE); > + > pr_info("%s\n", srso_strings[srso_mitigation]); > }