From: David Kaplan Date: Fri, 18 Apr 2025 16:17:07 +0000 (-0500) Subject: x86/bugs: Restructure TAA mitigation X-Git-Tag: v6.16-rc1~195^2~31^2~14 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bdd7fce7a8168cebd400926d6352d2fbc1ac9f79;p=thirdparty%2Fkernel%2Flinux.git x86/bugs: Restructure TAA mitigation Restructure TAA mitigation to use select/update/apply functions to create consistent vulnerability handling. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/20250418161721.1855190-3-david.kaplan@amd.com --- diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index f697e6b41afd3..5db21d2ee87dd 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -65,6 +65,8 @@ static void __init mds_apply_mitigation(void); static void __init md_clear_update_mitigation(void); static void __init md_clear_select_mitigation(void); static void __init taa_select_mitigation(void); +static void __init taa_update_mitigation(void); +static void __init taa_apply_mitigation(void); static void __init mmio_select_mitigation(void); static void __init srbds_select_mitigation(void); static void __init l1d_flush_select_mitigation(void); @@ -194,6 +196,7 @@ void __init cpu_select_mitigations(void) ssb_select_mitigation(); l1tf_select_mitigation(); mds_select_mitigation(); + taa_select_mitigation(); md_clear_select_mitigation(); srbds_select_mitigation(); l1d_flush_select_mitigation(); @@ -210,8 +213,10 @@ void __init cpu_select_mitigations(void) * choices. */ mds_update_mitigation(); + taa_update_mitigation(); mds_apply_mitigation(); + taa_apply_mitigation(); } /* @@ -397,6 +402,11 @@ static const char * const taa_strings[] = { [TAA_MITIGATION_TSX_DISABLED] = "Mitigation: TSX disabled", }; +static bool __init taa_vulnerable(void) +{ + return boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM); +} + static void __init taa_select_mitigation(void) { if (!boot_cpu_has_bug(X86_BUG_TAA)) { @@ -410,48 +420,63 @@ static void __init taa_select_mitigation(void) return; } - if (cpu_mitigations_off()) { + if (cpu_mitigations_off()) taa_mitigation = TAA_MITIGATION_OFF; - return; - } - /* - * TAA mitigation via VERW is turned off if both - * tsx_async_abort=off and mds=off are specified. - */ - if (taa_mitigation == TAA_MITIGATION_OFF && - mds_mitigation == MDS_MITIGATION_OFF) + /* Microcode will be checked in taa_update_mitigation(). */ + if (taa_mitigation == TAA_MITIGATION_AUTO) + taa_mitigation = TAA_MITIGATION_VERW; + + if (taa_mitigation != TAA_MITIGATION_OFF) + verw_clear_cpu_buf_mitigation_selected = true; +} + +static void __init taa_update_mitigation(void) +{ + if (!taa_vulnerable() || cpu_mitigations_off()) return; - if (boot_cpu_has(X86_FEATURE_MD_CLEAR)) + if (verw_clear_cpu_buf_mitigation_selected) taa_mitigation = TAA_MITIGATION_VERW; - else - taa_mitigation = TAA_MITIGATION_UCODE_NEEDED; - /* - * VERW doesn't clear the CPU buffers when MD_CLEAR=1 and MDS_NO=1. - * A microcode update fixes this behavior to clear CPU buffers. It also - * adds support for MSR_IA32_TSX_CTRL which is enumerated by the - * ARCH_CAP_TSX_CTRL_MSR bit. - * - * On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode - * update is required. - */ - if ( (x86_arch_cap_msr & ARCH_CAP_MDS_NO) && - !(x86_arch_cap_msr & ARCH_CAP_TSX_CTRL_MSR)) - taa_mitigation = TAA_MITIGATION_UCODE_NEEDED; + if (taa_mitigation == TAA_MITIGATION_VERW) { + /* Check if the requisite ucode is available. */ + if (!boot_cpu_has(X86_FEATURE_MD_CLEAR)) + taa_mitigation = TAA_MITIGATION_UCODE_NEEDED; - /* - * TSX is enabled, select alternate mitigation for TAA which is - * the same as MDS. Enable MDS static branch to clear CPU buffers. - * - * For guests that can't determine whether the correct microcode is - * present on host, enable the mitigation for UCODE_NEEDED as well. - */ - setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF); + /* + * VERW doesn't clear the CPU buffers when MD_CLEAR=1 and MDS_NO=1. + * A microcode update fixes this behavior to clear CPU buffers. It also + * adds support for MSR_IA32_TSX_CTRL which is enumerated by the + * ARCH_CAP_TSX_CTRL_MSR bit. + * + * On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode + * update is required. + */ + if ((x86_arch_cap_msr & ARCH_CAP_MDS_NO) && + !(x86_arch_cap_msr & ARCH_CAP_TSX_CTRL_MSR)) + taa_mitigation = TAA_MITIGATION_UCODE_NEEDED; + } - if (taa_nosmt || cpu_mitigations_auto_nosmt()) - cpu_smt_disable(false); + pr_info("%s\n", taa_strings[taa_mitigation]); +} + +static void __init taa_apply_mitigation(void) +{ + if (taa_mitigation == TAA_MITIGATION_VERW || + taa_mitigation == TAA_MITIGATION_UCODE_NEEDED) { + /* + * TSX is enabled, select alternate mitigation for TAA which is + * the same as MDS. Enable MDS static branch to clear CPU buffers. + * + * For guests that can't determine whether the correct microcode is + * present on host, enable the mitigation for UCODE_NEEDED as well. + */ + setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF); + + if (taa_nosmt || cpu_mitigations_auto_nosmt()) + cpu_smt_disable(false); + } } static int __init tsx_async_abort_parse_cmdline(char *str) @@ -660,7 +685,6 @@ out: static void __init md_clear_select_mitigation(void) { - taa_select_mitigation(); mmio_select_mitigation(); rfds_select_mitigation();