From: David Kaplan Date: Mon, 7 Jul 2025 18:32:57 +0000 (-0500) Subject: cpu: Define attack vectors X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=19c24f7ee39af503b9731067b91add627b70ecb6;p=users%2Fjedix%2Flinux-maple.git cpu: Define attack vectors Define 4 new attack vectors that are used for controlling CPU speculation mitigations. These may be individually disabled as part of the mitigations= command line. Attack vector controls are combined with global options like 'auto' or 'auto,nosmt' like 'mitigations=auto,no_user_kernel'. The global options come first in the mitigations= string. Cross-thread mitigations can either remain enabled fully, including potentially disabling SMT ('auto,nosmt'), remain enabled except for disabling SMT ('auto'), or entirely disabled through the new 'no_cross_thread' attack vector option. The default settings for these attack vectors are consistent with existing kernel defaults, other than the automatic disabling of VM-based attack vectors if KVM support is not present. Signed-off-by: David Kaplan Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/20250707183316.1349127-3-david.kaplan@amd.com --- diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 6378370a952f6..1fb143ee1ffa7 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -198,9 +198,25 @@ void cpuhp_report_idle_dead(void); static inline void cpuhp_report_idle_dead(void) { } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ +enum cpu_attack_vectors { + CPU_MITIGATE_USER_KERNEL, + CPU_MITIGATE_USER_USER, + CPU_MITIGATE_GUEST_HOST, + CPU_MITIGATE_GUEST_GUEST, + NR_CPU_ATTACK_VECTORS, +}; + +enum smt_mitigations { + SMT_MITIGATIONS_OFF, + SMT_MITIGATIONS_AUTO, + SMT_MITIGATIONS_ON, +}; + #ifdef CONFIG_CPU_MITIGATIONS extern bool cpu_mitigations_off(void); extern bool cpu_mitigations_auto_nosmt(void); +extern bool cpu_attack_vector_mitigated(enum cpu_attack_vectors v); +extern enum smt_mitigations smt_mitigations; #else static inline bool cpu_mitigations_off(void) { @@ -210,6 +226,11 @@ static inline bool cpu_mitigations_auto_nosmt(void) { return false; } +static inline bool cpu_attack_vector_mitigated(enum cpu_attack_vectors v) +{ + return false; +} +#define smt_mitigations SMT_MITIGATIONS_OFF #endif #endif /* _LINUX_CPU_H_ */ diff --git a/kernel/cpu.c b/kernel/cpu.c index a59e009e0be46..faf0f23fc5d82 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -37,6 +37,7 @@ #include #include #include +#include #include #define CREATE_TRACE_POINTS @@ -3174,8 +3175,38 @@ void __init boot_cpu_hotplug_init(void) #ifdef CONFIG_CPU_MITIGATIONS /* - * These are used for a global "mitigations=" cmdline option for toggling - * optional CPU mitigations. + * All except the cross-thread attack vector are mitigated by default. + * Cross-thread mitigation often requires disabling SMT which is expensive + * so cross-thread mitigations are only partially enabled by default. + * + * Guest-to-Host and Guest-to-Guest vectors are only needed if KVM support is + * present. + */ +static bool attack_vectors[NR_CPU_ATTACK_VECTORS] __ro_after_init = { + [CPU_MITIGATE_USER_KERNEL] = true, + [CPU_MITIGATE_USER_USER] = true, + [CPU_MITIGATE_GUEST_HOST] = IS_ENABLED(CONFIG_KVM), + [CPU_MITIGATE_GUEST_GUEST] = IS_ENABLED(CONFIG_KVM), +}; + +bool cpu_attack_vector_mitigated(enum cpu_attack_vectors v) +{ + if (v < NR_CPU_ATTACK_VECTORS) + return attack_vectors[v]; + + WARN_ONCE(1, "Invalid attack vector %d\n", v); + return false; +} + +/* + * There are 3 global options, 'off', 'auto', 'auto,nosmt'. These may optionally + * be combined with attack-vector disables which follow them. + * + * Examples: + * mitigations=auto,no_user_kernel,no_user_user,no_cross_thread + * mitigations=auto,nosmt,no_guest_host,no_guest_guest + * + * mitigations=off is equivalent to disabling all attack vectors. */ enum cpu_mitigations { CPU_MITIGATIONS_OFF, @@ -3183,19 +3214,96 @@ enum cpu_mitigations { CPU_MITIGATIONS_AUTO_NOSMT, }; +enum { + NO_USER_KERNEL, + NO_USER_USER, + NO_GUEST_HOST, + NO_GUEST_GUEST, + NO_CROSS_THREAD, + NR_VECTOR_PARAMS, +}; + +enum smt_mitigations smt_mitigations __ro_after_init = SMT_MITIGATIONS_AUTO; static enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO; +static const match_table_t global_mitigations = { + { CPU_MITIGATIONS_AUTO_NOSMT, "auto,nosmt"}, + { CPU_MITIGATIONS_AUTO, "auto"}, + { CPU_MITIGATIONS_OFF, "off"}, +}; + +static const match_table_t vector_mitigations = { + { NO_USER_KERNEL, "no_user_kernel"}, + { NO_USER_USER, "no_user_user"}, + { NO_GUEST_HOST, "no_guest_host"}, + { NO_GUEST_GUEST, "no_guest_guest"}, + { NO_CROSS_THREAD, "no_cross_thread"}, + { NR_VECTOR_PARAMS, NULL}, +}; + +static int __init mitigations_parse_global_opt(char *arg) +{ + int i; + + for (i = 0; i < ARRAY_SIZE(global_mitigations); i++) { + const char *pattern = global_mitigations[i].pattern; + + if (!strncmp(arg, pattern, strlen(pattern))) { + cpu_mitigations = global_mitigations[i].token; + return strlen(pattern); + } + } + + return 0; +} + static int __init mitigations_parse_cmdline(char *arg) { - if (!strcmp(arg, "off")) - cpu_mitigations = CPU_MITIGATIONS_OFF; - else if (!strcmp(arg, "auto")) - cpu_mitigations = CPU_MITIGATIONS_AUTO; - else if (!strcmp(arg, "auto,nosmt")) - cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT; - else - pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n", - arg); + char *s, *p; + int len; + + len = mitigations_parse_global_opt(arg); + + if (cpu_mitigations_off()) { + memset(attack_vectors, 0, sizeof(attack_vectors)); + smt_mitigations = SMT_MITIGATIONS_OFF; + } else if (cpu_mitigations_auto_nosmt()) { + smt_mitigations = SMT_MITIGATIONS_ON; + } + + p = arg + len; + + if (!*p) + return 0; + + /* Attack vector controls may come after the ',' */ + if (*p++ != ',' || !IS_ENABLED(CONFIG_ARCH_HAS_CPU_ATTACK_VECTORS)) { + pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n", arg); + return 0; + } + + while ((s = strsep(&p, ",")) != NULL) { + switch (match_token(s, vector_mitigations, NULL)) { + case NO_USER_KERNEL: + attack_vectors[CPU_MITIGATE_USER_KERNEL] = false; + break; + case NO_USER_USER: + attack_vectors[CPU_MITIGATE_USER_USER] = false; + break; + case NO_GUEST_HOST: + attack_vectors[CPU_MITIGATE_GUEST_HOST] = false; + break; + case NO_GUEST_GUEST: + attack_vectors[CPU_MITIGATE_GUEST_GUEST] = false; + break; + case NO_CROSS_THREAD: + smt_mitigations = SMT_MITIGATIONS_OFF; + break; + default: + pr_crit("Unsupported mitigations options %s\n", s); + return 0; + } + } return 0; }