Add command line control for user space indirect branch speculation mitigations. The new option is: spectre_v2_user= The initial options are: - on: Unconditionally enabled - off: Unconditionally disabled -auto: Kernel selects mitigation (default off for now) When the spectre_v2= command line argument is either 'on' or 'off' this implies that the application to application control follows that state even if a contradicting spectre_v2_user= argument is supplied. Originally-by: Tim Chen Signed-off-by: Thomas Gleixner --- V1 -> V2: Change the option to spectre_v2_user= --- Documentation/admin-guide/kernel-parameters.txt | 32 +++++ arch/x86/include/asm/nospec-branch.h | 10 + arch/x86/kernel/cpu/bugs.c | 133 ++++++++++++++++++++---- 3 files changed, 156 insertions(+), 19 deletions(-) --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4194,9 +4194,13 @@ spectre_v2= [X86] Control mitigation of Spectre variant 2 (indirect branch speculation) vulnerability. + The default operation protects the kernel from + user space attacks. - on - unconditionally enable - off - unconditionally disable + on - unconditionally enable, implies + spectre_v2_user=on + off - unconditionally disable, implies + spectre_v2_user=off auto - kernel detects whether your CPU model is vulnerable @@ -4206,6 +4210,12 @@ CONFIG_RETPOLINE configuration option, and the compiler with which the kernel was built. + Selecting 'on' will also enable the mitigation + against user space to user space task attacks. + + Selecting 'off' will disable both the kernel and + the user space protections. + Specific mitigations can also be selected manually: retpoline - replace indirect branches @@ -4215,6 +4225,24 @@ Not specifying this option is equivalent to spectre_v2=auto. + spectre_v2_user= + [X86] Control mitigation of Spectre variant 2 + (indirect branch speculation) vulnerability between + user space tasks + + on - Unconditionally enable mitigations. Is + enforced by spectre_v2=on + + off - Unconditionally disable mitigations. Is + enforced by spectre_v2=off + + auto - Kernel selects the mitigation depending on + the available CPU features and vulnerability. + Default is off. + + Not specifying this option is equivalent to + spectre_v2_user=auto. + spec_store_bypass_disable= [HW] Control Speculative Store Bypass (SSB) Disable mitigation (Speculative Store Bypass vulnerability) --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -3,6 +3,8 @@ #ifndef _ASM_X86_NOSPEC_BRANCH_H_ #define _ASM_X86_NOSPEC_BRANCH_H_ +#include + #include #include #include @@ -226,6 +228,12 @@ enum spectre_v2_mitigation { SPECTRE_V2_IBRS_ENHANCED, }; +/* The indirect branch speculation control variants */ +enum spectre_v2_user_mitigation { + SPECTRE_V2_USER_NONE, + SPECTRE_V2_USER_STRICT, +}; + /* The Speculative Store Bypass disable variants */ enum ssb_mitigation { SPEC_STORE_BYPASS_NONE, @@ -303,6 +311,8 @@ do { \ preempt_enable(); \ } while (0) +DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); + #endif /* __ASSEMBLY__ */ /* --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -54,6 +54,9 @@ static u64 __ro_after_init x86_spec_ctrl u64 __ro_after_init x86_amd_ls_cfg_base; u64 __ro_after_init x86_amd_ls_cfg_ssbd_mask; +/* Control conditional STIPB in switch_to() */ +DEFINE_STATIC_KEY_FALSE(switch_to_cond_stibp); + void __init check_bugs(void) { identify_boot_cpu(); @@ -199,6 +202,9 @@ static void x86_amd_ssb_disable(void) static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = SPECTRE_V2_NONE; +static enum spectre_v2_user_mitigation spectre_v2_user __ro_after_init = + SPECTRE_V2_USER_NONE; + #ifdef RETPOLINE static bool spectre_v2_bad_module; @@ -237,6 +243,104 @@ enum spectre_v2_mitigation_cmd { SPECTRE_V2_CMD_RETPOLINE_AMD, }; +enum spectre_v2_user_cmd { + SPECTRE_V2_USER_CMD_NONE, + SPECTRE_V2_USER_CMD_AUTO, + SPECTRE_V2_USER_CMD_FORCE, +}; + +static const char * const spectre_v2_user_strings[] = { + [SPECTRE_V2_USER_NONE] = "User space: Vulnerable", + [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection", +}; + +static const struct { + const char *option; + enum spectre_v2_user_cmd cmd; + bool secure; +} v2_user_options[] __initdata = { + { "auto", SPECTRE_V2_USER_CMD_AUTO, false }, + { "off", SPECTRE_V2_USER_CMD_NONE, false }, + { "on", SPECTRE_V2_USER_CMD_FORCE, true }, +}; + +static void __init spec_v2_user_print_cond(const char *reason, bool secure) +{ + if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure) + pr_info("spectre_v2_user=%s forced on command line.\n", reason); +} + +static enum spectre_v2_user_cmd __init +spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd) +{ + char arg[20]; + int ret, i; + + switch (v2_cmd) { + case SPECTRE_V2_CMD_NONE: + return SPECTRE_V2_USER_CMD_NONE; + case SPECTRE_V2_CMD_FORCE: + return SPECTRE_V2_USER_CMD_FORCE; + default: + break; + } + + ret = cmdline_find_option(boot_command_line, "spectre_v2_user", + arg, sizeof(arg)); + if (ret < 0) + return SPECTRE_V2_USER_CMD_AUTO; + + for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) { + if (match_option(arg, ret, v2_user_options[i].option)) { + spec_v2_user_print_cond(v2_user_options[i].option, + v2_user_options[i].secure); + return v2_user_options[i].cmd; + } + } + + pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg); + return SPECTRE_V2_USER_CMD_AUTO; +} + +static void __init +spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd) +{ + enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE; + bool smt_possible = IS_ENABLED(CONFIG_SMP); + + if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP)) + return; + + if (cpu_smt_control == CPU_SMT_FORCE_DISABLED || + cpu_smt_control == CPU_SMT_NOT_SUPPORTED) + smt_possible = false; + + switch (spectre_v2_parse_user_cmdline(v2_cmd)) { + case SPECTRE_V2_USER_CMD_AUTO: + case SPECTRE_V2_USER_CMD_NONE: + goto set_mode; + case SPECTRE_V2_USER_CMD_FORCE: + mode = SPECTRE_V2_USER_STRICT; + break; + } + + /* Initialize Indirect Branch Prediction Barrier */ + if (boot_cpu_has(X86_FEATURE_IBPB)) { + setup_force_cpu_cap(X86_FEATURE_USE_IBPB); + pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n"); + } + + /* If enhanced IBRS is enabled no STIPB required */ + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) + return; + +set_mode: + spectre_v2_user = mode; + /* Only print the STIBP mode when SMT possible */ + if (smt_possible) + pr_info("%s\n", spectre_v2_user_strings[mode]); +} + static const char * const spectre_v2_strings[] = { [SPECTRE_V2_NONE] = "Vulnerable", [SPECTRE_V2_RETPOLINE_GENERIC] = "Mitigation: Full generic retpoline", @@ -385,12 +489,6 @@ static void __init spectre_v2_select_mit setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n"); - /* Initialize Indirect Branch Prediction Barrier if supported */ - if (boot_cpu_has(X86_FEATURE_IBPB)) { - setup_force_cpu_cap(X86_FEATURE_USE_IBPB); - pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n"); - } - /* * Retpoline means the kernel is safe because it has no indirect * branches. Enhanced IBRS protects firmware too, so, enable restricted @@ -407,23 +505,21 @@ static void __init spectre_v2_select_mit pr_info("Enabling Restricted Speculation for firmware calls\n"); } + /* Set up IBPB and STIBP depending on the general spectre V2 command */ + spectre_v2_user_select_mitigation(cmd); + /* Enable STIBP if appropriate */ arch_smt_update(); } static bool stibp_needed(void) { - if (spectre_v2_enabled == SPECTRE_V2_NONE) - return false; - /* Enhanced IBRS makes using STIBP unnecessary. */ if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) return false; - if (!boot_cpu_has(X86_FEATURE_STIBP)) - return false; - - return true; + /* Check for strict user mitigation mode */ + return spectre_v2_user == SPECTRE_V2_USER_STRICT; } static void update_stibp_msr(void *info) @@ -844,10 +940,13 @@ static char *stibp_state(void) if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) return ""; - if (x86_spec_ctrl_base & SPEC_CTRL_STIBP) - return ", STIBP"; - else - return ""; + switch (spectre_v2_user) { + case SPECTRE_V2_USER_NONE: + return ", STIBP: disabled"; + case SPECTRE_V2_USER_STRICT: + return ", STIBP: forced"; + } + return ""; } static char *ibpb_state(void)