From dbfe2953f63c640463c630746cd5d9de8b2f63ae Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Tue, 25 Sep 2018 14:38:18 +0200 Subject: x86/speculation: Apply IBPB more strictly to avoid cross-process data leak Currently, IBPB is only issued in cases when switching into a non-dumpable process, the rationale being to protect such 'important and security sensitive' processess (such as GPG) from data leaking into a different userspace process via spectre v2. This is however completely insufficient to provide proper userspace-to-userpace spectrev2 protection, as any process can poison branch buffers before being scheduled out, and the newly scheduled process immediately becomes spectrev2 victim. In order to minimize the performance impact (for usecases that do require spectrev2 protection), issue the barrier only in cases when switching between processess where the victim can't be ptraced by the potential attacker (as in such cases, the attacker doesn't have to bother with branch buffers at all). [ tglx: Split up PTRACE_MODE_NOACCESS_CHK into PTRACE_MODE_SCHED and PTRACE_MODE_IBPB to be able to do ptrace() context tracking reasonably fine-grained ] Fixes: 18bf3c3ea8 ("x86/speculation: Use Indirect Branch Prediction Barrier in context switch") Originally-by: Tim Chen Signed-off-by: Jiri Kosina Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Andrea Arcangeli Cc: "WoodhouseDavid" Cc: Andi Kleen Cc: "SchauflerCasey" Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251437340.15880@cbobk.fhfr.pm --- kernel/ptrace.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'kernel') diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 21fec73d45d4..99cfddde6a55 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -261,6 +261,9 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state) static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode) { + if (mode & PTRACE_MODE_SCHED) + return false; + if (mode & PTRACE_MODE_NOAUDIT) return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE); else @@ -328,9 +331,16 @@ ok: !ptrace_has_cap(mm->user_ns, mode))) return -EPERM; + if (mode & PTRACE_MODE_SCHED) + return 0; return security_ptrace_access_check(task, mode); } +bool ptrace_may_access_sched(struct task_struct *task, unsigned int mode) +{ + return __ptrace_may_access(task, mode | PTRACE_MODE_SCHED); +} + bool ptrace_may_access(struct task_struct *task, unsigned int mode) { int err; -- cgit v1.2.3 From 53c613fe6349994f023245519265999eed75957f Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Tue, 25 Sep 2018 14:38:55 +0200 Subject: x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation STIBP is a feature provided by certain Intel ucodes / CPUs. This feature (once enabled) prevents cross-hyperthread control of decisions made by indirect branch predictors. Enable this feature if - the CPU is vulnerable to spectre v2 - the CPU supports SMT and has SMT siblings online - spectre_v2 mitigation autoselection is enabled (default) After some previous discussion, this leaves STIBP on all the time, as wrmsr on crossing kernel boundary is a no-no. This could perhaps later be a bit more optimized (like disabling it in NOHZ, experiment with disabling it in idle, etc) if needed. Note that the synchronization of the mask manipulation via newly added spec_ctrl_mutex is currently not strictly needed, as the only updater is already being serialized by cpu_add_remove_lock, but let's make this a little bit more future-proof. Signed-off-by: Jiri Kosina Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Andrea Arcangeli Cc: "WoodhouseDavid" Cc: Andi Kleen Cc: Tim Chen Cc: "SchauflerCasey" Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251438240.15880@cbobk.fhfr.pm --- arch/x86/kernel/cpu/bugs.c | 57 +++++++++++++++++++++++++++++++++++++++++----- kernel/cpu.c | 11 ++++++++- 2 files changed, 61 insertions(+), 7 deletions(-) (limited to 'kernel') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 40bdaea97fe7..53eb14a65610 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -35,12 +35,10 @@ static void __init spectre_v2_select_mitigation(void); static void __init ssb_select_mitigation(void); static void __init l1tf_select_mitigation(void); -/* - * Our boot-time value of the SPEC_CTRL MSR. We read it once so that any - * writes to SPEC_CTRL contain whatever reserved bits have been set. - */ -u64 __ro_after_init x86_spec_ctrl_base; +/* The base value of the SPEC_CTRL MSR that always has to be preserved. */ +u64 x86_spec_ctrl_base; EXPORT_SYMBOL_GPL(x86_spec_ctrl_base); +static DEFINE_MUTEX(spec_ctrl_mutex); /* * The vendor and possibly platform specific bits which can be modified in @@ -325,6 +323,46 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) return cmd; } +static bool stibp_needed(void) +{ + if (spectre_v2_enabled == SPECTRE_V2_NONE) + return false; + + if (!boot_cpu_has(X86_FEATURE_STIBP)) + return false; + + return true; +} + +static void update_stibp_msr(void *info) +{ + wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); +} + +void arch_smt_update(void) +{ + u64 mask; + + if (!stibp_needed()) + return; + + mutex_lock(&spec_ctrl_mutex); + mask = x86_spec_ctrl_base; + if (cpu_smt_control == CPU_SMT_ENABLED) + mask |= SPEC_CTRL_STIBP; + else + mask &= ~SPEC_CTRL_STIBP; + + if (mask != x86_spec_ctrl_base) { + pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n", + cpu_smt_control == CPU_SMT_ENABLED ? + "Enabling" : "Disabling"); + x86_spec_ctrl_base = mask; + on_each_cpu(update_stibp_msr, NULL, 1); + } + mutex_unlock(&spec_ctrl_mutex); +} + static void __init spectre_v2_select_mitigation(void) { enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); @@ -424,6 +462,9 @@ specv2_set_mode: setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); pr_info("Enabling Restricted Speculation for firmware calls\n"); } + + /* Enable STIBP if appropriate */ + arch_smt_update(); } #undef pr_fmt @@ -814,6 +855,8 @@ static ssize_t l1tf_show_state(char *buf) static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr, char *buf, unsigned int bug) { + int ret; + if (!boot_cpu_has_bug(bug)) return sprintf(buf, "Not affected\n"); @@ -831,10 +874,12 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr return sprintf(buf, "Mitigation: __user pointer sanitization\n"); case X86_BUG_SPECTRE_V2: - return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled], + ret = sprintf(buf, "%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled], boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "", boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "", + (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "", spectre_v2_module_string()); + return ret; case X86_BUG_SPEC_STORE_BYPASS: return sprintf(buf, "%s\n", ssb_strings[ssb_mode]); diff --git a/kernel/cpu.c b/kernel/cpu.c index aa7fe85ad62e..2fb49916ea56 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2025,6 +2025,12 @@ static void cpuhp_online_cpu_device(unsigned int cpu) kobject_uevent(&dev->kobj, KOBJ_ONLINE); } +/* + * Architectures that need SMT-specific errata handling during SMT hotplug + * should override this. + */ +void __weak arch_smt_update(void) { }; + static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) { int cpu, ret = 0; @@ -2051,8 +2057,10 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) */ cpuhp_offline_cpu_device(cpu); } - if (!ret) + if (!ret) { cpu_smt_control = ctrlval; + arch_smt_update(); + } cpu_maps_update_done(); return ret; } @@ -2063,6 +2071,7 @@ static int cpuhp_smt_enable(void) cpu_maps_update_begin(); cpu_smt_control = CPU_SMT_ENABLED; + arch_smt_update(); for_each_present_cpu(cpu) { /* Skip online CPUs and CPUs on offline nodes */ if (cpu_online(cpu) || !node_online(cpu_to_node(cpu))) -- cgit v1.2.3