Messages in this thread Patch in this message | | | From | Tim Chen <> | Subject | Re: [Patch v4 17/18] x86/speculation: Update SPEC_CTRL MSRs of remote CPUs | Date | Tue, 6 Nov 2018 16:18:17 -0800 |
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Thomas,
> >>> 2) Add _TIF_UPDATE_SPEC_CTRL to the SYSCALL_EXIT_WORK_FLAGS and handle it >>> in the slow work path. >> >> There can be tasks that don't do any syscalls, and it seems like we can >> have MSRs getting out of sync? > > Setting the TIF flag directly in a remote task is wrong. It needs to be > handled when the _TIF_UPDATE_SPEC_CTRL is evaluated, i.e. the information > needs to be stored process wide e.g. in task->mm. > > But yes, if the remote task runs in user space forever, it won't > help. Though the point is that dumpable is usually set when the process > starts, so it's probably mostly a theoretical issue. >
I took a crack to implement what you suggested to update remote task's flag and remote SPEC_CTRL MSR on the syscall exit slow path.
This looks reasobale?
Tim
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diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 3b2490b..614594a 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -216,7 +216,7 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) #define SYSCALL_EXIT_WORK_FLAGS \ (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \ - _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT) + _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT | _TIF_UPDATE_SPEC_CTRL) static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) { @@ -227,6 +227,8 @@ static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) if (cached_flags & _TIF_SYSCALL_TRACEPOINT) trace_sys_exit(regs, regs->ax); + if (cached_flags & _TIF_UPDATE_SPEC_CTRL) + spec_ctrl_do_pending_update(); /* * If TIF_SYSCALL_EMU is set, we only get here because of * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP). diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index c59a6c4..f124597 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -276,6 +276,8 @@ static inline void indirect_branch_prediction_barrier(void) alternative_msr_write(MSR_IA32_PRED_CMD, val, X86_FEATURE_USE_IBPB); } +void spec_ctrl_do_pending_update(void); + /* The Intel SPEC CTRL MSR base value cache */ extern u64 x86_spec_ctrl_base; diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 4f6a7a9..b78db59 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -97,6 +97,7 @@ struct thread_info { #define TIF_USER_RETURN_NOTIFY 14 /* Notify kernel of userspace return */ #define TIF_PATCH_PENDING 15 /* Pending live patching update */ #define TIF_FSCHECK 16 /* Check FS is USER_DS on return */ +#define TIF_UPDATE_SPEC_CTRL 17 /* Pending update of speculation control */ /* Task status */ #define TIF_UPROBE 18 /* Breakpointed or singlestepping */ @@ -131,6 +132,7 @@ struct thread_info { #define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY) #define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING) #define _TIF_FSCHECK (1 << TIF_FSCHECK) +#define _TIF_UPDATE_SPEC_CTRL (1 << TIF_UPDATE_SPEC_CTRL) #define _TIF_UPROBE (1 << TIF_UPROBE) #define _TIF_MEMDIE (1 << TIF_MEMDIE) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 4c15c86..d82d3f8 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -14,6 +14,8 @@ #include <linux/module.h> #include <linux/nospec.h> #include <linux/prctl.h> +#include <linux/sched/coredump.h> +#include <linux/sched/signal.h> #include <asm/spec-ctrl.h> #include <asm/cmdline.h> @@ -770,6 +772,69 @@ static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl) return 0; } +static void set_task_stibp(struct task_struct *tsk, bool stibp_on) +{ + bool update = false; + + if (stibp_on) + update = !test_and_set_tsk_thread_flag(tsk, TIF_STIBP); + else + update = test_and_clear_tsk_thread_flag(tsk, TIF_STIBP); + + if (tsk == current && update) + speculation_ctrl_update_current(); +} + +void spec_ctrl_do_pending_update(void) +{ + if (!static_branch_unlikely(&spectre_v2_app_lite)) + return; + + if (!current->mm) + return; + + if (get_dumpable(current->mm) != SUID_DUMP_USER) + set_tsk_thread_flag(current, TIF_STIBP); + else + clear_tsk_thread_flag(current, TIF_STIBP); + + clear_tsk_thread_flag(current, TIF_UPDATE_SPEC_CTRL); + speculation_ctrl_update_current(); +} + +int arch_update_spec_ctrl_restriction(struct task_struct *task) +{ + unsigned long flags; + struct task_struct *t; + bool stibp_on = false; + + if (!static_branch_unlikely(&spectre_v2_app_lite)) + return 0; + + if (!task->mm) + return -EINVAL; + + if (!lock_task_sighand(task, &flags)) + return -ESRCH; + + if (get_dumpable(task->mm) != SUID_DUMP_USER) + stibp_on = true; + + for_each_thread(task, t) { + if (task_cpu(task) == smp_processor_id()) + set_task_stibp(task, stibp_on); + else if (test_tsk_thread_flag(task, TIF_STIBP) != stibp_on) + set_tsk_thread_flag(task, TIF_UPDATE_SPEC_CTRL); + } + + unlock_task_sighand(task, &flags); + return 0; +} + int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which, unsigned long ctrl) {
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