On Mon, Nov 16, 2020 at 09:50:37AM -0500, Joel Fernandes wrote: > > > Can I add your Reviewed-by tag to below updated patch? Thanks for review! > > > > Reviewed-by: Alexandre Chartre <alexandre.char...@oracle.com> > > Will add, thanks! > > - Joel
Alexandre, there was one more trivial fixup I had to make. Just fyi: https://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git/commit/?h=coresched&id=06a302df95f3a235e2680102ec4e5da10c9b87a0 Basically, I need to conditionally call sched_core_unsafe_exit() depending on value of sched_core_protect_kernel= option and CONFIG_SCHED_CORE. Below is updated patch: diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index bd1a5b87a5e2..a36f08d74e09 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4678,6 +4678,15 @@ sbni= [NET] Granch SBNI12 leased line adapter + sched_core_protect_kernel= + [SCHED_CORE] Pause SMT siblings of a core running in + user mode, if at least one of the siblings of the core + is running in kernel mode. This is to guarantee that + kernel data is not leaked to tasks which are not trusted + by the kernel. A value of 0 disables protection, 1 + enables protection. The default is 1. Note that protection + depends on the arch defining the _TIF_UNSAFE_RET flag. + sched_debug [KNL] Enables verbose scheduler debug messages. schedstats= [KNL,X86] Enable or disable scheduled statistics. diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h index 1a128baf3628..022e1f114157 100644 --- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h @@ -33,6 +33,10 @@ # define _TIF_PATCH_PENDING (0) #endif +#ifndef _TIF_UNSAFE_RET +# define _TIF_UNSAFE_RET (0) +#endif + #ifndef _TIF_UPROBE # define _TIF_UPROBE (0) #endif @@ -74,7 +78,7 @@ #define EXIT_TO_USER_MODE_WORK \ (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \ _TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \ - ARCH_EXIT_TO_USER_MODE_WORK) + _TIF_UNSAFE_RET | ARCH_EXIT_TO_USER_MODE_WORK) /** * arch_check_user_regs - Architecture specific sanity check for user mode regs @@ -444,4 +448,10 @@ irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs); */ void noinstr irqentry_nmi_exit(struct pt_regs *regs, irqentry_state_t irq_state); +/* entry_kernel_protected - Is kernel protection on entry/exit into kernel supported? */ +static inline bool entry_kernel_protected(void) +{ + return IS_ENABLED(CONFIG_SCHED_CORE) && sched_core_kernel_protected() + && _TIF_UNSAFE_RET != 0; +} #endif diff --git a/include/linux/sched.h b/include/linux/sched.h index d38e904dd603..fe6f225bfbf9 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2071,4 +2071,16 @@ int sched_trace_rq_nr_running(struct rq *rq); const struct cpumask *sched_trace_rd_span(struct root_domain *rd); +#ifdef CONFIG_SCHED_CORE +void sched_core_unsafe_enter(void); +void sched_core_unsafe_exit(void); +bool sched_core_wait_till_safe(unsigned long ti_check); +bool sched_core_kernel_protected(void); +#else +#define sched_core_unsafe_enter(ignore) do { } while (0) +#define sched_core_unsafe_exit(ignore) do { } while (0) +#define sched_core_wait_till_safe(ignore) do { } while (0) +#define sched_core_kernel_protected(ignore) do { } while (0) +#endif + #endif diff --git a/kernel/entry/common.c b/kernel/entry/common.c index bc75c114c1b3..9d9d926f2a1c 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -28,6 +28,9 @@ static __always_inline void enter_from_user_mode(struct pt_regs *regs) instrumentation_begin(); trace_hardirqs_off_finish(); + + if (entry_kernel_protected()) + sched_core_unsafe_enter(); instrumentation_end(); } @@ -145,6 +148,26 @@ static void handle_signal_work(struct pt_regs *regs, unsigned long ti_work) arch_do_signal_or_restart(regs, ti_work & _TIF_SIGPENDING); } +static unsigned long exit_to_user_get_work(void) +{ + unsigned long ti_work = READ_ONCE(current_thread_info()->flags); + + if (!entry_kernel_protected()) + return ti_work; + +#ifdef CONFIG_SCHED_CORE + ti_work &= EXIT_TO_USER_MODE_WORK; + if ((ti_work & _TIF_UNSAFE_RET) == ti_work) { + sched_core_unsafe_exit(); + if (sched_core_wait_till_safe(EXIT_TO_USER_MODE_WORK)) { + sched_core_unsafe_enter(); /* not exiting to user yet. */ + } + } + + return READ_ONCE(current_thread_info()->flags); +#endif +} + static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, unsigned long ti_work) { @@ -182,7 +205,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, * enabled above. */ local_irq_disable_exit_to_user(); - ti_work = READ_ONCE(current_thread_info()->flags); + ti_work = exit_to_user_get_work(); } /* Return the latest work state for arch_exit_to_user_mode() */ @@ -191,9 +214,10 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, static void exit_to_user_mode_prepare(struct pt_regs *regs) { - unsigned long ti_work = READ_ONCE(current_thread_info()->flags); + unsigned long ti_work; lockdep_assert_irqs_disabled(); + ti_work = exit_to_user_get_work(); if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) ti_work = exit_to_user_mode_loop(regs, ti_work); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a5e04078ba5d..56d6a382e3ff 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -76,6 +76,27 @@ __read_mostly int scheduler_running; #ifdef CONFIG_SCHED_CORE +DEFINE_STATIC_KEY_TRUE(sched_core_protect_kernel); +static int __init set_sched_core_protect_kernel(char *str) +{ + unsigned long val = 0; + + if (!str) + return 0; + + if (!kstrtoul(str, 0, &val) && !val) + static_branch_disable(&sched_core_protect_kernel); + + return 1; +} +__setup("sched_core_protect_kernel=", set_sched_core_protect_kernel); + +/* Is the kernel protected by core scheduling? */ +bool sched_core_kernel_protected(void) +{ + return static_branch_likely(&sched_core_protect_kernel); +} + DEFINE_STATIC_KEY_FALSE(__sched_core_enabled); /* kernel prio, less is more */ @@ -4596,6 +4617,226 @@ static inline bool cookie_match(struct task_struct *a, struct task_struct *b) return a->core_cookie == b->core_cookie; } +/* + * Handler to attempt to enter kernel. It does nothing because the exit to + * usermode or guest mode will do the actual work (of waiting if needed). + */ +static void sched_core_irq_work(struct irq_work *work) +{ + return; +} + +static inline void init_sched_core_irq_work(struct rq *rq) +{ + init_irq_work(&rq->core_irq_work, sched_core_irq_work); +} + +/* + * sched_core_wait_till_safe - Pause the caller's hyperthread until the core + * exits the core-wide unsafe state. Obviously the CPU calling this function + * should not be responsible for the core being in the core-wide unsafe state + * otherwise it will deadlock. + * + * @ti_check: We spin here with IRQ enabled and preempt disabled. Break out of + * the loop if TIF flags are set and notify caller about it. + * + * IRQs should be disabled. + */ +bool sched_core_wait_till_safe(unsigned long ti_check) +{ + bool restart = false; + struct rq *rq; + int cpu; + + /* We clear the thread flag only at the end, so no need to check for it. */ + ti_check &= ~_TIF_UNSAFE_RET; + + cpu = smp_processor_id(); + rq = cpu_rq(cpu); + + if (!sched_core_enabled(rq)) + goto ret; + + /* Down grade to allow interrupts to prevent stop_machine lockups.. */ + preempt_disable(); + local_irq_enable(); + + /* + * Wait till the core of this HT is not in an unsafe state. + * + * Pair with raw_spin_lock/unlock() in sched_core_unsafe_enter/exit(). + */ + while (smp_load_acquire(&rq->core->core_unsafe_nest) > 0) { + cpu_relax(); + if (READ_ONCE(current_thread_info()->flags) & ti_check) { + restart = true; + break; + } + } + + /* Upgrade it back to the expectations of entry code. */ + local_irq_disable(); + preempt_enable(); + +ret: + if (!restart) + clear_tsk_thread_flag(current, TIF_UNSAFE_RET); + + return restart; +} + +/* + * Enter the core-wide IRQ state. Sibling will be paused if it is running + * 'untrusted' code, until sched_core_unsafe_exit() is called. Every attempt to + * avoid sending useless IPIs is made. Must be called only from hard IRQ + * context. + */ +void sched_core_unsafe_enter(void) +{ + const struct cpumask *smt_mask; + unsigned long flags; + struct rq *rq; + int i, cpu; + + if (!static_branch_likely(&sched_core_protect_kernel)) + return; + + local_irq_save(flags); + cpu = smp_processor_id(); + rq = cpu_rq(cpu); + if (!sched_core_enabled(rq)) + goto ret; + + /* Ensure that on return to user/guest, we check whether to wait. */ + if (current->core_cookie) + set_tsk_thread_flag(current, TIF_UNSAFE_RET); + + /* Count unsafe_enter() calls received without unsafe_exit() on this CPU. */ + rq->core_this_unsafe_nest++; + + /* + * Should not nest: enter() should only pair with exit(). Both are done + * during the first entry into kernel and the last exit from kernel. + * Nested kernel entries (such as nested interrupts) will only trigger + * enter() and exit() on the outer most kernel entry and exit. + */ + if (WARN_ON_ONCE(rq->core_this_unsafe_nest != 1)) + goto ret; + + raw_spin_lock(rq_lockp(rq)); + smt_mask = cpu_smt_mask(cpu); + + /* + * Contribute this CPU's unsafe_enter() to the core-wide unsafe_enter() + * count. The raw_spin_unlock() release semantics pairs with the nest + * counter's smp_load_acquire() in sched_core_wait_till_safe(). + */ + WRITE_ONCE(rq->core->core_unsafe_nest, rq->core->core_unsafe_nest + 1); + + if (WARN_ON_ONCE(rq->core->core_unsafe_nest == UINT_MAX)) + goto unlock; + + if (irq_work_is_busy(&rq->core_irq_work)) { + /* + * Do nothing more since we are in an IPI sent from another + * sibling to enforce safety. That sibling would have sent IPIs + * to all of the HTs. + */ + goto unlock; + } + + /* + * If we are not the first ones on the core to enter core-wide unsafe + * state, do nothing. + */ + if (rq->core->core_unsafe_nest > 1) + goto unlock; + + /* Do nothing more if the core is not tagged. */ + if (!rq->core->core_cookie) + goto unlock; + + for_each_cpu(i, smt_mask) { + struct rq *srq = cpu_rq(i); + + if (i == cpu || cpu_is_offline(i)) + continue; + + if (!srq->curr->mm || is_task_rq_idle(srq->curr)) + continue; + + /* Skip if HT is not running a tagged task. */ + if (!srq->curr->core_cookie && !srq->core_pick) + continue; + + /* + * Force sibling into the kernel by IPI. If work was already + * pending, no new IPIs are sent. This is Ok since the receiver + * would already be in the kernel, or on its way to it. + */ + irq_work_queue_on(&srq->core_irq_work, i); + } +unlock: + raw_spin_unlock(rq_lockp(rq)); +ret: + local_irq_restore(flags); +} + +/* + * Process any work need for either exiting the core-wide unsafe state, or for + * waiting on this hyperthread if the core is still in this state. + * + * @idle: Are we called from the idle loop? + */ +void sched_core_unsafe_exit(void) +{ + unsigned long flags; + unsigned int nest; + struct rq *rq; + int cpu; + + if (!static_branch_likely(&sched_core_protect_kernel)) + return; + + local_irq_save(flags); + cpu = smp_processor_id(); + rq = cpu_rq(cpu); + + /* Do nothing if core-sched disabled. */ + if (!sched_core_enabled(rq)) + goto ret; + + /* + * Can happen when a process is forked and the first return to user + * mode is a syscall exit. Either way, there's nothing to do. + */ + if (rq->core_this_unsafe_nest == 0) + goto ret; + + rq->core_this_unsafe_nest--; + + /* enter() should be paired with exit() only. */ + if (WARN_ON_ONCE(rq->core_this_unsafe_nest != 0)) + goto ret; + + raw_spin_lock(rq_lockp(rq)); + /* + * Core-wide nesting counter can never be 0 because we are + * still in it on this CPU. + */ + nest = rq->core->core_unsafe_nest; + WARN_ON_ONCE(!nest); + + WRITE_ONCE(rq->core->core_unsafe_nest, nest - 1); + /* + * The raw_spin_unlock release semantics pairs with the nest counter's + * smp_load_acquire() in sched_core_wait_till_safe(). + */ + raw_spin_unlock(rq_lockp(rq)); +ret: + local_irq_restore(flags); +} + // XXX fairness/fwd progress conditions /* * Returns @@ -4991,6 +5232,7 @@ static inline void sched_core_cpu_starting(unsigned int cpu) rq = cpu_rq(i); if (rq->core && rq->core == rq) core_rq = rq; + init_sched_core_irq_work(rq); } if (!core_rq) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index cd74cc41c8da..acf187c36fc4 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1063,6 +1063,8 @@ struct rq { unsigned int core_enabled; unsigned int core_sched_seq; struct rb_root core_tree; + struct irq_work core_irq_work; /* To force HT into kernel */ + unsigned int core_this_unsafe_nest; /* shared state */ unsigned int core_task_seq; @@ -1070,6 +1072,7 @@ struct rq { unsigned long core_cookie; unsigned char core_forceidle; unsigned int core_forceidle_seq; + unsigned int core_unsafe_nest; #endif };
