diff options
Diffstat (limited to 'arch/x86/mm/tlb.c')
| -rw-r--r-- | arch/x86/mm/tlb.c | 198 |
1 files changed, 122 insertions, 76 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index e96b99eb800c..bddd6b3cee1d 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -7,6 +7,7 @@ #include <linux/export.h> #include <linux/cpu.h> #include <linux/debugfs.h> +#include <linux/ptrace.h> #include <asm/tlbflush.h> #include <asm/mmu_context.h> @@ -180,13 +181,29 @@ static void sync_current_stack_to_mm(struct mm_struct *mm) } } +static bool ibpb_needed(struct task_struct *tsk, u64 last_ctx_id) +{ + /* + * Check if the current (previous) task has access to the memory + * of the @tsk (next) task. If access is denied, make sure to + * issue a IBPB to stop user->user Spectre-v2 attacks. + * + * Note: __ptrace_may_access() returns 0 or -ERRNO. + */ + return (tsk && tsk->mm && tsk->mm->context.ctx_id != last_ctx_id && + ptrace_may_access_sched(tsk, PTRACE_MODE_SPEC_IBPB)); +} + void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk) { struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm); u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid); + bool was_lazy = this_cpu_read(cpu_tlbstate.is_lazy); unsigned cpu = smp_processor_id(); u64 next_tlb_gen; + bool need_flush; + u16 new_asid; /* * NB: The scheduler will call us with prev == next when switching @@ -240,20 +257,41 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, next->context.ctx_id); /* - * We don't currently support having a real mm loaded without - * our cpu set in mm_cpumask(). We have all the bookkeeping - * in place to figure out whether we would need to flush - * if our cpu were cleared in mm_cpumask(), but we don't - * currently use it. + * Even in lazy TLB mode, the CPU should stay set in the + * mm_cpumask. The TLB shootdown code can figure out from + * from cpu_tlbstate.is_lazy whether or not to send an IPI. */ if (WARN_ON_ONCE(real_prev != &init_mm && !cpumask_test_cpu(cpu, mm_cpumask(next)))) cpumask_set_cpu(cpu, mm_cpumask(next)); - return; + /* + * If the CPU is not in lazy TLB mode, we are just switching + * from one thread in a process to another thread in the same + * process. No TLB flush required. + */ + if (!was_lazy) + return; + + /* + * Read the tlb_gen to check whether a flush is needed. + * If the TLB is up to date, just use it. + * The barrier synchronizes with the tlb_gen increment in + * the TLB shootdown code. + */ + smp_mb(); + next_tlb_gen = atomic64_read(&next->context.tlb_gen); + if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) == + next_tlb_gen) + return; + + /* + * TLB contents went out of date while we were in lazy + * mode. Fall through to the TLB switching code below. + */ + new_asid = prev_asid; + need_flush = true; } else { - u16 new_asid; - bool need_flush; u64 last_ctx_id = this_cpu_read(cpu_tlbstate.last_ctx_id); /* @@ -262,18 +300,13 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * one process from doing Spectre-v2 attacks on another. * * As an optimization, flush indirect branches only when - * switching into processes that disable dumping. This - * protects high value processes like gpg, without having - * too high performance overhead. IBPB is *expensive*! - * - * This will not flush branches when switching into kernel - * threads. It will also not flush if we switch to idle - * thread and back to the same process. It will flush if we - * switch to a different non-dumpable process. + * switching into a processes that can't be ptrace by the + * current one (as in such case, attacker has much more + * convenient way how to tamper with the next process than + * branch buffer poisoning). */ - if (tsk && tsk->mm && - tsk->mm->context.ctx_id != last_ctx_id && - get_dumpable(tsk->mm) != SUID_DUMP_USER) + if (static_cpu_has(X86_FEATURE_USE_IBPB) && + ibpb_needed(tsk, last_ctx_id)) indirect_branch_prediction_barrier(); if (IS_ENABLED(CONFIG_VMAP_STACK)) { @@ -308,46 +341,48 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, /* Let nmi_uaccess_okay() know that we're changing CR3. */ this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING); barrier(); + } - if (need_flush) { - this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id); - this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen); - load_new_mm_cr3(next->pgd, new_asid, true); - - /* - * NB: This gets called via leave_mm() in the idle path - * where RCU functions differently. Tracing normally - * uses RCU, so we need to use the _rcuidle variant. - * - * (There is no good reason for this. The idle code should - * be rearranged to call this before rcu_idle_enter().) - */ - trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); - } else { - /* The new ASID is already up to date. */ - load_new_mm_cr3(next->pgd, new_asid, false); - - /* See above wrt _rcuidle. */ - trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, 0); - } + if (need_flush) { + this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id); + this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen); + load_new_mm_cr3(next->pgd, new_asid, true); /* - * Record last user mm's context id, so we can avoid - * flushing branch buffer with IBPB if we switch back - * to the same user. + * NB: This gets called via leave_mm() in the idle path + * where RCU functions differently. Tracing normally + * uses RCU, so we need to use the _rcuidle variant. + * + * (There is no good reason for this. The idle code should + * be rearranged to call this before rcu_idle_enter().) */ - if (next != &init_mm) - this_cpu_write(cpu_tlbstate.last_ctx_id, next->context.ctx_id); - - /* Make sure we write CR3 before loaded_mm. */ - barrier(); + trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL); + } else { + /* The new ASID is already up to date. */ + load_new_mm_cr3(next->pgd, new_asid, false); - this_cpu_write(cpu_tlbstate.loaded_mm, next); - this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid); + /* See above wrt _rcuidle. */ + trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, 0); } - load_mm_cr4(next); - switch_ldt(real_prev, next); + /* + * Record last user mm's context id, so we can avoid + * flushing branch buffer with IBPB if we switch back + * to the same user. + */ + if (next != &init_mm) + this_cpu_write(cpu_tlbstate.last_ctx_id, next->context.ctx_id); + + /* Make sure we write CR3 before loaded_mm. */ + barrier(); + + this_cpu_write(cpu_tlbstate.loaded_mm, next); + this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid); + + if (next != real_prev) { + load_mm_cr4(next); + switch_ldt(real_prev, next); + } } /* @@ -368,20 +403,7 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm) return; - if (tlb_defer_switch_to_init_mm()) { - /* - * There's a significant optimization that may be possible - * here. We have accurate enough TLB flush tracking that we - * don't need to maintain coherence of TLB per se when we're - * lazy. We do, however, need to maintain coherence of - * paging-structure caches. We could, in principle, leave our - * old mm loaded and only switch to init_mm when - * tlb_remove_page() happens. - */ - this_cpu_write(cpu_tlbstate.is_lazy, true); - } else { - switch_mm(NULL, &init_mm, NULL); - } + this_cpu_write(cpu_tlbstate.is_lazy, true); } /* @@ -468,6 +490,9 @@ static void flush_tlb_func_common(const struct flush_tlb_info *f, * paging-structure cache to avoid speculatively reading * garbage into our TLB. Since switching to init_mm is barely * slower than a minimal flush, just switch to init_mm. + * + * This should be rare, with native_flush_tlb_others skipping + * IPIs to lazy TLB mode CPUs. */ switch_mm_irqs_off(NULL, &init_mm, NULL); return; @@ -528,17 +553,16 @@ static void flush_tlb_func_common(const struct flush_tlb_info *f, f->new_tlb_gen == local_tlb_gen + 1 && f->new_tlb_gen == mm_tlb_gen) { /* Partial flush */ - unsigned long addr; - unsigned long nr_pages = (f->end - f->start) >> PAGE_SHIFT; + unsigned long nr_invalidate = (f->end - f->start) >> f->stride_shift; + unsigned long addr = f->start; - addr = f->start; while (addr < f->end) { __flush_tlb_one_user(addr); - addr += PAGE_SIZE; + addr += 1UL << f->stride_shift; } if (local) - count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_pages); - trace_tlb_flush(reason, nr_pages); + count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_invalidate); + trace_tlb_flush(reason, nr_invalidate); } else { /* Full flush. */ local_flush_tlb(); @@ -571,6 +595,11 @@ static void flush_tlb_func_remote(void *info) flush_tlb_func_common(f, false, TLB_REMOTE_SHOOTDOWN); } +static bool tlb_is_not_lazy(int cpu, void *data) +{ + return !per_cpu(cpu_tlbstate.is_lazy, cpu); +} + void native_flush_tlb_others(const struct cpumask *cpumask, const struct flush_tlb_info *info) { @@ -606,8 +635,23 @@ void native_flush_tlb_others(const struct cpumask *cpumask, (void *)info, 1); return; } - smp_call_function_many(cpumask, flush_tlb_func_remote, + + /* + * If no page tables were freed, we can skip sending IPIs to + * CPUs in lazy TLB mode. They will flush the CPU themselves + * at the next context switch. + * + * However, if page tables are getting freed, we need to send the + * IPI everywhere, to prevent CPUs in lazy TLB mode from tripping + * up on the new contents of what used to be page tables, while + * doing a speculative memory access. + */ + if (info->freed_tables) + smp_call_function_many(cpumask, flush_tlb_func_remote, (void *)info, 1); + else + on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func_remote, + (void *)info, 1, GFP_ATOMIC, cpumask); } /* @@ -623,12 +667,15 @@ void native_flush_tlb_others(const struct cpumask *cpumask, static unsigned long tlb_single_page_flush_ceiling __read_mostly = 33; void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, - unsigned long end, unsigned long vmflag) + unsigned long end, unsigned int stride_shift, + bool freed_tables) { int cpu; struct flush_tlb_info info __aligned(SMP_CACHE_BYTES) = { .mm = mm, + .stride_shift = stride_shift, + .freed_tables = freed_tables, }; cpu = get_cpu(); @@ -638,8 +685,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, /* Should we flush just the requested range? */ if ((end != TLB_FLUSH_ALL) && - !(vmflag & VM_HUGETLB) && - ((end - start) >> PAGE_SHIFT) <= tlb_single_page_flush_ceiling) { + ((end - start) >> stride_shift) <= tlb_single_page_flush_ceiling) { info.start = start; info.end = end; } else { |