| // SPDX-License-Identifier: GPL-2.0 |
| /* Support for MMIO probes. |
| * Benfit many code from kprobes |
| * (C) 2002 Louis Zhuang <louis.zhuang@intel.com>. |
| * 2007 Alexander Eichner |
| * 2008 Pekka Paalanen <pq@iki.fi> |
| */ |
| |
| #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
| |
| #include <linux/list.h> |
| #include <linux/rculist.h> |
| #include <linux/spinlock.h> |
| #include <linux/hash.h> |
| #include <linux/export.h> |
| #include <linux/kernel.h> |
| #include <linux/uaccess.h> |
| #include <linux/ptrace.h> |
| #include <linux/preempt.h> |
| #include <linux/percpu.h> |
| #include <linux/kdebug.h> |
| #include <linux/mutex.h> |
| #include <linux/io.h> |
| #include <linux/slab.h> |
| #include <asm/cacheflush.h> |
| #include <asm/tlbflush.h> |
| #include <linux/errno.h> |
| #include <asm/debugreg.h> |
| #include <linux/mmiotrace.h> |
| |
| #define KMMIO_PAGE_HASH_BITS 4 |
| #define KMMIO_PAGE_TABLE_SIZE (1 << KMMIO_PAGE_HASH_BITS) |
| |
| struct kmmio_fault_page { |
| struct list_head list; |
| struct kmmio_fault_page *release_next; |
| unsigned long addr; /* the requested address */ |
| pteval_t old_presence; /* page presence prior to arming */ |
| bool armed; |
| |
| /* |
| * Number of times this page has been registered as a part |
| * of a probe. If zero, page is disarmed and this may be freed. |
| * Used only by writers (RCU) and post_kmmio_handler(). |
| * Protected by kmmio_lock, when linked into kmmio_page_table. |
| */ |
| int count; |
| |
| bool scheduled_for_release; |
| }; |
| |
| struct kmmio_delayed_release { |
| struct rcu_head rcu; |
| struct kmmio_fault_page *release_list; |
| }; |
| |
| struct kmmio_context { |
| struct kmmio_fault_page *fpage; |
| struct kmmio_probe *probe; |
| unsigned long saved_flags; |
| unsigned long addr; |
| int active; |
| }; |
| |
| static DEFINE_SPINLOCK(kmmio_lock); |
| |
| /* Protected by kmmio_lock */ |
| unsigned int kmmio_count; |
| |
| /* Read-protected by RCU, write-protected by kmmio_lock. */ |
| static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE]; |
| static LIST_HEAD(kmmio_probes); |
| |
| static struct list_head *kmmio_page_list(unsigned long addr) |
| { |
| unsigned int l; |
| pte_t *pte = lookup_address(addr, &l); |
| |
| if (!pte) |
| return NULL; |
| addr &= page_level_mask(l); |
| |
| return &kmmio_page_table[hash_long(addr, KMMIO_PAGE_HASH_BITS)]; |
| } |
| |
| /* Accessed per-cpu */ |
| static DEFINE_PER_CPU(struct kmmio_context, kmmio_ctx); |
| |
| /* |
| * this is basically a dynamic stabbing problem: |
| * Could use the existing prio tree code or |
| * Possible better implementations: |
| * The Interval Skip List: A Data Structure for Finding All Intervals That |
| * Overlap a Point (might be simple) |
| * Space Efficient Dynamic Stabbing with Fast Queries - Mikkel Thorup |
| */ |
| /* Get the kmmio at this addr (if any). You must be holding RCU read lock. */ |
| static struct kmmio_probe *get_kmmio_probe(unsigned long addr) |
| { |
| struct kmmio_probe *p; |
| list_for_each_entry_rcu(p, &kmmio_probes, list) { |
| if (addr >= p->addr && addr < (p->addr + p->len)) |
| return p; |
| } |
| return NULL; |
| } |
| |
| /* You must be holding RCU read lock. */ |
| static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long addr) |
| { |
| struct list_head *head; |
| struct kmmio_fault_page *f; |
| unsigned int l; |
| pte_t *pte = lookup_address(addr, &l); |
| |
| if (!pte) |
| return NULL; |
| addr &= page_level_mask(l); |
| head = kmmio_page_list(addr); |
| list_for_each_entry_rcu(f, head, list) { |
| if (f->addr == addr) |
| return f; |
| } |
| return NULL; |
| } |
| |
| static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old) |
| { |
| pmd_t new_pmd; |
| pmdval_t v = pmd_val(*pmd); |
| if (clear) { |
| *old = v; |
| new_pmd = pmd_mknotpresent(*pmd); |
| } else { |
| /* Presume this has been called with clear==true previously */ |
| new_pmd = __pmd(*old); |
| } |
| set_pmd(pmd, new_pmd); |
| } |
| |
| static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old) |
| { |
| pteval_t v = pte_val(*pte); |
| if (clear) { |
| *old = v; |
| /* Nothing should care about address */ |
| pte_clear(&init_mm, 0, pte); |
| } else { |
| /* Presume this has been called with clear==true previously */ |
| set_pte_atomic(pte, __pte(*old)); |
| } |
| } |
| |
| static int clear_page_presence(struct kmmio_fault_page *f, bool clear) |
| { |
| unsigned int level; |
| pte_t *pte = lookup_address(f->addr, &level); |
| |
| if (!pte) { |
| pr_err("no pte for addr 0x%08lx\n", f->addr); |
| return -1; |
| } |
| |
| switch (level) { |
| case PG_LEVEL_2M: |
| clear_pmd_presence((pmd_t *)pte, clear, &f->old_presence); |
| break; |
| case PG_LEVEL_4K: |
| clear_pte_presence(pte, clear, &f->old_presence); |
| break; |
| default: |
| pr_err("unexpected page level 0x%x.\n", level); |
| return -1; |
| } |
| |
| __flush_tlb_one_kernel(f->addr); |
| return 0; |
| } |
| |
| /* |
| * Mark the given page as not present. Access to it will trigger a fault. |
| * |
| * Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the |
| * protection is ignored here. RCU read lock is assumed held, so the struct |
| * will not disappear unexpectedly. Furthermore, the caller must guarantee, |
| * that double arming the same virtual address (page) cannot occur. |
| * |
| * Double disarming on the other hand is allowed, and may occur when a fault |
| * and mmiotrace shutdown happen simultaneously. |
| */ |
| static int arm_kmmio_fault_page(struct kmmio_fault_page *f) |
| { |
| int ret; |
| WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n")); |
| if (f->armed) { |
| pr_warn("double-arm: addr 0x%08lx, ref %d, old %d\n", |
| f->addr, f->count, !!f->old_presence); |
| } |
| ret = clear_page_presence(f, true); |
| WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming at 0x%08lx failed.\n"), |
| f->addr); |
| f->armed = true; |
| return ret; |
| } |
| |
| /** Restore the given page to saved presence state. */ |
| static void disarm_kmmio_fault_page(struct kmmio_fault_page *f) |
| { |
| int ret = clear_page_presence(f, false); |
| WARN_ONCE(ret < 0, |
| KERN_ERR "kmmio disarming at 0x%08lx failed.\n", f->addr); |
| f->armed = false; |
| } |
| |
| /* |
| * This is being called from do_page_fault(). |
| * |
| * We may be in an interrupt or a critical section. Also prefecthing may |
| * trigger a page fault. We may be in the middle of process switch. |
| * We cannot take any locks, because we could be executing especially |
| * within a kmmio critical section. |
| * |
| * Local interrupts are disabled, so preemption cannot happen. |
| * Do not enable interrupts, do not sleep, and watch out for other CPUs. |
| */ |
| /* |
| * Interrupts are disabled on entry as trap3 is an interrupt gate |
| * and they remain disabled throughout this function. |
| */ |
| int kmmio_handler(struct pt_regs *regs, unsigned long addr) |
| { |
| struct kmmio_context *ctx; |
| struct kmmio_fault_page *faultpage; |
| int ret = 0; /* default to fault not handled */ |
| unsigned long page_base = addr; |
| unsigned int l; |
| pte_t *pte = lookup_address(addr, &l); |
| if (!pte) |
| return -EINVAL; |
| page_base &= page_level_mask(l); |
| |
| /* |
| * Preemption is now disabled to prevent process switch during |
| * single stepping. We can only handle one active kmmio trace |
| * per cpu, so ensure that we finish it before something else |
| * gets to run. We also hold the RCU read lock over single |
| * stepping to avoid looking up the probe and kmmio_fault_page |
| * again. |
| */ |
| preempt_disable(); |
| rcu_read_lock(); |
| |
| faultpage = get_kmmio_fault_page(page_base); |
| if (!faultpage) { |
| /* |
| * Either this page fault is not caused by kmmio, or |
| * another CPU just pulled the kmmio probe from under |
| * our feet. The latter case should not be possible. |
| */ |
| goto no_kmmio; |
| } |
| |
| ctx = this_cpu_ptr(&kmmio_ctx); |
| if (ctx->active) { |
| if (page_base == ctx->addr) { |
| /* |
| * A second fault on the same page means some other |
| * condition needs handling by do_page_fault(), the |
| * page really not being present is the most common. |
| */ |
| pr_debug("secondary hit for 0x%08lx CPU %d.\n", |
| addr, smp_processor_id()); |
| |
| if (!faultpage->old_presence) |
| pr_info("unexpected secondary hit for address 0x%08lx on CPU %d.\n", |
| addr, smp_processor_id()); |
| } else { |
| /* |
| * Prevent overwriting already in-flight context. |
| * This should not happen, let's hope disarming at |
| * least prevents a panic. |
| */ |
| pr_emerg("recursive probe hit on CPU %d, for address 0x%08lx. Ignoring.\n", |
| smp_processor_id(), addr); |
| pr_emerg("previous hit was at 0x%08lx.\n", ctx->addr); |
| disarm_kmmio_fault_page(faultpage); |
| } |
| goto no_kmmio; |
| } |
| ctx->active++; |
| |
| ctx->fpage = faultpage; |
| ctx->probe = get_kmmio_probe(page_base); |
| ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF)); |
| ctx->addr = page_base; |
| |
| if (ctx->probe && ctx->probe->pre_handler) |
| ctx->probe->pre_handler(ctx->probe, regs, addr); |
| |
| /* |
| * Enable single-stepping and disable interrupts for the faulting |
| * context. Local interrupts must not get enabled during stepping. |
| */ |
| regs->flags |= X86_EFLAGS_TF; |
| regs->flags &= ~X86_EFLAGS_IF; |
| |
| /* Now we set present bit in PTE and single step. */ |
| disarm_kmmio_fault_page(ctx->fpage); |
| |
| /* |
| * If another cpu accesses the same page while we are stepping, |
| * the access will not be caught. It will simply succeed and the |
| * only downside is we lose the event. If this becomes a problem, |
| * the user should drop to single cpu before tracing. |
| */ |
| |
| return 1; /* fault handled */ |
| |
| no_kmmio: |
| rcu_read_unlock(); |
| preempt_enable_no_resched(); |
| return ret; |
| } |
| |
| /* |
| * Interrupts are disabled on entry as trap1 is an interrupt gate |
| * and they remain disabled throughout this function. |
| * This must always get called as the pair to kmmio_handler(). |
| */ |
| static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs) |
| { |
| int ret = 0; |
| struct kmmio_context *ctx = this_cpu_ptr(&kmmio_ctx); |
| |
| if (!ctx->active) { |
| /* |
| * debug traps without an active context are due to either |
| * something external causing them (f.e. using a debugger while |
| * mmio tracing enabled), or erroneous behaviour |
| */ |
| pr_warn("unexpected debug trap on CPU %d.\n", smp_processor_id()); |
| goto out; |
| } |
| |
| if (ctx->probe && ctx->probe->post_handler) |
| ctx->probe->post_handler(ctx->probe, condition, regs); |
| |
| /* Prevent racing against release_kmmio_fault_page(). */ |
| spin_lock(&kmmio_lock); |
| if (ctx->fpage->count) |
| arm_kmmio_fault_page(ctx->fpage); |
| spin_unlock(&kmmio_lock); |
| |
| regs->flags &= ~X86_EFLAGS_TF; |
| regs->flags |= ctx->saved_flags; |
| |
| /* These were acquired in kmmio_handler(). */ |
| ctx->active--; |
| BUG_ON(ctx->active); |
| rcu_read_unlock(); |
| preempt_enable_no_resched(); |
| |
| /* |
| * if somebody else is singlestepping across a probe point, flags |
| * will have TF set, in which case, continue the remaining processing |
| * of do_debug, as if this is not a probe hit. |
| */ |
| if (!(regs->flags & X86_EFLAGS_TF)) |
| ret = 1; |
| out: |
| return ret; |
| } |
| |
| /* You must be holding kmmio_lock. */ |
| static int add_kmmio_fault_page(unsigned long addr) |
| { |
| struct kmmio_fault_page *f; |
| |
| f = get_kmmio_fault_page(addr); |
| if (f) { |
| if (!f->count) |
| arm_kmmio_fault_page(f); |
| f->count++; |
| return 0; |
| } |
| |
| f = kzalloc(sizeof(*f), GFP_ATOMIC); |
| if (!f) |
| return -1; |
| |
| f->count = 1; |
| f->addr = addr; |
| |
| if (arm_kmmio_fault_page(f)) { |
| kfree(f); |
| return -1; |
| } |
| |
| list_add_rcu(&f->list, kmmio_page_list(f->addr)); |
| |
| return 0; |
| } |
| |
| /* You must be holding kmmio_lock. */ |
| static void release_kmmio_fault_page(unsigned long addr, |
| struct kmmio_fault_page **release_list) |
| { |
| struct kmmio_fault_page *f; |
| |
| f = get_kmmio_fault_page(addr); |
| if (!f) |
| return; |
| |
| f->count--; |
| BUG_ON(f->count < 0); |
| if (!f->count) { |
| disarm_kmmio_fault_page(f); |
| if (!f->scheduled_for_release) { |
| f->release_next = *release_list; |
| *release_list = f; |
| f->scheduled_for_release = true; |
| } |
| } |
| } |
| |
| /* |
| * With page-unaligned ioremaps, one or two armed pages may contain |
| * addresses from outside the intended mapping. Events for these addresses |
| * are currently silently dropped. The events may result only from programming |
| * mistakes by accessing addresses before the beginning or past the end of a |
| * mapping. |
| */ |
| int register_kmmio_probe(struct kmmio_probe *p) |
| { |
| unsigned long flags; |
| int ret = 0; |
| unsigned long size = 0; |
| unsigned long addr = p->addr & PAGE_MASK; |
| const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK); |
| unsigned int l; |
| pte_t *pte; |
| |
| spin_lock_irqsave(&kmmio_lock, flags); |
| if (get_kmmio_probe(addr)) { |
| ret = -EEXIST; |
| goto out; |
| } |
| |
| pte = lookup_address(addr, &l); |
| if (!pte) { |
| ret = -EINVAL; |
| goto out; |
| } |
| |
| kmmio_count++; |
| list_add_rcu(&p->list, &kmmio_probes); |
| while (size < size_lim) { |
| if (add_kmmio_fault_page(addr + size)) |
| pr_err("Unable to set page fault.\n"); |
| size += page_level_size(l); |
| } |
| out: |
| spin_unlock_irqrestore(&kmmio_lock, flags); |
| /* |
| * XXX: What should I do here? |
| * Here was a call to global_flush_tlb(), but it does not exist |
| * anymore. It seems it's not needed after all. |
| */ |
| return ret; |
| } |
| EXPORT_SYMBOL(register_kmmio_probe); |
| |
| static void rcu_free_kmmio_fault_pages(struct rcu_head *head) |
| { |
| struct kmmio_delayed_release *dr = container_of( |
| head, |
| struct kmmio_delayed_release, |
| rcu); |
| struct kmmio_fault_page *f = dr->release_list; |
| while (f) { |
| struct kmmio_fault_page *next = f->release_next; |
| BUG_ON(f->count); |
| kfree(f); |
| f = next; |
| } |
| kfree(dr); |
| } |
| |
| static void remove_kmmio_fault_pages(struct rcu_head *head) |
| { |
| struct kmmio_delayed_release *dr = |
| container_of(head, struct kmmio_delayed_release, rcu); |
| struct kmmio_fault_page *f = dr->release_list; |
| struct kmmio_fault_page **prevp = &dr->release_list; |
| unsigned long flags; |
| |
| spin_lock_irqsave(&kmmio_lock, flags); |
| while (f) { |
| if (!f->count) { |
| list_del_rcu(&f->list); |
| prevp = &f->release_next; |
| } else { |
| *prevp = f->release_next; |
| f->release_next = NULL; |
| f->scheduled_for_release = false; |
| } |
| f = *prevp; |
| } |
| spin_unlock_irqrestore(&kmmio_lock, flags); |
| |
| /* This is the real RCU destroy call. */ |
| call_rcu(&dr->rcu, rcu_free_kmmio_fault_pages); |
| } |
| |
| /* |
| * Remove a kmmio probe. You have to synchronize_rcu() before you can be |
| * sure that the callbacks will not be called anymore. Only after that |
| * you may actually release your struct kmmio_probe. |
| * |
| * Unregistering a kmmio fault page has three steps: |
| * 1. release_kmmio_fault_page() |
| * Disarm the page, wait a grace period to let all faults finish. |
| * 2. remove_kmmio_fault_pages() |
| * Remove the pages from kmmio_page_table. |
| * 3. rcu_free_kmmio_fault_pages() |
| * Actually free the kmmio_fault_page structs as with RCU. |
| */ |
| void unregister_kmmio_probe(struct kmmio_probe *p) |
| { |
| unsigned long flags; |
| unsigned long size = 0; |
| unsigned long addr = p->addr & PAGE_MASK; |
| const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK); |
| struct kmmio_fault_page *release_list = NULL; |
| struct kmmio_delayed_release *drelease; |
| unsigned int l; |
| pte_t *pte; |
| |
| pte = lookup_address(addr, &l); |
| if (!pte) |
| return; |
| |
| spin_lock_irqsave(&kmmio_lock, flags); |
| while (size < size_lim) { |
| release_kmmio_fault_page(addr + size, &release_list); |
| size += page_level_size(l); |
| } |
| list_del_rcu(&p->list); |
| kmmio_count--; |
| spin_unlock_irqrestore(&kmmio_lock, flags); |
| |
| if (!release_list) |
| return; |
| |
| drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC); |
| if (!drelease) { |
| pr_crit("leaking kmmio_fault_page objects.\n"); |
| return; |
| } |
| drelease->release_list = release_list; |
| |
| /* |
| * This is not really RCU here. We have just disarmed a set of |
| * pages so that they cannot trigger page faults anymore. However, |
| * we cannot remove the pages from kmmio_page_table, |
| * because a probe hit might be in flight on another CPU. The |
| * pages are collected into a list, and they will be removed from |
| * kmmio_page_table when it is certain that no probe hit related to |
| * these pages can be in flight. RCU grace period sounds like a |
| * good choice. |
| * |
| * If we removed the pages too early, kmmio page fault handler might |
| * not find the respective kmmio_fault_page and determine it's not |
| * a kmmio fault, when it actually is. This would lead to madness. |
| */ |
| call_rcu(&drelease->rcu, remove_kmmio_fault_pages); |
| } |
| EXPORT_SYMBOL(unregister_kmmio_probe); |
| |
| static int |
| kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args) |
| { |
| struct die_args *arg = args; |
| unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err); |
| |
| if (val == DIE_DEBUG && (*dr6_p & DR_STEP)) |
| if (post_kmmio_handler(*dr6_p, arg->regs) == 1) { |
| /* |
| * Reset the BS bit in dr6 (pointed by args->err) to |
| * denote completion of processing |
| */ |
| *dr6_p &= ~DR_STEP; |
| return NOTIFY_STOP; |
| } |
| |
| return NOTIFY_DONE; |
| } |
| |
| static struct notifier_block nb_die = { |
| .notifier_call = kmmio_die_notifier |
| }; |
| |
| int kmmio_init(void) |
| { |
| int i; |
| |
| for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) |
| INIT_LIST_HEAD(&kmmio_page_table[i]); |
| |
| return register_die_notifier(&nb_die); |
| } |
| |
| void kmmio_cleanup(void) |
| { |
| int i; |
| |
| unregister_die_notifier(&nb_die); |
| for (i = 0; i < KMMIO_PAGE_TABLE_SIZE; i++) { |
| WARN_ONCE(!list_empty(&kmmio_page_table[i]), |
| KERN_ERR "kmmio_page_table not empty at cleanup, any further tracing will leak memory.\n"); |
| } |
| } |