cregit-Linux how code gets into the kernel

Release 4.14 arch/x86/mm/kmmio.c

Directory: arch/x86/mm
// 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)]; }

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Karol Herbst3360.00%150.00%
Pekka Paalanen2240.00%150.00%
Total55100.00%2100.00%

/* 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; }

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Pekka Paalanen5298.11%266.67%
Stuart Bennett11.89%133.33%
Total53100.00%3100.00%

/* 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; }

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Pekka Paalanen4755.95%250.00%
Karol Herbst3339.29%125.00%
Stuart Bennett44.76%125.00%
Total84100.00%4100.00%


static void clear_pmd_presence(pmd_t *pmd, bool clear, pmdval_t *old) { pmdval_t v = pmd_val(*pmd); if (clear) { *old = v & _PAGE_PRESENT; v &= ~_PAGE_PRESENT; } else /* presume this has been called with clear==true previously */ v |= *old; set_pmd(pmd, __pmd(v)); }

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Pekka Paalanen4878.69%480.00%
Stuart Bennett1321.31%120.00%
Total61100.00%5100.00%


static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old) { pteval_t v = pte_val(*pte); if (clear) { *old = v & _PAGE_PRESENT; v &= ~_PAGE_PRESENT; } else /* presume this has been called with clear==true previously */ v |= *old; set_pte_atomic(pte, __pte(v)); }

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Pekka Paalanen4878.69%480.00%
Stuart Bennett1321.31%120.00%
Total61100.00%5100.00%


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(f->addr); return 0; }

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Pekka Paalanen8068.97%450.00%
Stuart Bennett3126.72%225.00%
Karol Herbst43.45%112.50%
Joe Perches10.86%112.50%
Total116100.00%8100.00%

/* * 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_warning("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; }

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Pekka Paalanen5265.00%450.00%
Stuart Bennett1620.00%225.00%
Joe Perches810.00%112.50%
Karol Herbst45.00%112.50%
Total80100.00%8100.00%

/** 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; }

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Pekka Paalanen2458.54%457.14%
Stuart Bennett1536.59%228.57%
Karol Herbst24.88%114.29%
Total41100.00%7100.00%

/* * 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 = &get_cpu_var(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; } 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. */ put_cpu_var(kmmio_ctx); return 1; /* fault handled */ no_kmmio_ctx: put_cpu_var(kmmio_ctx); no_kmmio: rcu_read_unlock(); preempt_enable_no_resched(); return ret; }

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Pekka Paalanen22174.41%555.56%
Karol Herbst4214.14%111.11%
Stuart Bennett268.75%111.11%
Ingo Molnar41.35%111.11%
Joe Perches41.35%111.11%
Total297100.00%9100.00%

/* * 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 = &get_cpu_var(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_warning("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: put_cpu_var(kmmio_ctx); return ret; }

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Pekka Paalanen16297.01%666.67%
Ingo Molnar21.20%111.11%
Stuart Bennett21.20%111.11%
Joe Perches10.60%111.11%
Total167100.00%9100.00%

/* 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; }

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Pekka Paalanen9580.51%360.00%
Stuart Bennett1815.25%120.00%
Karol Herbst54.24%120.00%
Total118100.00%5100.00%

/* 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; } } }

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Pekka Paalanen7280.90%250.00%
Marcin Ślusarz1516.85%125.00%
Karol Herbst22.25%125.00%
Total89100.00%4100.00%

/* * 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; 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(p->addr)) { ret = -EEXIST; goto out; } pte = lookup_address(p->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(p->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; }

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Pekka Paalanen12475.61%466.67%
Karol Herbst3923.78%116.67%
Joe Perches10.61%116.67%
Total164100.00%6100.00%

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); }

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Pekka Paalanen6591.55%266.67%
Stuart Bennett68.45%133.33%
Total71100.00%3100.00%


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); }

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Pekka Paalanen10779.85%350.00%
Stuart Bennett1410.45%233.33%
Marcin Ślusarz139.70%116.67%
Total134100.00%6100.00%

/* * 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; 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(p->addr, &l); if (!pte) return; spin_lock_irqsave(&kmmio_lock, flags); while (size < size_lim) { release_kmmio_fault_page(p->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); }

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Pekka Paalanen14279.33%457.14%
Karol Herbst3016.76%114.29%
Marcin Ślusarz63.35%114.29%
Joe Perches10.56%114.29%
Total179100.00%7100.00%

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; }

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Pekka Paalanen5564.71%250.00%
Luca Barbieri2225.88%125.00%
K.Prasad89.41%125.00%
Total85100.00%4100.00%

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); }

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Pekka Paalanen3897.44%150.00%
Stuart Bennett12.56%150.00%
Total39100.00%2100.00%


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"); } }

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Stuart Bennett4493.62%150.00%
Pekka Paalanen36.38%150.00%
Total47100.00%2100.00%


Overall Contributors

PersonTokensPropCommitsCommitProp
Pekka Paalanen165076.46%1238.71%
Stuart Bennett2059.50%722.58%
Karol Herbst1969.08%13.23%
Marcin Ślusarz371.71%13.23%
Joe Perches231.07%13.23%
Luca Barbieri221.02%13.23%
Ingo Molnar90.42%26.45%
K.Prasad80.37%13.23%
Tejun Heo30.14%13.23%
André Goddard Rosa20.09%13.23%
Paul Gortmaker10.05%13.23%
Greg Kroah-Hartman10.05%13.23%
Shaun Patterson10.05%13.23%
Total2158100.00%31100.00%
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