ftrace: Synchronize variable setting with breakpoints

[linux-2.6.git] / arch / x86 / kernel / ftrace.c

/*
 * Code for replacing ftrace calls with jumps.
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 *
 * Thanks goes to Ingo Molnar, for suggesting the idea.
 * Mathieu Desnoyers, for suggesting postponing the modifications.
 * Arjan van de Ven, for keeping me straight, and explaining to me
 * the dangers of modifying code on the run.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/module.h>

#include <trace/syscall.h>

#include <asm/cacheflush.h>
#include <asm/kprobes.h>
#include <asm/ftrace.h>
#include <asm/nops.h>

#ifdef CONFIG_DYNAMIC_FTRACE

int ftrace_arch_code_modify_prepare(void)
{
        set_kernel_text_rw();
        set_all_modules_text_rw();
        return 0;
}

int ftrace_arch_code_modify_post_process(void)
{
        set_all_modules_text_ro();
        set_kernel_text_ro();
        return 0;
}

union ftrace_code_union {
        char code[MCOUNT_INSN_SIZE];
        struct {
                char e8;
                int offset;
        } __attribute__((packed));
};

static int ftrace_calc_offset(long ip, long addr)
{
        return (int)(addr - ip);
}

static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
{
        static union ftrace_code_union calc;

        calc.e8         = 0xe8;
        calc.offset     = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);

        /*
         * No locking needed, this must be called via kstop_machine
         * which in essence is like running on a uniprocessor machine.
         */
        return calc.code;
}

static inline int
within(unsigned long addr, unsigned long start, unsigned long end)
{
        return addr >= start && addr < end;
}

static int
do_ftrace_mod_code(unsigned long ip, const void *new_code)
{
        /*
         * On x86_64, kernel text mappings are mapped read-only with
         * CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
         * of the kernel text mapping to modify the kernel text.
         *
         * For 32bit kernels, these mappings are same and we can use
         * kernel identity mapping to modify code.
         */
        if (within(ip, (unsigned long)_text, (unsigned long)_etext))
                ip = (unsigned long)__va(__pa(ip));

        return probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE);
}

static const unsigned char *ftrace_nop_replace(void)
{
        return ideal_nops[NOP_ATOMIC5];
}

static int
ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
                   unsigned const char *new_code)
{
        unsigned char replaced[MCOUNT_INSN_SIZE];

        /*
         * Note: Due to modules and __init, code can
         *  disappear and change, we need to protect against faulting
         *  as well as code changing. We do this by using the
         *  probe_kernel_* functions.
         *
         * No real locking needed, this code is run through
         * kstop_machine, or before SMP starts.
         */

        /* read the text we want to modify */
        if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
                return -EFAULT;

        /* Make sure it is what we expect it to be */
        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
                return -EINVAL;

        /* replace the text with the new text */
        if (do_ftrace_mod_code(ip, new_code))
                return -EPERM;

        sync_core();

        return 0;
}

int ftrace_make_nop(struct module *mod,
                    struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned const char *new, *old;
        unsigned long ip = rec->ip;

        old = ftrace_call_replace(ip, addr);
        new = ftrace_nop_replace();

        return ftrace_modify_code(rec->ip, old, new);
}

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned const char *new, *old;
        unsigned long ip = rec->ip;

        old = ftrace_nop_replace();
        new = ftrace_call_replace(ip, addr);

        return ftrace_modify_code(rec->ip, old, new);
}

int ftrace_update_ftrace_func(ftrace_func_t func)
{
        unsigned long ip = (unsigned long)(&ftrace_call);
        unsigned char old[MCOUNT_INSN_SIZE], *new;
        int ret;

        memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
        new = ftrace_call_replace(ip, (unsigned long)func);
        ret = ftrace_modify_code(ip, old, new);

        return ret;
}

/*
 * The modifying_ftrace_code is used to tell the breakpoint
 * handler to call ftrace_int3_handler(). If it fails to
 * call this handler for a breakpoint added by ftrace, then
 * the kernel may crash.
 *
 * As atomic_writes on x86 do not need a barrier, we do not
 * need to add smp_mb()s for this to work. It is also considered
 * that we can not read the modifying_ftrace_code before
 * executing the breakpoint. That would be quite remarkable if
 * it could do that. Here's the flow that is required:
 *
 *   CPU-0                          CPU-1
 *
 * atomic_inc(mfc);
 * write int3s
 *                              <trap-int3> // implicit (r)mb
 *                              if (atomic_read(mfc))
 *                                      call ftrace_int3_handler()
 *
 * Then when we are finished:
 *
 * atomic_dec(mfc);
 *
 * If we hit a breakpoint that was not set by ftrace, it does not
 * matter if ftrace_int3_handler() is called or not. It will
 * simply be ignored. But it is crucial that a ftrace nop/caller
 * breakpoint is handled. No other user should ever place a
 * breakpoint on an ftrace nop/caller location. It must only
 * be done by this code.
 */
atomic_t modifying_ftrace_code __read_mostly;

/*
 * A breakpoint was added to the code address we are about to
 * modify, and this is the handle that will just skip over it.
 * We are either changing a nop into a trace call, or a trace
 * call to a nop. While the change is taking place, we treat
 * it just like it was a nop.
 */
int ftrace_int3_handler(struct pt_regs *regs)
{
        if (WARN_ON_ONCE(!regs))
                return 0;

        if (!ftrace_location(regs->ip - 1))
                return 0;

        regs->ip += MCOUNT_INSN_SIZE - 1;

        return 1;
}

static int ftrace_write(unsigned long ip, const char *val, int size)
{
        /*
         * On x86_64, kernel text mappings are mapped read-only with
         * CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
         * of the kernel text mapping to modify the kernel text.
         *
         * For 32bit kernels, these mappings are same and we can use
         * kernel identity mapping to modify code.
         */
        if (within(ip, (unsigned long)_text, (unsigned long)_etext))
                ip = (unsigned long)__va(__pa(ip));

        return probe_kernel_write((void *)ip, val, size);
}

static int add_break(unsigned long ip, const char *old)
{
        unsigned char replaced[MCOUNT_INSN_SIZE];
        unsigned char brk = BREAKPOINT_INSTRUCTION;

        if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
                return -EFAULT;

        /* Make sure it is what we expect it to be */
        if (memcmp(replaced, old, MCOUNT_INSN_SIZE) != 0)
                return -EINVAL;

        if (ftrace_write(ip, &brk, 1))
                return -EPERM;

        return 0;
}

static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned const char *old;
        unsigned long ip = rec->ip;

        old = ftrace_call_replace(ip, addr);

        return add_break(rec->ip, old);
}


static int add_brk_on_nop(struct dyn_ftrace *rec)
{
        unsigned const char *old;

        old = ftrace_nop_replace();

        return add_break(rec->ip, old);
}

static int add_breakpoints(struct dyn_ftrace *rec, int enable)
{
        unsigned long ftrace_addr;
        int ret;

        ret = ftrace_test_record(rec, enable);

        ftrace_addr = (unsigned long)FTRACE_ADDR;

        switch (ret) {
        case FTRACE_UPDATE_IGNORE:
                return 0;

        case FTRACE_UPDATE_MAKE_CALL:
                /* converting nop to call */
                return add_brk_on_nop(rec);

        case FTRACE_UPDATE_MAKE_NOP:
                /* converting a call to a nop */
                return add_brk_on_call(rec, ftrace_addr);
        }
        return 0;
}

/*
 * On error, we need to remove breakpoints. This needs to
 * be done caefully. If the address does not currently have a
 * breakpoint, we know we are done. Otherwise, we look at the
 * remaining 4 bytes of the instruction. If it matches a nop
 * we replace the breakpoint with the nop. Otherwise we replace
 * it with the call instruction.
 */
static int remove_breakpoint(struct dyn_ftrace *rec)
{
        unsigned char ins[MCOUNT_INSN_SIZE];
        unsigned char brk = BREAKPOINT_INSTRUCTION;
        const unsigned char *nop;
        unsigned long ftrace_addr;
        unsigned long ip = rec->ip;

        /* If we fail the read, just give up */
        if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
                return -EFAULT;

        /* If this does not have a breakpoint, we are done */
        if (ins[0] != brk)
                return -1;

        nop = ftrace_nop_replace();

        /*
         * If the last 4 bytes of the instruction do not match
         * a nop, then we assume that this is a call to ftrace_addr.
         */
        if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
                /*
                 * For extra paranoidism, we check if the breakpoint is on
                 * a call that would actually jump to the ftrace_addr.
                 * If not, don't touch the breakpoint, we make just create
                 * a disaster.
                 */
                ftrace_addr = (unsigned long)FTRACE_ADDR;
                nop = ftrace_call_replace(ip, ftrace_addr);

                if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
                        return -EINVAL;
        }

        return probe_kernel_write((void *)ip, &nop[0], 1);
}

static int add_update_code(unsigned long ip, unsigned const char *new)
{
        /* skip breakpoint */
        ip++;
        new++;
        if (ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1))
                return -EPERM;
        return 0;
}

static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned long ip = rec->ip;
        unsigned const char *new;

        new = ftrace_call_replace(ip, addr);
        return add_update_code(ip, new);
}

static int add_update_nop(struct dyn_ftrace *rec)
{
        unsigned long ip = rec->ip;
        unsigned const char *new;

        new = ftrace_nop_replace();
        return add_update_code(ip, new);
}

static int add_update(struct dyn_ftrace *rec, int enable)
{
        unsigned long ftrace_addr;
        int ret;

        ret = ftrace_test_record(rec, enable);

        ftrace_addr = (unsigned long)FTRACE_ADDR;

        switch (ret) {
        case FTRACE_UPDATE_IGNORE:
                return 0;

        case FTRACE_UPDATE_MAKE_CALL:
                /* converting nop to call */
                return add_update_call(rec, ftrace_addr);

        case FTRACE_UPDATE_MAKE_NOP:
                /* converting a call to a nop */
                return add_update_nop(rec);
        }

        return 0;
}

static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
{
        unsigned long ip = rec->ip;
        unsigned const char *new;

        new = ftrace_call_replace(ip, addr);

        if (ftrace_write(ip, new, 1))
                return -EPERM;

        return 0;
}

static int finish_update_nop(struct dyn_ftrace *rec)
{
        unsigned long ip = rec->ip;
        unsigned const char *new;

        new = ftrace_nop_replace();

        if (ftrace_write(ip, new, 1))
                return -EPERM;
        return 0;
}

static int finish_update(struct dyn_ftrace *rec, int enable)
{
        unsigned long ftrace_addr;
        int ret;

        ret = ftrace_update_record(rec, enable);

        ftrace_addr = (unsigned long)FTRACE_ADDR;

        switch (ret) {
        case FTRACE_UPDATE_IGNORE:
                return 0;

        case FTRACE_UPDATE_MAKE_CALL:
                /* converting nop to call */
                return finish_update_call(rec, ftrace_addr);

        case FTRACE_UPDATE_MAKE_NOP:
                /* converting a call to a nop */
                return finish_update_nop(rec);
        }

        return 0;
}

static void do_sync_core(void *data)
{
        sync_core();
}

static void run_sync(void)
{
        int enable_irqs = irqs_disabled();

        /* We may be called with interrupts disbled (on bootup). */
        if (enable_irqs)
                local_irq_enable();
        on_each_cpu(do_sync_core, NULL, 1);
        if (enable_irqs)
                local_irq_disable();
}

void ftrace_replace_code(int enable)
{
        struct ftrace_rec_iter *iter;
        struct dyn_ftrace *rec;
        const char *report = "adding breakpoints";
        int count = 0;
        int ret;

        for_ftrace_rec_iter(iter) {
                rec = ftrace_rec_iter_record(iter);

                ret = add_breakpoints(rec, enable);
                if (ret)
                        goto remove_breakpoints;
                count++;
        }

        run_sync();

        report = "updating code";

        for_ftrace_rec_iter(iter) {
                rec = ftrace_rec_iter_record(iter);

                ret = add_update(rec, enable);
                if (ret)
                        goto remove_breakpoints;
        }

        run_sync();

        report = "removing breakpoints";

        for_ftrace_rec_iter(iter) {
                rec = ftrace_rec_iter_record(iter);

                ret = finish_update(rec, enable);
                if (ret)
                        goto remove_breakpoints;
        }

        run_sync();

        return;

 remove_breakpoints:
        ftrace_bug(ret, rec ? rec->ip : 0);
        printk(KERN_WARNING "Failed on %s (%d):\n", report, count);
        for_ftrace_rec_iter(iter) {
                rec = ftrace_rec_iter_record(iter);
                remove_breakpoint(rec);
        }
}

void arch_ftrace_update_code(int command)
{
        /* See comment above by declaration of modifying_ftrace_code */
        atomic_inc(&modifying_ftrace_code);

        ftrace_modify_all_code(command);

        atomic_dec(&modifying_ftrace_code);
}

int __init ftrace_dyn_arch_init(void *data)
{
        /* The return code is retured via data */
        *(unsigned long *)data = 0;

        return 0;
}
#endif

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

#ifdef CONFIG_DYNAMIC_FTRACE
extern void ftrace_graph_call(void);

static int ftrace_mod_jmp(unsigned long ip,
                          int old_offset, int new_offset)
{
        unsigned char code[MCOUNT_INSN_SIZE];

        if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
                return -EFAULT;

        if (code[0] != 0xe9 || old_offset != *(int *)(&code[1]))
                return -EINVAL;

        *(int *)(&code[1]) = new_offset;

        if (do_ftrace_mod_code(ip, &code))
                return -EPERM;

        return 0;
}

int ftrace_enable_ftrace_graph_caller(void)
{
        unsigned long ip = (unsigned long)(&ftrace_graph_call);
        int old_offset, new_offset;

        old_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
        new_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);

        return ftrace_mod_jmp(ip, old_offset, new_offset);
}

int ftrace_disable_ftrace_graph_caller(void)
{
        unsigned long ip = (unsigned long)(&ftrace_graph_call);
        int old_offset, new_offset;

        old_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
        new_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);

        return ftrace_mod_jmp(ip, old_offset, new_offset);
}

#endif /* !CONFIG_DYNAMIC_FTRACE */

/*
 * Hook the return address and push it in the stack of return addrs
 * in current thread info.
 */
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
                           unsigned long frame_pointer)
{
        unsigned long old;
        int faulted;
        struct ftrace_graph_ent trace;
        unsigned long return_hooker = (unsigned long)
                                &return_to_handler;

        if (unlikely(atomic_read(&current->tracing_graph_pause)))
                return;

        /*
         * Protect against fault, even if it shouldn't
         * happen. This tool is too much intrusive to
         * ignore such a protection.
         */
        asm volatile(
                "1: " _ASM_MOV " (%[parent]), %[old]\n"
                "2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
                "   movl $0, %[faulted]\n"
                "3:\n"

                ".section .fixup, \"ax\"\n"
                "4: movl $1, %[faulted]\n"
                "   jmp 3b\n"
                ".previous\n"

                _ASM_EXTABLE(1b, 4b)
                _ASM_EXTABLE(2b, 4b)

                : [old] "=&r" (old), [faulted] "=r" (faulted)
                : [parent] "r" (parent), [return_hooker] "r" (return_hooker)
                : "memory"
        );

        if (unlikely(faulted)) {
                ftrace_graph_stop();
                WARN_ON(1);
                return;
        }

        trace.func = self_addr;
        trace.depth = current->curr_ret_stack + 1;

        /* Only trace if the calling function expects to */
        if (!ftrace_graph_entry(&trace)) {
                *parent = old;
                return;
        }

        if (ftrace_push_return_trace(old, self_addr, &trace.depth,
                    frame_pointer) == -EBUSY) {
                *parent = old;
                return;
        }
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */