/*
* 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 <trace/syscall.h>
#include <asm/cacheflush.h>
#include <asm/ftrace.h>
#include <asm/nops.h>
#include <asm/nmi.h>
#ifdef CONFIG_DYNAMIC_FTRACE
/*
* modifying_code is set to notify NMIs that they need to use
* memory barriers when entering or exiting. But we don't want
* to burden NMIs with unnecessary memory barriers when code
* modification is not being done (which is most of the time).
*
* A mutex is already held when ftrace_arch_code_modify_prepare
* and post_process are called. No locks need to be taken here.
*
* Stop machine will make sure currently running NMIs are done
* and new NMIs will see the updated variable before we need
* to worry about NMIs doing memory barriers.
*/
static int modifying_code __read_mostly;
static DEFINE_PER_CPU(int, save_modifying_code);
int ftrace_arch_code_modify_prepare(void)
{
set_kernel_text_rw();
modifying_code = 1;
return 0;
}
int ftrace_arch_code_modify_post_process(void)
{
modifying_code = 0;
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;
}
/*
* Modifying code must take extra care. On an SMP machine, if
* the code being modified is also being executed on another CPU
* that CPU will have undefined results and possibly take a GPF.
* We use kstop_machine to stop other CPUS from exectuing code.
* But this does not stop NMIs from happening. We still need
* to protect against that. We separate out the modification of
* the code to take care of this.
*
* Two buffers are added: An IP buffer and a "code" buffer.
*
* 1) Put the instruction pointer into the IP buffer
* and the new code into the "code" buffer.
* 2) Wait for any running NMIs to finish and set a flag that says
* we are modifying code, it is done in an atomic operation.
* 3) Write the code
* 4) clear the flag.
* 5) Wait for any running NMIs to finish.
*
* If an NMI is executed, the first thing it does is to call
* "ftrace_nmi_enter". This will check if the flag is set to write
* and if it is, it will write what is in the IP and "code" buffers.
*
* The trick is, it does not matter if everyone is writing the same
* content to the code location. Also, if a CPU is executing code
* it is OK to write to that code location if the contents being written
* are the same as what exists.
*/
#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
static atomic_t nmi_running = ATOMIC_INIT(0);
static int mod_code_status; /* holds return value of text write */
static void *mod_code_ip; /* holds the IP to write to */
static void *mod_code_newcode; /* holds the text to write to the IP */
static unsigned nmi_wait_count;
static atomic_t nmi_update_count = ATOMIC_INIT(0);
int ftrace_arch_read_dyn_info(char *buf, int size)
{
int r;
r = snprintf(buf, size, "%u %u",
nmi_wait_count,
atomic_read(&nmi_update_count));
return r;
}
static void clear_mod_flag(void)
{
int old = atomic_read(&nmi_running);
for (;;) {
int new = old & ~MOD_CODE_WRITE_FLAG;
if (old == new)
break;
old = atomic_cmpxchg(&nmi_running, old, new);
}
}
static void ftrace_mod_code(void)
{
/*
* Yes, more than one CPU process can be writing to mod_code_status.
* (and the code itself)
* But if one were to fail, then they all should, and if one were
* to succeed, then they all should.
*/
mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
MCOUNT_INSN_SIZE);
/* if we fail, then kill any new writers */
if (mod_code_status)
clear_mod_flag();
}
void ftrace_nmi_enter(void)
{
__get_cpu_var(save_modifying_code) = modifying_code;
if (!__get_cpu_var(save_modifying_code))
return;
if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
smp_rmb();
ftrace_mod_code();
atomic_inc(&nmi_update_count);
}
/* Must have previous changes seen before executions */
smp_mb();
}
void ftrace_nmi_exit(void)
{
if (!__get_cpu_var(save_modifying_code))
return;
/* Finish all executions before clearing nmi_running */
smp_mb();
atomic_dec(&nmi_running);
}
static void wait_for_nmi_and_set_mod_flag(void)
{
if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
return;
do {
cpu_relax();
} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
nmi_wait_count++;
}
static void wait_for_nmi(void)
{
if (!atomic_read(&nmi_running))
return;
do {
cpu_relax();
} while (atomic_read(&nmi_running));
nmi_wait_count++;
}
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, 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));
mod_code_ip = (void *)ip;
mod_code_newcode = new_code;
/* The buffers need to be visible before we let NMIs write them */
smp_mb();
wait_for_nmi_and_set_mod_flag();
/* Make sure all running NMIs have finished before we write the code */
smp_mb();
ftrace_mod_code();
/* Make sure the write happens before clearing the bit */
smp_mb();
clear_mod_flag();
wait_for_nmi();
return mod_code_status;
}
static unsigned char *ftrace_nop_replace(void)
{
return ideal_nop5;
}
static int
ftrace_modify_code(unsigned long ip, unsigned char *old_code,
unsigned 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 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 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;
}
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(¤t->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;
}
if (ftrace_push_return_trace(old, self_addr, &trace.depth,
frame_pointer) == -EBUSY) {
*parent = old;
return;
}
trace.func = self_addr;
/* Only trace if the calling function expects to */
if (!ftrace_graph_entry(&trace)) {
current->curr_ret_stack--;
*parent = old;
}
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
