512 lines
12 KiB
C
512 lines
12 KiB
C
/*
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* Code for replacing ftrace calls with jumps.
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*
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* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
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*
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* Thanks goes to Ingo Molnar, for suggesting the idea.
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* Mathieu Desnoyers, for suggesting postponing the modifications.
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* Arjan van de Ven, for keeping me straight, and explaining to me
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* the dangers of modifying code on the run.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/spinlock.h>
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#include <linux/hardirq.h>
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#include <linux/uaccess.h>
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#include <linux/ftrace.h>
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#include <linux/percpu.h>
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#include <linux/sched.h>
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#include <linux/init.h>
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#include <linux/list.h>
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#include <trace/syscall.h>
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#include <asm/cacheflush.h>
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#include <asm/ftrace.h>
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#include <asm/nops.h>
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#include <asm/nmi.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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/*
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* modifying_code is set to notify NMIs that they need to use
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* memory barriers when entering or exiting. But we don't want
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* to burden NMIs with unnecessary memory barriers when code
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* modification is not being done (which is most of the time).
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*
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* A mutex is already held when ftrace_arch_code_modify_prepare
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* and post_process are called. No locks need to be taken here.
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*
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* Stop machine will make sure currently running NMIs are done
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* and new NMIs will see the updated variable before we need
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* to worry about NMIs doing memory barriers.
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*/
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static int modifying_code __read_mostly;
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static DEFINE_PER_CPU(int, save_modifying_code);
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int ftrace_arch_code_modify_prepare(void)
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{
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set_kernel_text_rw();
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modifying_code = 1;
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return 0;
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}
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int ftrace_arch_code_modify_post_process(void)
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{
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modifying_code = 0;
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set_kernel_text_ro();
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return 0;
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}
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union ftrace_code_union {
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char code[MCOUNT_INSN_SIZE];
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struct {
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char e8;
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int offset;
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} __attribute__((packed));
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};
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static int ftrace_calc_offset(long ip, long addr)
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{
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return (int)(addr - ip);
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}
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static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
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{
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static union ftrace_code_union calc;
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calc.e8 = 0xe8;
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calc.offset = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
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/*
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* No locking needed, this must be called via kstop_machine
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* which in essence is like running on a uniprocessor machine.
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*/
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return calc.code;
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}
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/*
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* Modifying code must take extra care. On an SMP machine, if
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* the code being modified is also being executed on another CPU
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* that CPU will have undefined results and possibly take a GPF.
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* We use kstop_machine to stop other CPUS from exectuing code.
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* But this does not stop NMIs from happening. We still need
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* to protect against that. We separate out the modification of
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* the code to take care of this.
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*
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* Two buffers are added: An IP buffer and a "code" buffer.
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*
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* 1) Put the instruction pointer into the IP buffer
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* and the new code into the "code" buffer.
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* 2) Wait for any running NMIs to finish and set a flag that says
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* we are modifying code, it is done in an atomic operation.
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* 3) Write the code
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* 4) clear the flag.
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* 5) Wait for any running NMIs to finish.
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*
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* If an NMI is executed, the first thing it does is to call
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* "ftrace_nmi_enter". This will check if the flag is set to write
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* and if it is, it will write what is in the IP and "code" buffers.
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*
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* The trick is, it does not matter if everyone is writing the same
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* content to the code location. Also, if a CPU is executing code
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* it is OK to write to that code location if the contents being written
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* are the same as what exists.
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*/
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#define MOD_CODE_WRITE_FLAG (1 << 31) /* set when NMI should do the write */
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static atomic_t nmi_running = ATOMIC_INIT(0);
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static int mod_code_status; /* holds return value of text write */
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static void *mod_code_ip; /* holds the IP to write to */
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static void *mod_code_newcode; /* holds the text to write to the IP */
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static unsigned nmi_wait_count;
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static atomic_t nmi_update_count = ATOMIC_INIT(0);
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int ftrace_arch_read_dyn_info(char *buf, int size)
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{
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int r;
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r = snprintf(buf, size, "%u %u",
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nmi_wait_count,
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atomic_read(&nmi_update_count));
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return r;
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}
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static void clear_mod_flag(void)
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{
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int old = atomic_read(&nmi_running);
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for (;;) {
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int new = old & ~MOD_CODE_WRITE_FLAG;
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if (old == new)
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break;
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old = atomic_cmpxchg(&nmi_running, old, new);
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}
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}
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static void ftrace_mod_code(void)
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{
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/*
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* Yes, more than one CPU process can be writing to mod_code_status.
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* (and the code itself)
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* But if one were to fail, then they all should, and if one were
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* to succeed, then they all should.
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*/
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mod_code_status = probe_kernel_write(mod_code_ip, mod_code_newcode,
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MCOUNT_INSN_SIZE);
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/* if we fail, then kill any new writers */
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if (mod_code_status)
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clear_mod_flag();
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}
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void ftrace_nmi_enter(void)
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{
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__get_cpu_var(save_modifying_code) = modifying_code;
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if (!__get_cpu_var(save_modifying_code))
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return;
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if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
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smp_rmb();
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ftrace_mod_code();
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atomic_inc(&nmi_update_count);
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}
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/* Must have previous changes seen before executions */
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smp_mb();
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}
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void ftrace_nmi_exit(void)
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{
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if (!__get_cpu_var(save_modifying_code))
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return;
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/* Finish all executions before clearing nmi_running */
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smp_mb();
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atomic_dec(&nmi_running);
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}
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static void wait_for_nmi_and_set_mod_flag(void)
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{
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if (!atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG))
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return;
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do {
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cpu_relax();
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} while (atomic_cmpxchg(&nmi_running, 0, MOD_CODE_WRITE_FLAG));
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nmi_wait_count++;
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}
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static void wait_for_nmi(void)
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{
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if (!atomic_read(&nmi_running))
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return;
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do {
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cpu_relax();
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} while (atomic_read(&nmi_running));
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nmi_wait_count++;
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}
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static inline int
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within(unsigned long addr, unsigned long start, unsigned long end)
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{
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return addr >= start && addr < end;
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}
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static int
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do_ftrace_mod_code(unsigned long ip, void *new_code)
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{
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/*
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* On x86_64, kernel text mappings are mapped read-only with
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* CONFIG_DEBUG_RODATA. So we use the kernel identity mapping instead
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* of the kernel text mapping to modify the kernel text.
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*
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* For 32bit kernels, these mappings are same and we can use
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* kernel identity mapping to modify code.
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*/
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if (within(ip, (unsigned long)_text, (unsigned long)_etext))
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ip = (unsigned long)__va(__pa(ip));
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mod_code_ip = (void *)ip;
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mod_code_newcode = new_code;
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/* The buffers need to be visible before we let NMIs write them */
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smp_mb();
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wait_for_nmi_and_set_mod_flag();
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/* Make sure all running NMIs have finished before we write the code */
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smp_mb();
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ftrace_mod_code();
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/* Make sure the write happens before clearing the bit */
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smp_mb();
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clear_mod_flag();
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wait_for_nmi();
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return mod_code_status;
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}
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static unsigned char ftrace_nop[MCOUNT_INSN_SIZE];
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static unsigned char *ftrace_nop_replace(void)
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{
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return ftrace_nop;
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}
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static int
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ftrace_modify_code(unsigned long ip, unsigned char *old_code,
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unsigned char *new_code)
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{
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unsigned char replaced[MCOUNT_INSN_SIZE];
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/*
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* Note: Due to modules and __init, code can
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* disappear and change, we need to protect against faulting
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* as well as code changing. We do this by using the
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* probe_kernel_* functions.
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*
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* No real locking needed, this code is run through
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* kstop_machine, or before SMP starts.
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*/
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/* read the text we want to modify */
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if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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/* Make sure it is what we expect it to be */
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if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
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return -EINVAL;
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/* replace the text with the new text */
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if (do_ftrace_mod_code(ip, new_code))
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return -EPERM;
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sync_core();
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return 0;
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}
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int ftrace_make_nop(struct module *mod,
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struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned char *new, *old;
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unsigned long ip = rec->ip;
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old = ftrace_call_replace(ip, addr);
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new = ftrace_nop_replace();
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return ftrace_modify_code(rec->ip, old, new);
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}
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int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned char *new, *old;
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unsigned long ip = rec->ip;
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old = ftrace_nop_replace();
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new = ftrace_call_replace(ip, addr);
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return ftrace_modify_code(rec->ip, old, new);
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}
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int ftrace_update_ftrace_func(ftrace_func_t func)
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{
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unsigned long ip = (unsigned long)(&ftrace_call);
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unsigned char old[MCOUNT_INSN_SIZE], *new;
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int ret;
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memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
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new = ftrace_call_replace(ip, (unsigned long)func);
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ret = ftrace_modify_code(ip, old, new);
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return ret;
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}
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int __init ftrace_dyn_arch_init(void *data)
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{
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extern const unsigned char ftrace_test_p6nop[];
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extern const unsigned char ftrace_test_nop5[];
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extern const unsigned char ftrace_test_jmp[];
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int faulted = 0;
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/*
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* There is no good nop for all x86 archs.
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* We will default to using the P6_NOP5, but first we
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* will test to make sure that the nop will actually
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* work on this CPU. If it faults, we will then
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* go to a lesser efficient 5 byte nop. If that fails
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* we then just use a jmp as our nop. This isn't the most
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* efficient nop, but we can not use a multi part nop
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* since we would then risk being preempted in the middle
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* of that nop, and if we enabled tracing then, it might
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* cause a system crash.
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*
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* TODO: check the cpuid to determine the best nop.
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*/
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asm volatile (
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"ftrace_test_jmp:"
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"jmp ftrace_test_p6nop\n"
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"nop\n"
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"nop\n"
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"nop\n" /* 2 byte jmp + 3 bytes */
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"ftrace_test_p6nop:"
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P6_NOP5
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"jmp 1f\n"
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"ftrace_test_nop5:"
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".byte 0x66,0x66,0x66,0x66,0x90\n"
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"1:"
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".section .fixup, \"ax\"\n"
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"2: movl $1, %0\n"
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" jmp ftrace_test_nop5\n"
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"3: movl $2, %0\n"
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" jmp 1b\n"
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".previous\n"
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_ASM_EXTABLE(ftrace_test_p6nop, 2b)
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_ASM_EXTABLE(ftrace_test_nop5, 3b)
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: "=r"(faulted) : "0" (faulted));
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switch (faulted) {
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case 0:
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pr_info("converting mcount calls to 0f 1f 44 00 00\n");
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memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE);
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break;
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case 1:
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pr_info("converting mcount calls to 66 66 66 66 90\n");
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memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE);
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break;
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case 2:
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pr_info("converting mcount calls to jmp . + 5\n");
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memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE);
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break;
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}
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/* The return code is retured via data */
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*(unsigned long *)data = 0;
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return 0;
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}
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#endif
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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#ifdef CONFIG_DYNAMIC_FTRACE
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extern void ftrace_graph_call(void);
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static int ftrace_mod_jmp(unsigned long ip,
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int old_offset, int new_offset)
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{
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unsigned char code[MCOUNT_INSN_SIZE];
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if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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if (code[0] != 0xe9 || old_offset != *(int *)(&code[1]))
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return -EINVAL;
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*(int *)(&code[1]) = new_offset;
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if (do_ftrace_mod_code(ip, &code))
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return -EPERM;
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return 0;
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}
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int ftrace_enable_ftrace_graph_caller(void)
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{
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unsigned long ip = (unsigned long)(&ftrace_graph_call);
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int old_offset, new_offset;
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old_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
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new_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
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return ftrace_mod_jmp(ip, old_offset, new_offset);
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}
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int ftrace_disable_ftrace_graph_caller(void)
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{
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unsigned long ip = (unsigned long)(&ftrace_graph_call);
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int old_offset, new_offset;
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old_offset = (unsigned long)(&ftrace_graph_caller) - (ip + MCOUNT_INSN_SIZE);
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new_offset = (unsigned long)(&ftrace_stub) - (ip + MCOUNT_INSN_SIZE);
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return ftrace_mod_jmp(ip, old_offset, new_offset);
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}
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#endif /* !CONFIG_DYNAMIC_FTRACE */
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/*
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* Hook the return address and push it in the stack of return addrs
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* in current thread info.
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*/
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void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
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unsigned long frame_pointer)
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{
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unsigned long old;
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int faulted;
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struct ftrace_graph_ent trace;
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unsigned long return_hooker = (unsigned long)
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&return_to_handler;
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if (unlikely(atomic_read(¤t->tracing_graph_pause)))
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return;
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/*
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* Protect against fault, even if it shouldn't
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* happen. This tool is too much intrusive to
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* ignore such a protection.
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*/
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asm volatile(
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"1: " _ASM_MOV " (%[parent]), %[old]\n"
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"2: " _ASM_MOV " %[return_hooker], (%[parent])\n"
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" movl $0, %[faulted]\n"
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"3:\n"
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".section .fixup, \"ax\"\n"
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"4: movl $1, %[faulted]\n"
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" jmp 3b\n"
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".previous\n"
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_ASM_EXTABLE(1b, 4b)
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_ASM_EXTABLE(2b, 4b)
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: [old] "=&r" (old), [faulted] "=r" (faulted)
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: [parent] "r" (parent), [return_hooker] "r" (return_hooker)
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: "memory"
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);
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if (unlikely(faulted)) {
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ftrace_graph_stop();
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WARN_ON(1);
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return;
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}
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if (ftrace_push_return_trace(old, self_addr, &trace.depth,
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frame_pointer) == -EBUSY) {
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*parent = old;
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return;
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}
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trace.func = self_addr;
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/* Only trace if the calling function expects to */
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if (!ftrace_graph_entry(&trace)) {
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current->curr_ret_stack--;
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*parent = old;
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}
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}
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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