/* * 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[MCOUNT_INSN_SIZE]; static unsigned char *ftrace_nop_replace(void) { return ftrace_nop; } 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) { extern const unsigned char ftrace_test_p6nop[]; extern const unsigned char ftrace_test_nop5[]; extern const unsigned char ftrace_test_jmp[]; int faulted = 0; /* * There is no good nop for all x86 archs. * We will default to using the P6_NOP5, but first we * will test to make sure that the nop will actually * work on this CPU. If it faults, we will then * go to a lesser efficient 5 byte nop. If that fails * we then just use a jmp as our nop. This isn't the most * efficient nop, but we can not use a multi part nop * since we would then risk being preempted in the middle * of that nop, and if we enabled tracing then, it might * cause a system crash. * * TODO: check the cpuid to determine the best nop. */ asm volatile ( "ftrace_test_jmp:" "jmp ftrace_test_p6nop\n" "nop\n" "nop\n" "nop\n" /* 2 byte jmp + 3 bytes */ "ftrace_test_p6nop:" P6_NOP5 "jmp 1f\n" "ftrace_test_nop5:" ".byte 0x66,0x66,0x66,0x66,0x90\n" "1:" ".section .fixup, \"ax\"\n" "2: movl $1, %0\n" " jmp ftrace_test_nop5\n" "3: movl $2, %0\n" " jmp 1b\n" ".previous\n" _ASM_EXTABLE(ftrace_test_p6nop, 2b) _ASM_EXTABLE(ftrace_test_nop5, 3b) : "=r"(faulted) : "0" (faulted)); switch (faulted) { case 0: pr_info("converting mcount calls to 0f 1f 44 00 00\n"); memcpy(ftrace_nop, ftrace_test_p6nop, MCOUNT_INSN_SIZE); break; case 1: pr_info("converting mcount calls to 66 66 66 66 90\n"); memcpy(ftrace_nop, ftrace_test_nop5, MCOUNT_INSN_SIZE); break; case 2: pr_info("converting mcount calls to jmp . + 5\n"); memcpy(ftrace_nop, ftrace_test_jmp, MCOUNT_INSN_SIZE); break; } /* 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 */