![Steven Rostedt](/assets/img/avatar_default.png)
On boot up and module load, it is fine to modify the code directly, without the use of breakpoints. This is because boot up modification is done before SMP is initialized, thus the modification is serial, and module load is done before the module executes. But after that we must use a SMP safe method to modify running code. Otherwise, if we are running the function tracer and update its function (by starting off the stack tracer, or perf tracing) the change of the function called by the ftrace trampoline is done directly. If this is being executed on another CPU, that CPU may take a GPF and crash the kernel. The breakpoint method is used to change the nops at all the functions, but the change of the ftrace callback handler itself was still using a direct modification. If tracing was enabled and the function callback was changed then another CPU could fault if it was currently calling the original callback. This modification must use the breakpoint method too. Note, the direct method is still used for boot up and module load. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
708 lines
16 KiB
C
708 lines
16 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 <linux/module.h>
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#include <trace/syscall.h>
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#include <asm/cacheflush.h>
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#include <asm/kprobes.h>
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#include <asm/ftrace.h>
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#include <asm/nops.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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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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set_all_modules_text_rw();
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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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set_all_modules_text_ro();
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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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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, const 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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return probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE);
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}
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static const unsigned char *ftrace_nop_replace(void)
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{
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return ideal_nops[NOP_ATOMIC5];
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}
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static int
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ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
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unsigned const 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 const 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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/*
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* On boot up, and when modules are loaded, the MCOUNT_ADDR
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* is converted to a nop, and will never become MCOUNT_ADDR
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* again. This code is either running before SMP (on boot up)
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* or before the code will ever be executed (module load).
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* We do not want to use the breakpoint version in this case,
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* just modify the code directly.
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*/
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if (addr == MCOUNT_ADDR)
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return ftrace_modify_code_direct(rec->ip, old, new);
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/* Normal cases use add_brk_on_nop */
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WARN_ONCE(1, "invalid use of ftrace_make_nop");
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return -EINVAL;
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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 const 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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/* Should only be called when module is loaded */
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return ftrace_modify_code_direct(rec->ip, old, new);
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}
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/*
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* The modifying_ftrace_code is used to tell the breakpoint
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* handler to call ftrace_int3_handler(). If it fails to
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* call this handler for a breakpoint added by ftrace, then
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* the kernel may crash.
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*
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* As atomic_writes on x86 do not need a barrier, we do not
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* need to add smp_mb()s for this to work. It is also considered
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* that we can not read the modifying_ftrace_code before
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* executing the breakpoint. That would be quite remarkable if
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* it could do that. Here's the flow that is required:
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*
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* CPU-0 CPU-1
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*
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* atomic_inc(mfc);
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* write int3s
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* <trap-int3> // implicit (r)mb
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* if (atomic_read(mfc))
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* call ftrace_int3_handler()
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*
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* Then when we are finished:
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*
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* atomic_dec(mfc);
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*
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* If we hit a breakpoint that was not set by ftrace, it does not
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* matter if ftrace_int3_handler() is called or not. It will
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* simply be ignored. But it is crucial that a ftrace nop/caller
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* breakpoint is handled. No other user should ever place a
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* breakpoint on an ftrace nop/caller location. It must only
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* be done by this code.
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*/
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atomic_t modifying_ftrace_code __read_mostly;
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static int
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ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
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unsigned const char *new_code);
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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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/* See comment above by declaration of modifying_ftrace_code */
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atomic_inc(&modifying_ftrace_code);
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ret = ftrace_modify_code(ip, old, new);
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atomic_dec(&modifying_ftrace_code);
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return ret;
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}
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/*
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* A breakpoint was added to the code address we are about to
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* modify, and this is the handle that will just skip over it.
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* We are either changing a nop into a trace call, or a trace
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* call to a nop. While the change is taking place, we treat
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* it just like it was a nop.
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*/
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int ftrace_int3_handler(struct pt_regs *regs)
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{
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if (WARN_ON_ONCE(!regs))
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return 0;
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if (!ftrace_location(regs->ip - 1))
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return 0;
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regs->ip += MCOUNT_INSN_SIZE - 1;
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return 1;
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}
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static int ftrace_write(unsigned long ip, const char *val, int size)
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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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return probe_kernel_write((void *)ip, val, size);
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}
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static int add_break(unsigned long ip, const char *old)
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{
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unsigned char replaced[MCOUNT_INSN_SIZE];
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unsigned char brk = BREAKPOINT_INSTRUCTION;
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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, MCOUNT_INSN_SIZE) != 0)
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return -EINVAL;
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if (ftrace_write(ip, &brk, 1))
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return -EPERM;
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return 0;
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}
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static int add_brk_on_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned const char *old;
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unsigned long ip = rec->ip;
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old = ftrace_call_replace(ip, addr);
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return add_break(rec->ip, old);
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}
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static int add_brk_on_nop(struct dyn_ftrace *rec)
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{
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unsigned const char *old;
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old = ftrace_nop_replace();
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return add_break(rec->ip, old);
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}
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static int add_breakpoints(struct dyn_ftrace *rec, int enable)
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{
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unsigned long ftrace_addr;
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int ret;
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ret = ftrace_test_record(rec, enable);
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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switch (ret) {
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case FTRACE_UPDATE_IGNORE:
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return 0;
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case FTRACE_UPDATE_MAKE_CALL:
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/* converting nop to call */
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return add_brk_on_nop(rec);
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case FTRACE_UPDATE_MAKE_NOP:
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/* converting a call to a nop */
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return add_brk_on_call(rec, ftrace_addr);
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}
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return 0;
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}
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/*
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* On error, we need to remove breakpoints. This needs to
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* be done caefully. If the address does not currently have a
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* breakpoint, we know we are done. Otherwise, we look at the
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* remaining 4 bytes of the instruction. If it matches a nop
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* we replace the breakpoint with the nop. Otherwise we replace
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* it with the call instruction.
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*/
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static int remove_breakpoint(struct dyn_ftrace *rec)
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{
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unsigned char ins[MCOUNT_INSN_SIZE];
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unsigned char brk = BREAKPOINT_INSTRUCTION;
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const unsigned char *nop;
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unsigned long ftrace_addr;
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unsigned long ip = rec->ip;
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/* If we fail the read, just give up */
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if (probe_kernel_read(ins, (void *)ip, MCOUNT_INSN_SIZE))
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return -EFAULT;
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/* If this does not have a breakpoint, we are done */
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if (ins[0] != brk)
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return -1;
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nop = ftrace_nop_replace();
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/*
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* If the last 4 bytes of the instruction do not match
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* a nop, then we assume that this is a call to ftrace_addr.
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*/
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if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0) {
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/*
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* For extra paranoidism, we check if the breakpoint is on
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* a call that would actually jump to the ftrace_addr.
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* If not, don't touch the breakpoint, we make just create
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* a disaster.
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*/
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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nop = ftrace_call_replace(ip, ftrace_addr);
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if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
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return -EINVAL;
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}
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return probe_kernel_write((void *)ip, &nop[0], 1);
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}
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static int add_update_code(unsigned long ip, unsigned const char *new)
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{
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/* skip breakpoint */
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ip++;
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new++;
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if (ftrace_write(ip, new, MCOUNT_INSN_SIZE - 1))
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return -EPERM;
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return 0;
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}
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static int add_update_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_call_replace(ip, addr);
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return add_update_code(ip, new);
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}
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static int add_update_nop(struct dyn_ftrace *rec)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_nop_replace();
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return add_update_code(ip, new);
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}
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static int add_update(struct dyn_ftrace *rec, int enable)
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{
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unsigned long ftrace_addr;
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int ret;
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ret = ftrace_test_record(rec, enable);
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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switch (ret) {
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case FTRACE_UPDATE_IGNORE:
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return 0;
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case FTRACE_UPDATE_MAKE_CALL:
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/* converting nop to call */
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return add_update_call(rec, ftrace_addr);
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case FTRACE_UPDATE_MAKE_NOP:
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/* converting a call to a nop */
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return add_update_nop(rec);
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}
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return 0;
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}
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static int finish_update_call(struct dyn_ftrace *rec, unsigned long addr)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_call_replace(ip, addr);
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if (ftrace_write(ip, new, 1))
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return -EPERM;
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return 0;
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}
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static int finish_update_nop(struct dyn_ftrace *rec)
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{
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unsigned long ip = rec->ip;
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unsigned const char *new;
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new = ftrace_nop_replace();
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if (ftrace_write(ip, new, 1))
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return -EPERM;
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return 0;
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}
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static int finish_update(struct dyn_ftrace *rec, int enable)
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{
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unsigned long ftrace_addr;
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int ret;
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ret = ftrace_update_record(rec, enable);
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ftrace_addr = (unsigned long)FTRACE_ADDR;
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switch (ret) {
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case FTRACE_UPDATE_IGNORE:
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return 0;
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case FTRACE_UPDATE_MAKE_CALL:
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/* converting nop to call */
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return finish_update_call(rec, ftrace_addr);
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case FTRACE_UPDATE_MAKE_NOP:
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/* converting a call to a nop */
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return finish_update_nop(rec);
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}
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return 0;
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}
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static void do_sync_core(void *data)
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{
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sync_core();
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}
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static void run_sync(void)
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{
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int enable_irqs = irqs_disabled();
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/* We may be called with interrupts disbled (on bootup). */
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if (enable_irqs)
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local_irq_enable();
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on_each_cpu(do_sync_core, NULL, 1);
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if (enable_irqs)
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local_irq_disable();
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}
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void ftrace_replace_code(int enable)
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{
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struct ftrace_rec_iter *iter;
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struct dyn_ftrace *rec;
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const char *report = "adding breakpoints";
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int count = 0;
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int ret;
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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ret = add_breakpoints(rec, enable);
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if (ret)
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goto remove_breakpoints;
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count++;
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}
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run_sync();
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report = "updating code";
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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ret = add_update(rec, enable);
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if (ret)
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goto remove_breakpoints;
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}
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run_sync();
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report = "removing breakpoints";
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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ret = finish_update(rec, enable);
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if (ret)
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goto remove_breakpoints;
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}
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run_sync();
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return;
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remove_breakpoints:
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ftrace_bug(ret, rec ? rec->ip : 0);
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printk(KERN_WARNING "Failed on %s (%d):\n", report, count);
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for_ftrace_rec_iter(iter) {
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rec = ftrace_rec_iter_record(iter);
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remove_breakpoint(rec);
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}
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}
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static int
|
|
ftrace_modify_code(unsigned long ip, unsigned const char *old_code,
|
|
unsigned const char *new_code)
|
|
{
|
|
int ret;
|
|
|
|
ret = add_break(ip, old_code);
|
|
if (ret)
|
|
goto out;
|
|
|
|
run_sync();
|
|
|
|
ret = add_update_code(ip, new_code);
|
|
if (ret)
|
|
goto fail_update;
|
|
|
|
run_sync();
|
|
|
|
ret = ftrace_write(ip, new_code, 1);
|
|
if (ret) {
|
|
ret = -EPERM;
|
|
goto out;
|
|
}
|
|
run_sync();
|
|
out:
|
|
return ret;
|
|
|
|
fail_update:
|
|
probe_kernel_write((void *)ip, &old_code[0], 1);
|
|
goto out;
|
|
}
|
|
|
|
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(¤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;
|
|
}
|
|
|
|
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 */
|