diff options
Diffstat (limited to 'arch/x86/kernel/ftrace.c')
| -rw-r--r-- | arch/x86/kernel/ftrace.c | 102 |
1 files changed, 95 insertions, 7 deletions
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 32ff36596ab..c3a7cb4bf6e 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -100,7 +100,7 @@ static const unsigned char *ftrace_nop_replace(void) } static int -ftrace_modify_code(unsigned long ip, unsigned const char *old_code, +ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code, unsigned const char *new_code) { unsigned char replaced[MCOUNT_INSN_SIZE]; @@ -141,7 +141,20 @@ int ftrace_make_nop(struct module *mod, old = ftrace_call_replace(ip, addr); new = ftrace_nop_replace(); - return ftrace_modify_code(rec->ip, old, new); + /* + * On boot up, and when modules are loaded, the MCOUNT_ADDR + * is converted to a nop, and will never become MCOUNT_ADDR + * again. This code is either running before SMP (on boot up) + * or before the code will ever be executed (module load). + * We do not want to use the breakpoint version in this case, + * just modify the code directly. + */ + if (addr == MCOUNT_ADDR) + return ftrace_modify_code_direct(rec->ip, old, new); + + /* Normal cases use add_brk_on_nop */ + WARN_ONCE(1, "invalid use of ftrace_make_nop"); + return -EINVAL; } int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) @@ -152,9 +165,47 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) old = ftrace_nop_replace(); new = ftrace_call_replace(ip, addr); - return ftrace_modify_code(rec->ip, old, new); + /* Should only be called when module is loaded */ + return ftrace_modify_code_direct(rec->ip, old, new); } +/* + * The modifying_ftrace_code is used to tell the breakpoint + * handler to call ftrace_int3_handler(). If it fails to + * call this handler for a breakpoint added by ftrace, then + * the kernel may crash. + * + * As atomic_writes on x86 do not need a barrier, we do not + * need to add smp_mb()s for this to work. It is also considered + * that we can not read the modifying_ftrace_code before + * executing the breakpoint. That would be quite remarkable if + * it could do that. Here's the flow that is required: + * + * CPU-0 CPU-1 + * + * atomic_inc(mfc); + * write int3s + * <trap-int3> // implicit (r)mb + * if (atomic_read(mfc)) + * call ftrace_int3_handler() + * + * Then when we are finished: + * + * atomic_dec(mfc); + * + * If we hit a breakpoint that was not set by ftrace, it does not + * matter if ftrace_int3_handler() is called or not. It will + * simply be ignored. But it is crucial that a ftrace nop/caller + * breakpoint is handled. No other user should ever place a + * breakpoint on an ftrace nop/caller location. It must only + * be done by this code. + */ +atomic_t modifying_ftrace_code __read_mostly; + +static int +ftrace_modify_code(unsigned long ip, unsigned const char *old_code, + unsigned const char *new_code); + int ftrace_update_ftrace_func(ftrace_func_t func) { unsigned long ip = (unsigned long)(&ftrace_call); @@ -163,13 +214,17 @@ int ftrace_update_ftrace_func(ftrace_func_t func) memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE); new = ftrace_call_replace(ip, (unsigned long)func); + + /* See comment above by declaration of modifying_ftrace_code */ + atomic_inc(&modifying_ftrace_code); + ret = ftrace_modify_code(ip, old, new); + atomic_dec(&modifying_ftrace_code); + return ret; } -int modifying_ftrace_code __read_mostly; - /* * A breakpoint was added to the code address we are about to * modify, and this is the handle that will just skip over it. @@ -489,13 +544,46 @@ void ftrace_replace_code(int enable) } } +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) { - modifying_ftrace_code++; + /* See comment above by declaration of modifying_ftrace_code */ + atomic_inc(&modifying_ftrace_code); ftrace_modify_all_code(command); - modifying_ftrace_code--; + atomic_dec(&modifying_ftrace_code); } int __init ftrace_dyn_arch_init(void *data) |