// SPDX-License-Identifier: GPL-2.0-only /* * arch/arm64/kernel/ftrace.c * * Copyright (C) 2013 Linaro Limited * Author: AKASHI Takahiro */ #include #include #include #include #include #include #include #include #ifdef CONFIG_DYNAMIC_FTRACE /* * Replace a single instruction, which may be a branch or NOP. * If @validate == true, a replaced instruction is checked against 'old'. */ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, bool validate) { u32 replaced; /* * Note: * We are paranoid about modifying text, as if a bug were to happen, it * could cause us to read or write to someplace that could cause harm. * Carefully read and modify the code with aarch64_insn_*() which uses * probe_kernel_*(), and make sure what we read is what we expected it * to be before modifying it. */ if (validate) { if (aarch64_insn_read((void *)pc, &replaced)) return -EFAULT; if (replaced != old) return -EINVAL; } if (aarch64_insn_patch_text_nosync((void *)pc, new)) return -EPERM; return 0; } /* * Replace tracer function in ftrace_caller() */ int ftrace_update_ftrace_func(ftrace_func_t func) { unsigned long pc; u32 new; pc = (unsigned long)&ftrace_call; new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, AARCH64_INSN_BRANCH_LINK); return ftrace_modify_code(pc, 0, new, false); } static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr) { #ifdef CONFIG_ARM64_MODULE_PLTS struct plt_entry *plt = mod->arch.ftrace_trampolines; if (addr == FTRACE_ADDR) return &plt[FTRACE_PLT_IDX]; if (addr == FTRACE_REGS_ADDR && IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS)) return &plt[FTRACE_REGS_PLT_IDX]; #endif return NULL; } /* * Find the address the callsite must branch to in order to reach '*addr'. * * Due to the limited range of 'BL' instructions, modules may be placed too far * away to branch directly and must use a PLT. * * Returns true when '*addr' contains a reachable target address, or has been * modified to contain a PLT address. Returns false otherwise. */ static bool ftrace_find_callable_addr(struct dyn_ftrace *rec, struct module *mod, unsigned long *addr) { unsigned long pc = rec->ip; long offset = (long)*addr - (long)pc; struct plt_entry *plt; /* * When the target is within range of the 'BL' instruction, use 'addr' * as-is and branch to that directly. */ if (offset >= -SZ_128M && offset < SZ_128M) return true; /* * When the target is outside of the range of a 'BL' instruction, we * must use a PLT to reach it. We can only place PLTs for modules, and * only when module PLT support is built-in. */ if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) return false; /* * 'mod' is only set at module load time, but if we end up * dealing with an out-of-range condition, we can assume it * is due to a module being loaded far away from the kernel. * * NOTE: __module_text_address() must be called with preemption * disabled, but we can rely on ftrace_lock to ensure that 'mod' * retains its validity throughout the remainder of this code. */ if (!mod) { preempt_disable(); mod = __module_text_address(pc); preempt_enable(); } if (WARN_ON(!mod)) return false; plt = get_ftrace_plt(mod, *addr); if (!plt) { pr_err("ftrace: no module PLT for %ps\n", (void *)*addr); return false; } *addr = (unsigned long)plt; return true; } /* * Turn on the call to ftrace_caller() in instrumented function */ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) { unsigned long pc = rec->ip; u32 old, new; if (!ftrace_find_callable_addr(rec, NULL, &addr)) return -EINVAL; old = aarch64_insn_gen_nop(); new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); return ftrace_modify_code(pc, old, new, true); } #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, unsigned long addr) { unsigned long pc = rec->ip; u32 old, new; if (!ftrace_find_callable_addr(rec, NULL, &old_addr)) return -EINVAL; if (!ftrace_find_callable_addr(rec, NULL, &addr)) return -EINVAL; old = aarch64_insn_gen_branch_imm(pc, old_addr, AARCH64_INSN_BRANCH_LINK); new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); return ftrace_modify_code(pc, old, new, true); } /* * The compiler has inserted two NOPs before the regular function prologue. * All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live, * and x9-x18 are free for our use. * * At runtime we want to be able to swing a single NOP <-> BL to enable or * disable the ftrace call. The BL requires us to save the original LR value, * so here we insert a over the first NOP so the instructions * before the regular prologue are: * * | Compiled | Disabled | Enabled | * +----------+------------+------------+ * | NOP | MOV X9, LR | MOV X9, LR | * | NOP | NOP | BL | * * The LR value will be recovered by ftrace_regs_entry, and restored into LR * before returning to the regular function prologue. When a function is not * being traced, the MOV is not harmful given x9 is not live per the AAPCS. * * Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address of * the BL. */ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) { unsigned long pc = rec->ip - AARCH64_INSN_SIZE; u32 old, new; old = aarch64_insn_gen_nop(); new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9, AARCH64_INSN_REG_LR, AARCH64_INSN_VARIANT_64BIT); return ftrace_modify_code(pc, old, new, true); } #endif /* * Turn off the call to ftrace_caller() in instrumented function */ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { unsigned long pc = rec->ip; u32 old = 0, new; new = aarch64_insn_gen_nop(); /* * When using mcount, callsites in modules may have been initalized to * call an arbitrary module PLT (which redirects to the _mcount stub) * rather than the ftrace PLT we'll use at runtime (which redirects to * the ftrace trampoline). We can ignore the old PLT when initializing * the callsite. * * Note: 'mod' is only set at module load time. */ if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && mod) { return aarch64_insn_patch_text_nosync((void *)pc, new); } if (!ftrace_find_callable_addr(rec, mod, &addr)) return -EINVAL; old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); return ftrace_modify_code(pc, old, new, true); } void arch_ftrace_update_code(int command) { command |= FTRACE_MAY_SLEEP; ftrace_modify_all_code(command); } int __init ftrace_dyn_arch_init(void) { return 0; } #endif /* CONFIG_DYNAMIC_FTRACE */ #ifdef CONFIG_FUNCTION_GRAPH_TRACER /* * function_graph tracer expects ftrace_return_to_handler() to be called * on the way back to parent. For this purpose, this function is called * in _mcount() or ftrace_caller() to replace return address (*parent) on * the call stack to return_to_handler. * * Note that @frame_pointer is used only for sanity check later. */ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, unsigned long frame_pointer) { unsigned long return_hooker = (unsigned long)&return_to_handler; unsigned long old; if (unlikely(atomic_read(¤t->tracing_graph_pause))) return; /* * Note: * No protection against faulting at *parent, which may be seen * on other archs. It's unlikely on AArch64. */ old = *parent; if (!function_graph_enter(old, self_addr, frame_pointer, NULL)) *parent = return_hooker; } #ifdef CONFIG_DYNAMIC_FTRACE /* * Turn on/off the call to ftrace_graph_caller() in ftrace_caller() * depending on @enable. */ static int ftrace_modify_graph_caller(bool enable) { unsigned long pc = (unsigned long)&ftrace_graph_call; u32 branch, nop; branch = aarch64_insn_gen_branch_imm(pc, (unsigned long)ftrace_graph_caller, AARCH64_INSN_BRANCH_NOLINK); nop = aarch64_insn_gen_nop(); if (enable) return ftrace_modify_code(pc, nop, branch, true); else return ftrace_modify_code(pc, branch, nop, true); } int ftrace_enable_ftrace_graph_caller(void) { return ftrace_modify_graph_caller(true); } int ftrace_disable_ftrace_graph_caller(void) { return ftrace_modify_graph_caller(false); } #endif /* CONFIG_DYNAMIC_FTRACE */ #endif /* CONFIG_FUNCTION_GRAPH_TRACER */