| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * arch/arm64/kernel/ftrace.c |
| * |
| * Copyright (C) 2013 Linaro Limited |
| * Author: AKASHI Takahiro <takahiro.akashi@linaro.org> |
| */ |
| |
| #include <linux/ftrace.h> |
| #include <linux/module.h> |
| #include <linux/swab.h> |
| #include <linux/uaccess.h> |
| |
| #include <asm/cacheflush.h> |
| #include <asm/debug-monitors.h> |
| #include <asm/ftrace.h> |
| #include <asm/insn.h> |
| #include <asm/patching.h> |
| |
| #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)function_nocfi(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 <MOV X9, LR> 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 <entry> | |
| * |
| * 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; |
| |
| if (!ftrace_find_callable_addr(rec, mod, &addr)) |
| return -EINVAL; |
| |
| old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); |
| new = aarch64_insn_gen_nop(); |
| |
| return ftrace_modify_code(pc, old, new, true); |
| } |
| |
| void arch_ftrace_update_code(int command) |
| { |
| command |= FTRACE_MAY_SLEEP; |
| ftrace_modify_all_code(command); |
| } |
| #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. |
| */ |
| 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, |
| (void *)frame_pointer)) { |
| *parent = return_hooker; |
| } |
| } |
| |
| #ifdef CONFIG_DYNAMIC_FTRACE |
| |
| #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS |
| void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, |
| struct ftrace_ops *op, struct ftrace_regs *fregs) |
| { |
| /* |
| * When DYNAMIC_FTRACE_WITH_REGS is selected, `fregs` can never be NULL |
| * and arch_ftrace_get_regs(fregs) will always give a non-NULL pt_regs |
| * in which we can safely modify the LR. |
| */ |
| struct pt_regs *regs = arch_ftrace_get_regs(fregs); |
| unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs); |
| |
| prepare_ftrace_return(ip, parent, frame_pointer(regs)); |
| } |
| #else |
| /* |
| * 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_WITH_REGS */ |
| #endif /* CONFIG_DYNAMIC_FTRACE */ |
| #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ |