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be0f272bfc
When building the arm64 kernel with both CONFIG_ARM64_MODULE_PLTS and CONFIG_DYNAMIC_FTRACE enabled, the ftrace-mod.o object file is built with the kernel and contains a trampoline that is linked into each module, so that modules can be loaded far away from the kernel and still reach the ftrace entry point in the core kernel with an ordinary relative branch, as is emitted by the compiler instrumentation code dynamic ftrace relies on. In order to be able to build out of tree modules, this object file needs to be included into the linux-headers or linux-devel packages, which is undesirable, as it makes arm64 a special case (although a precedent does exist for 32-bit PPC). Given that the trampoline essentially consists of a PLT entry, let's not bother with a source or object file for it, and simply patch it in whenever the trampoline is being populated, using the existing PLT support routines. Cc: <stable@vger.kernel.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
279 lines
7.3 KiB
C
279 lines
7.3 KiB
C
/*
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* arch/arm64/kernel/ftrace.c
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*
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* Copyright (C) 2013 Linaro Limited
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* Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/ftrace.h>
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#include <linux/module.h>
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#include <linux/swab.h>
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#include <linux/uaccess.h>
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#include <asm/cacheflush.h>
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#include <asm/debug-monitors.h>
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#include <asm/ftrace.h>
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#include <asm/insn.h>
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#ifdef CONFIG_DYNAMIC_FTRACE
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/*
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* Replace a single instruction, which may be a branch or NOP.
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* If @validate == true, a replaced instruction is checked against 'old'.
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*/
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static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
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bool validate)
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{
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u32 replaced;
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/*
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* Note:
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* We are paranoid about modifying text, as if a bug were to happen, it
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* could cause us to read or write to someplace that could cause harm.
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* Carefully read and modify the code with aarch64_insn_*() which uses
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* probe_kernel_*(), and make sure what we read is what we expected it
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* to be before modifying it.
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*/
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if (validate) {
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if (aarch64_insn_read((void *)pc, &replaced))
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return -EFAULT;
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if (replaced != old)
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return -EINVAL;
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}
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if (aarch64_insn_patch_text_nosync((void *)pc, new))
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return -EPERM;
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return 0;
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}
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/*
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* Replace tracer function in ftrace_caller()
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*/
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int ftrace_update_ftrace_func(ftrace_func_t func)
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{
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unsigned long pc;
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u32 new;
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pc = (unsigned long)&ftrace_call;
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new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
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AARCH64_INSN_BRANCH_LINK);
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return ftrace_modify_code(pc, 0, new, false);
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}
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/*
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* Turn on the call to ftrace_caller() in instrumented function
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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 long pc = rec->ip;
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u32 old, new;
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long offset = (long)pc - (long)addr;
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if (offset < -SZ_128M || offset >= SZ_128M) {
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#ifdef CONFIG_ARM64_MODULE_PLTS
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struct plt_entry trampoline;
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struct module *mod;
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/*
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* On kernels that support module PLTs, the offset between the
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* branch instruction and its target may legally exceed the
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* range of an ordinary relative 'bl' opcode. In this case, we
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* need to branch via a trampoline in the module.
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*
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* NOTE: __module_text_address() must be called with preemption
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* disabled, but we can rely on ftrace_lock to ensure that 'mod'
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* retains its validity throughout the remainder of this code.
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*/
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preempt_disable();
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mod = __module_text_address(pc);
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preempt_enable();
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if (WARN_ON(!mod))
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return -EINVAL;
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/*
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* There is only one ftrace trampoline per module. For now,
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* this is not a problem since on arm64, all dynamic ftrace
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* invocations are routed via ftrace_caller(). This will need
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* to be revisited if support for multiple ftrace entry points
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* is added in the future, but for now, the pr_err() below
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* deals with a theoretical issue only.
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*/
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trampoline = get_plt_entry(addr);
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if (!plt_entries_equal(mod->arch.ftrace_trampoline,
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&trampoline)) {
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if (!plt_entries_equal(mod->arch.ftrace_trampoline,
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&(struct plt_entry){})) {
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pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
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return -EINVAL;
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}
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/* point the trampoline to our ftrace entry point */
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module_disable_ro(mod);
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*mod->arch.ftrace_trampoline = trampoline;
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module_enable_ro(mod, true);
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/* update trampoline before patching in the branch */
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smp_wmb();
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}
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addr = (unsigned long)(void *)mod->arch.ftrace_trampoline;
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#else /* CONFIG_ARM64_MODULE_PLTS */
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return -EINVAL;
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#endif /* CONFIG_ARM64_MODULE_PLTS */
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}
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old = aarch64_insn_gen_nop();
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new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
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return ftrace_modify_code(pc, old, new, true);
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}
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/*
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* Turn off the call to ftrace_caller() in instrumented function
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*/
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int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
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unsigned long addr)
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{
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unsigned long pc = rec->ip;
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bool validate = true;
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u32 old = 0, new;
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long offset = (long)pc - (long)addr;
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if (offset < -SZ_128M || offset >= SZ_128M) {
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#ifdef CONFIG_ARM64_MODULE_PLTS
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u32 replaced;
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/*
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* 'mod' is only set at module load time, but if we end up
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* dealing with an out-of-range condition, we can assume it
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* is due to a module being loaded far away from the kernel.
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*/
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if (!mod) {
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preempt_disable();
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mod = __module_text_address(pc);
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preempt_enable();
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if (WARN_ON(!mod))
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return -EINVAL;
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}
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/*
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* The instruction we are about to patch may be a branch and
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* link instruction that was redirected via a PLT entry. In
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* this case, the normal validation will fail, but we can at
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* least check that we are dealing with a branch and link
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* instruction that points into the right module.
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*/
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if (aarch64_insn_read((void *)pc, &replaced))
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return -EFAULT;
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if (!aarch64_insn_is_bl(replaced) ||
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!within_module(pc + aarch64_get_branch_offset(replaced),
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mod))
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return -EINVAL;
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validate = false;
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#else /* CONFIG_ARM64_MODULE_PLTS */
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return -EINVAL;
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#endif /* CONFIG_ARM64_MODULE_PLTS */
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} else {
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old = aarch64_insn_gen_branch_imm(pc, addr,
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AARCH64_INSN_BRANCH_LINK);
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}
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new = aarch64_insn_gen_nop();
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return ftrace_modify_code(pc, old, new, validate);
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}
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void arch_ftrace_update_code(int command)
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{
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ftrace_modify_all_code(command);
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}
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int __init ftrace_dyn_arch_init(void)
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{
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return 0;
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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/*
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* function_graph tracer expects ftrace_return_to_handler() to be called
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* on the way back to parent. For this purpose, this function is called
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* in _mcount() or ftrace_caller() to replace return address (*parent) on
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* the call stack to return_to_handler.
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*
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* Note that @frame_pointer is used only for sanity check later.
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*/
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void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
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unsigned long frame_pointer)
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{
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unsigned long return_hooker = (unsigned long)&return_to_handler;
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unsigned long old;
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struct ftrace_graph_ent trace;
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int err;
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if (unlikely(atomic_read(¤t->tracing_graph_pause)))
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return;
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/*
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* Note:
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* No protection against faulting at *parent, which may be seen
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* on other archs. It's unlikely on AArch64.
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*/
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old = *parent;
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trace.func = self_addr;
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trace.depth = current->curr_ret_stack + 1;
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/* Only trace if the calling function expects to */
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if (!ftrace_graph_entry(&trace))
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return;
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err = ftrace_push_return_trace(old, self_addr, &trace.depth,
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frame_pointer, NULL);
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if (err == -EBUSY)
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return;
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else
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*parent = return_hooker;
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}
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#ifdef CONFIG_DYNAMIC_FTRACE
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/*
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* Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
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* depending on @enable.
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*/
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static int ftrace_modify_graph_caller(bool enable)
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{
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unsigned long pc = (unsigned long)&ftrace_graph_call;
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u32 branch, nop;
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branch = aarch64_insn_gen_branch_imm(pc,
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(unsigned long)ftrace_graph_caller,
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AARCH64_INSN_BRANCH_NOLINK);
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nop = aarch64_insn_gen_nop();
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if (enable)
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return ftrace_modify_code(pc, nop, branch, true);
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else
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return ftrace_modify_code(pc, branch, nop, true);
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}
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int ftrace_enable_ftrace_graph_caller(void)
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{
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return ftrace_modify_graph_caller(true);
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}
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int ftrace_disable_ftrace_graph_caller(void)
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{
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return ftrace_modify_graph_caller(false);
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}
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#endif /* CONFIG_DYNAMIC_FTRACE */
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#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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