From f8af0b364e249eef0c71200826563947cd74267e Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 6 Jun 2017 17:00:21 +0000 Subject: arm64: ftrace: don't validate branch via PLT in ftrace_make_nop() When turning branch instructions into NOPs, we attempt to validate the action by comparing the old value at the call site with the opcode of a direct relative branch instruction pointing at the old target. However, these call sites are statically initialized to call _mcount(), and may be redirected via a PLT entry if the module is loaded far away from the kernel text, leading to false negatives and spurious errors. So skip the validation if CONFIG_ARM64_MODULE_PLTS is configured. Signed-off-by: Ard Biesheuvel Signed-off-by: Will Deacon --- arch/arm64/kernel/ftrace.c | 46 +++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 43 insertions(+), 3 deletions(-) (limited to 'arch/arm64/kernel/ftrace.c') diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index 40ad08ac569a..4cb576374b82 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -84,12 +84,52 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { unsigned long pc = rec->ip; - u32 old, new; + long offset = (long)pc - (long)addr; + bool validate = true; + u32 old = 0, new; + + if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && + (offset < -SZ_128M || offset >= SZ_128M)) { + u32 replaced; + + /* + * '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. + */ + if (!mod) { + preempt_disable(); + mod = __module_text_address(pc); + preempt_enable(); + + if (WARN_ON(!mod)) + return -EINVAL; + } + + /* + * The instruction we are about to patch may be a branch and + * link instruction that was redirected via a PLT entry. In + * this case, the normal validation will fail, but we can at + * least check that we are dealing with a branch and link + * instruction that points into the right module. + */ + if (aarch64_insn_read((void *)pc, &replaced)) + return -EFAULT; + + if (!aarch64_insn_is_bl(replaced) || + !within_module(pc + aarch64_get_branch_offset(replaced), + mod)) + return -EINVAL; + + validate = false; + } else { + old = aarch64_insn_gen_branch_imm(pc, addr, + AARCH64_INSN_BRANCH_LINK); + } - 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); + return ftrace_modify_code(pc, old, new, validate); } void arch_ftrace_update_code(int command) -- cgit v1.2.3