From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Mon, 10 Apr 2017 15:13:42 +0100 Subject: [PATCH 1/2] arm64: ftrace: don't validate branch via PLT in ftrace_make_nop() In-Reply-To: <20170410141343.1045-1-ard.biesheuvel@linaro.org> References: <20170410141343.1045-1-ard.biesheuvel@linaro.org> Message-ID: <20170410141343.1045-2-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 in this case if CONFIG_ARM64_MODULE_PLTS is configured. Signed-off-by: Ard Biesheuvel --- arch/arm64/kernel/ftrace.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index 40ad08ac569a..a8db6857cad6 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -84,12 +84,15 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr) { unsigned long pc = rec->ip; - u32 old, new; + u32 old = 0, new; - old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); + if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) + 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, + !IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)); } void arch_ftrace_update_code(int command) -- 2.9.3