4.14-stable review patch. If anyone has any objections, please let me know.
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From: Ard Biesheuvel ard.biesheuvel@linaro.org
commit be0f272bfc83797f70d44faca86954df62e2bbc0 upstream.
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.
Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arm64/Makefile | 3 --- arch/arm64/include/asm/module.h | 2 +- arch/arm64/kernel/Makefile | 3 --- arch/arm64/kernel/ftrace-mod.S | 18 ------------------ arch/arm64/kernel/ftrace.c | 14 ++++++++------ arch/arm64/kernel/module-plts.c | 12 ++++++++++++ arch/arm64/kernel/module.lds | 1 + 7 files changed, 22 insertions(+), 31 deletions(-)
--- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -77,9 +77,6 @@ endif
ifeq ($(CONFIG_ARM64_MODULE_PLTS),y) KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/arm64/kernel/module.lds -ifeq ($(CONFIG_DYNAMIC_FTRACE),y) -KBUILD_LDFLAGS_MODULE += $(objtree)/arch/arm64/kernel/ftrace-mod.o -endif endif
# Default value --- a/arch/arm64/include/asm/module.h +++ b/arch/arm64/include/asm/module.h @@ -32,7 +32,7 @@ struct mod_arch_specific { struct mod_plt_sec init;
/* for CONFIG_DYNAMIC_FTRACE */ - void *ftrace_trampoline; + struct plt_entry *ftrace_trampoline; }; #endif
--- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -63,6 +63,3 @@ extra-y += $(head-y) vmlinux.lds ifeq ($(CONFIG_DEBUG_EFI),y) AFLAGS_head.o += -DVMLINUX_PATH=""$(realpath $(objtree)/vmlinux)"" endif - -# will be included by each individual module but not by the core kernel itself -extra-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o --- a/arch/arm64/kernel/ftrace-mod.S +++ /dev/null @@ -1,18 +0,0 @@ -/* - * Copyright (C) 2017 Linaro Ltd ard.biesheuvel@linaro.org - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License version 2 as - * published by the Free Software Foundation. - */ - -#include <linux/linkage.h> -#include <asm/assembler.h> - - .section ".text.ftrace_trampoline", "ax" - .align 3 -0: .quad 0 -__ftrace_trampoline: - ldr x16, 0b - br x16 -ENDPROC(__ftrace_trampoline) --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -76,7 +76,7 @@ int ftrace_make_call(struct dyn_ftrace *
if (offset < -SZ_128M || offset >= SZ_128M) { #ifdef CONFIG_ARM64_MODULE_PLTS - unsigned long *trampoline; + struct plt_entry trampoline; struct module *mod;
/* @@ -104,22 +104,24 @@ int ftrace_make_call(struct dyn_ftrace * * is added in the future, but for now, the pr_err() below * deals with a theoretical issue only. */ - trampoline = (unsigned long *)mod->arch.ftrace_trampoline; - if (trampoline[0] != addr) { - if (trampoline[0] != 0) { + trampoline = get_plt_entry(addr); + if (!plt_entries_equal(mod->arch.ftrace_trampoline, + &trampoline)) { + if (!plt_entries_equal(mod->arch.ftrace_trampoline, + &(struct plt_entry){})) { pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n"); return -EINVAL; }
/* point the trampoline to our ftrace entry point */ module_disable_ro(mod); - trampoline[0] = addr; + *mod->arch.ftrace_trampoline = trampoline; module_enable_ro(mod, true);
/* update trampoline before patching in the branch */ smp_wmb(); } - addr = (unsigned long)&trampoline[1]; + addr = (unsigned long)(void *)mod->arch.ftrace_trampoline; #else /* CONFIG_ARM64_MODULE_PLTS */ return -EINVAL; #endif /* CONFIG_ARM64_MODULE_PLTS */ --- a/arch/arm64/kernel/module-plts.c +++ b/arch/arm64/kernel/module-plts.c @@ -120,6 +120,7 @@ int module_frob_arch_sections(Elf_Ehdr * unsigned long core_plts = 0; unsigned long init_plts = 0; Elf64_Sym *syms = NULL; + Elf_Shdr *tramp = NULL; int i;
/* @@ -131,6 +132,10 @@ int module_frob_arch_sections(Elf_Ehdr * mod->arch.core.plt = sechdrs + i; else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) mod->arch.init.plt = sechdrs + i; + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && + !strcmp(secstrings + sechdrs[i].sh_name, + ".text.ftrace_trampoline")) + tramp = sechdrs + i; else if (sechdrs[i].sh_type == SHT_SYMTAB) syms = (Elf64_Sym *)sechdrs[i].sh_addr; } @@ -181,5 +186,12 @@ int module_frob_arch_sections(Elf_Ehdr * mod->arch.init.plt_num_entries = 0; mod->arch.init.plt_max_entries = init_plts;
+ if (tramp) { + tramp->sh_type = SHT_NOBITS; + tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + tramp->sh_addralign = __alignof__(struct plt_entry); + tramp->sh_size = sizeof(struct plt_entry); + } + return 0; } --- a/arch/arm64/kernel/module.lds +++ b/arch/arm64/kernel/module.lds @@ -1,4 +1,5 @@ SECTIONS { .plt (NOLOAD) : { BYTE(0) } .init.plt (NOLOAD) : { BYTE(0) } + .text.ftrace_trampoline (NOLOAD) : { BYTE(0) } }