| Message ID | 20170410141343.1045-3-ard.biesheuvel@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 10 April 2017 at 15:13, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > Currently, dynamic ftrace support in the arm64 kernel assumes that all > core kernel code is within range of ordinary branch instructions in > module code, which is usually the case, but is no longer guaranteed now > that we have support for module PLTs and address space randomization. > > Since all patching of branch instructions involves function calls to > ftrace_caller(), we can emit the modules with a trampoline that has > unlimited range, and patch the branch instruction to call the trampoline > if ftrace_caller() itself is out of range. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm64/Kconfig | 2 +- > arch/arm64/Makefile | 3 ++ > arch/arm64/include/asm/module.h | 3 ++ > arch/arm64/kernel/ftrace.c | 37 ++++++++++++++++++-- > arch/arm64/kernel/module-plts.c | 10 ++++++ > arch/arm64/lib/Makefile | 2 ++ > arch/arm64/lib/ftrace-mod.S | 25 +++++++++++++ > 7 files changed, 78 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index e7f043efff41..31af7ea72072 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -982,7 +982,7 @@ config RANDOMIZE_BASE > > config RANDOMIZE_MODULE_REGION_FULL > bool "Randomize the module region independently from the core kernel" > - depends on RANDOMIZE_BASE && !DYNAMIC_FTRACE > + depends on RANDOMIZE_BASE > default y > help > Randomizes the location of the module region without considering the > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index b9a4a934ca05..01498eab5ada 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -68,6 +68,9 @@ 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/lib/ftrace-mod.o > +endif > endif > > # Default value > diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h > index e12af6754634..2ff2b7782957 100644 > --- a/arch/arm64/include/asm/module.h > +++ b/arch/arm64/include/asm/module.h > @@ -25,6 +25,9 @@ struct mod_arch_specific { > struct elf64_shdr *plt; > int plt_num_entries; > int plt_max_entries; > + > + /* for CONFIG_DYNAMIC_FTRACE */ > + struct elf64_shdr *ftrace_trampoline; > }; > #endif > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index a8db6857cad6..8f5a7dc36c1b 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -9,11 +9,14 @@ > * published by the Free Software Foundation. > */ > > +#include <linux/elf.h> > #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> > > @@ -63,6 +66,35 @@ int ftrace_update_ftrace_func(ftrace_func_t func) > return ftrace_modify_code(pc, 0, new, false); > } > > +#ifdef CONFIG_ARM64_MODULE_PLTS > +EXPORT_SYMBOL_GPL(ftrace_caller); > +#endif > + > +static u32 __ftrace_gen_branch(unsigned long pc, unsigned long addr) > +{ > + long offset = (long)pc - (long)addr; > + struct module *mod; > + > + if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && > + addr == (unsigned long)&ftrace_caller && > + unlikely(offset < -SZ_128M || offset >= SZ_128M)) { > + > + /* > + * On kernels that support module PLTs, the offset between the > + * call and its target may legally exceed the range of an > + * ordinary branch instruction. In this case, we need to branch > + * via a trampoline in the module. > + */ > + mod = __module_address(pc); > + if (WARN_ON(!mod)) > + return AARCH64_BREAK_FAULT; > + > + addr = (unsigned long)mod->arch.ftrace_trampoline->sh_addr; > + } > + > + return aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); > +} > + > /* > * Turn on the call to ftrace_caller() in instrumented function > */ > @@ -72,7 +104,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) > u32 old, new; > > old = aarch64_insn_gen_nop(); > - new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); > + new = __ftrace_gen_branch(pc, addr); > > return ftrace_modify_code(pc, old, new, true); > } > @@ -87,8 +119,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, > u32 old = 0, new; > > if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) > - old = aarch64_insn_gen_branch_imm(pc, addr, > - AARCH64_INSN_BRANCH_LINK); > + old = __ftrace_gen_branch(pc, addr); > new = aarch64_insn_gen_nop(); > > return ftrace_modify_code(pc, old, new, > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > index 1ce90d8450ae..859c7170e69a 100644 > --- a/arch/arm64/kernel/module-plts.c > +++ b/arch/arm64/kernel/module-plts.c > @@ -162,6 +162,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > mod->arch.plt = sechdrs + i; > else if (sechdrs[i].sh_type == SHT_SYMTAB) > syms = (Elf64_Sym *)sechdrs[i].sh_addr; > + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && > + strcmp(".text.ftrace_trampoline", > + secstrings + sechdrs[i].sh_name) == 0) > + mod->arch.ftrace_trampoline = sechdrs + i; > } > > if (!mod->arch.plt) { > @@ -173,6 +177,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > return -ENOEXEC; > } > > + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && !mod->arch.ftrace_trampoline) { > + pr_err("%s: module ftrace trampoline section missing\n", > + mod->name); > + return -ENOEXEC; > + } > + > for (i = 0; i < ehdr->e_shnum; i++) { > Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; > int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); > diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile > index c86b7909ef31..b01dcfa9c002 100644 > --- a/arch/arm64/lib/Makefile > +++ b/arch/arm64/lib/Makefile > @@ -4,6 +4,8 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \ > memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \ > strchr.o strrchr.o > > +lib-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o > + > # Tell the compiler to treat all general purpose registers (with the > # exception of the IP registers, which are already handled by the caller > # in case of a PLT) as callee-saved, which allows for efficient runtime > diff --git a/arch/arm64/lib/ftrace-mod.S b/arch/arm64/lib/ftrace-mod.S > new file mode 100644 > index 000000000000..ce15b9948851 > --- /dev/null > +++ b/arch/arm64/lib/ftrace-mod.S > @@ -0,0 +1,25 @@ > +/* > + * 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" > +ENTRY(__ftrace_trampoline) > + stp x29, x30, [sp, #-16]! > + mov x29, sp > + > + movz x30, #:abs_g3:ftrace_caller > + movk x30, #:abs_g2_nc:ftrace_caller > + movk x30, #:abs_g1_nc:ftrace_caller > + movk x30, #:abs_g0_nc:ftrace_caller > + blr x30 > + > + ldp x29, x30, [sp], #16 > + ret > +ENDPROC(__ftrace_trampoline) I suppose the additional stack frame interferes with correct operation of ftrace() here, so we should probably do this: ENTRY(__ftrace_trampoline) movz x16, #:abs_g3:ftrace_caller movk x16, #:abs_g2_nc:ftrace_caller movk x16, #:abs_g1_nc:ftrace_caller movk x16, #:abs_g0_nc:ftrace_caller blr x16 ENDPROC(__ftrace_trampoline) instead.
On Mon, 10 Apr 2017 15:22:24 +0100 Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 10 April 2017 at 15:13, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > > Currently, dynamic ftrace support in the arm64 kernel assumes that all > > core kernel code is within range of ordinary branch instructions in > > module code, which is usually the case, but is no longer guaranteed now > > that we have support for module PLTs and address space randomization. > > > > Since all patching of branch instructions involves function calls to > > ftrace_caller(), we can emit the modules with a trampoline that has > > unlimited range, and patch the branch instruction to call the trampoline > > if ftrace_caller() itself is out of range. > > > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > > --- > > arch/arm64/Kconfig | 2 +- > > arch/arm64/Makefile | 3 ++ > > arch/arm64/include/asm/module.h | 3 ++ > > arch/arm64/kernel/ftrace.c | 37 ++++++++++++++++++-- > > arch/arm64/kernel/module-plts.c | 10 ++++++ > > arch/arm64/lib/Makefile | 2 ++ > > arch/arm64/lib/ftrace-mod.S | 25 +++++++++++++ > > 7 files changed, 78 insertions(+), 4 deletions(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index e7f043efff41..31af7ea72072 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -982,7 +982,7 @@ config RANDOMIZE_BASE > > > > config RANDOMIZE_MODULE_REGION_FULL > > bool "Randomize the module region independently from the core kernel" > > - depends on RANDOMIZE_BASE && !DYNAMIC_FTRACE > > + depends on RANDOMIZE_BASE > > default y > > help > > Randomizes the location of the module region without considering the > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > > index b9a4a934ca05..01498eab5ada 100644 > > --- a/arch/arm64/Makefile > > +++ b/arch/arm64/Makefile > > @@ -68,6 +68,9 @@ 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/lib/ftrace-mod.o > > +endif > > endif > > > > # Default value > > diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h > > index e12af6754634..2ff2b7782957 100644 > > --- a/arch/arm64/include/asm/module.h > > +++ b/arch/arm64/include/asm/module.h > > @@ -25,6 +25,9 @@ struct mod_arch_specific { > > struct elf64_shdr *plt; > > int plt_num_entries; > > int plt_max_entries; > > + > > + /* for CONFIG_DYNAMIC_FTRACE */ > > + struct elf64_shdr *ftrace_trampoline; > > }; > > #endif > > > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > > index a8db6857cad6..8f5a7dc36c1b 100644 > > --- a/arch/arm64/kernel/ftrace.c > > +++ b/arch/arm64/kernel/ftrace.c > > @@ -9,11 +9,14 @@ > > * published by the Free Software Foundation. > > */ > > > > +#include <linux/elf.h> > > #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> > > > > @@ -63,6 +66,35 @@ int ftrace_update_ftrace_func(ftrace_func_t func) > > return ftrace_modify_code(pc, 0, new, false); > > } > > > > +#ifdef CONFIG_ARM64_MODULE_PLTS > > +EXPORT_SYMBOL_GPL(ftrace_caller); > > +#endif > > + > > +static u32 __ftrace_gen_branch(unsigned long pc, unsigned long addr) > > +{ > > + long offset = (long)pc - (long)addr; > > + struct module *mod; > > + > > + if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && > > + addr == (unsigned long)&ftrace_caller && > > + unlikely(offset < -SZ_128M || offset >= SZ_128M)) { > > + > > + /* > > + * On kernels that support module PLTs, the offset between the > > + * call and its target may legally exceed the range of an > > + * ordinary branch instruction. In this case, we need to branch > > + * via a trampoline in the module. > > + */ > > + mod = __module_address(pc); > > + if (WARN_ON(!mod)) > > + return AARCH64_BREAK_FAULT; > > + > > + addr = (unsigned long)mod->arch.ftrace_trampoline->sh_addr; > > + } > > + > > + return aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); > > +} > > + > > /* > > * Turn on the call to ftrace_caller() in instrumented function > > */ > > @@ -72,7 +104,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) > > u32 old, new; > > > > old = aarch64_insn_gen_nop(); > > - new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); > > + new = __ftrace_gen_branch(pc, addr); > > > > return ftrace_modify_code(pc, old, new, true); > > } > > @@ -87,8 +119,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, > > u32 old = 0, new; > > > > if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) > > - old = aarch64_insn_gen_branch_imm(pc, addr, > > - AARCH64_INSN_BRANCH_LINK); > > + old = __ftrace_gen_branch(pc, addr); > > new = aarch64_insn_gen_nop(); > > > > return ftrace_modify_code(pc, old, new, > > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > > index 1ce90d8450ae..859c7170e69a 100644 > > --- a/arch/arm64/kernel/module-plts.c > > +++ b/arch/arm64/kernel/module-plts.c > > @@ -162,6 +162,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > > mod->arch.plt = sechdrs + i; > > else if (sechdrs[i].sh_type == SHT_SYMTAB) > > syms = (Elf64_Sym *)sechdrs[i].sh_addr; > > + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && > > + strcmp(".text.ftrace_trampoline", > > + secstrings + sechdrs[i].sh_name) == 0) > > + mod->arch.ftrace_trampoline = sechdrs + i; > > } > > > > if (!mod->arch.plt) { > > @@ -173,6 +177,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > > return -ENOEXEC; > > } > > > > + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && !mod->arch.ftrace_trampoline) { > > + pr_err("%s: module ftrace trampoline section missing\n", > > + mod->name); > > + return -ENOEXEC; > > + } > > + > > for (i = 0; i < ehdr->e_shnum; i++) { > > Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; > > int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); > > diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile > > index c86b7909ef31..b01dcfa9c002 100644 > > --- a/arch/arm64/lib/Makefile > > +++ b/arch/arm64/lib/Makefile > > @@ -4,6 +4,8 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \ > > memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \ > > strchr.o strrchr.o > > > > +lib-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o > > + > > # Tell the compiler to treat all general purpose registers (with the > > # exception of the IP registers, which are already handled by the caller > > # in case of a PLT) as callee-saved, which allows for efficient runtime > > diff --git a/arch/arm64/lib/ftrace-mod.S b/arch/arm64/lib/ftrace-mod.S > > new file mode 100644 > > index 000000000000..ce15b9948851 > > --- /dev/null > > +++ b/arch/arm64/lib/ftrace-mod.S > > @@ -0,0 +1,25 @@ > > +/* > > + * 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" > > +ENTRY(__ftrace_trampoline) > > + stp x29, x30, [sp, #-16]! > > + mov x29, sp > > + > > + movz x30, #:abs_g3:ftrace_caller > > + movk x30, #:abs_g2_nc:ftrace_caller > > + movk x30, #:abs_g1_nc:ftrace_caller > > + movk x30, #:abs_g0_nc:ftrace_caller > > + blr x30 > > + > > + ldp x29, x30, [sp], #16 > > + ret > > +ENDPROC(__ftrace_trampoline) > > I suppose the additional stack frame interferes with correct operation > of ftrace() here, so we should probably do this: > > ENTRY(__ftrace_trampoline) > movz x16, #:abs_g3:ftrace_caller > movk x16, #:abs_g2_nc:ftrace_caller > movk x16, #:abs_g1_nc:ftrace_caller > movk x16, #:abs_g0_nc:ftrace_caller > blr x16 Then should that still be a blr or just a br? -- Steve > ENDPROC(__ftrace_trampoline) > > instead.
On 10 April 2017 at 15:39, Steven Rostedt <rostedt@goodmis.org> wrote: > On Mon, 10 Apr 2017 15:22:24 +0100 > Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > >> On 10 April 2017 at 15:13, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: >> > Currently, dynamic ftrace support in the arm64 kernel assumes that all >> > core kernel code is within range of ordinary branch instructions in >> > module code, which is usually the case, but is no longer guaranteed now >> > that we have support for module PLTs and address space randomization. >> > >> > Since all patching of branch instructions involves function calls to >> > ftrace_caller(), we can emit the modules with a trampoline that has >> > unlimited range, and patch the branch instruction to call the trampoline >> > if ftrace_caller() itself is out of range. >> > >> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> >> > --- >> > arch/arm64/Kconfig | 2 +- >> > arch/arm64/Makefile | 3 ++ >> > arch/arm64/include/asm/module.h | 3 ++ >> > arch/arm64/kernel/ftrace.c | 37 ++++++++++++++++++-- >> > arch/arm64/kernel/module-plts.c | 10 ++++++ >> > arch/arm64/lib/Makefile | 2 ++ >> > arch/arm64/lib/ftrace-mod.S | 25 +++++++++++++ >> > 7 files changed, 78 insertions(+), 4 deletions(-) >> > >> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> > index e7f043efff41..31af7ea72072 100644 >> > --- a/arch/arm64/Kconfig >> > +++ b/arch/arm64/Kconfig >> > @@ -982,7 +982,7 @@ config RANDOMIZE_BASE >> > >> > config RANDOMIZE_MODULE_REGION_FULL >> > bool "Randomize the module region independently from the core kernel" >> > - depends on RANDOMIZE_BASE && !DYNAMIC_FTRACE >> > + depends on RANDOMIZE_BASE >> > default y >> > help >> > Randomizes the location of the module region without considering the >> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile >> > index b9a4a934ca05..01498eab5ada 100644 >> > --- a/arch/arm64/Makefile >> > +++ b/arch/arm64/Makefile >> > @@ -68,6 +68,9 @@ 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/lib/ftrace-mod.o >> > +endif >> > endif >> > >> > # Default value >> > diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h >> > index e12af6754634..2ff2b7782957 100644 >> > --- a/arch/arm64/include/asm/module.h >> > +++ b/arch/arm64/include/asm/module.h >> > @@ -25,6 +25,9 @@ struct mod_arch_specific { >> > struct elf64_shdr *plt; >> > int plt_num_entries; >> > int plt_max_entries; >> > + >> > + /* for CONFIG_DYNAMIC_FTRACE */ >> > + struct elf64_shdr *ftrace_trampoline; >> > }; >> > #endif >> > >> > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c >> > index a8db6857cad6..8f5a7dc36c1b 100644 >> > --- a/arch/arm64/kernel/ftrace.c >> > +++ b/arch/arm64/kernel/ftrace.c >> > @@ -9,11 +9,14 @@ >> > * published by the Free Software Foundation. >> > */ >> > >> > +#include <linux/elf.h> >> > #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> >> > >> > @@ -63,6 +66,35 @@ int ftrace_update_ftrace_func(ftrace_func_t func) >> > return ftrace_modify_code(pc, 0, new, false); >> > } >> > >> > +#ifdef CONFIG_ARM64_MODULE_PLTS >> > +EXPORT_SYMBOL_GPL(ftrace_caller); >> > +#endif >> > + >> > +static u32 __ftrace_gen_branch(unsigned long pc, unsigned long addr) >> > +{ >> > + long offset = (long)pc - (long)addr; >> > + struct module *mod; >> > + >> > + if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && >> > + addr == (unsigned long)&ftrace_caller && >> > + unlikely(offset < -SZ_128M || offset >= SZ_128M)) { >> > + >> > + /* >> > + * On kernels that support module PLTs, the offset between the >> > + * call and its target may legally exceed the range of an >> > + * ordinary branch instruction. In this case, we need to branch >> > + * via a trampoline in the module. >> > + */ >> > + mod = __module_address(pc); >> > + if (WARN_ON(!mod)) >> > + return AARCH64_BREAK_FAULT; >> > + >> > + addr = (unsigned long)mod->arch.ftrace_trampoline->sh_addr; >> > + } >> > + >> > + return aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); >> > +} >> > + >> > /* >> > * Turn on the call to ftrace_caller() in instrumented function >> > */ >> > @@ -72,7 +104,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) >> > u32 old, new; >> > >> > old = aarch64_insn_gen_nop(); >> > - new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); >> > + new = __ftrace_gen_branch(pc, addr); >> > >> > return ftrace_modify_code(pc, old, new, true); >> > } >> > @@ -87,8 +119,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, >> > u32 old = 0, new; >> > >> > if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) >> > - old = aarch64_insn_gen_branch_imm(pc, addr, >> > - AARCH64_INSN_BRANCH_LINK); >> > + old = __ftrace_gen_branch(pc, addr); >> > new = aarch64_insn_gen_nop(); >> > >> > return ftrace_modify_code(pc, old, new, >> > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c >> > index 1ce90d8450ae..859c7170e69a 100644 >> > --- a/arch/arm64/kernel/module-plts.c >> > +++ b/arch/arm64/kernel/module-plts.c >> > @@ -162,6 +162,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, >> > mod->arch.plt = sechdrs + i; >> > else if (sechdrs[i].sh_type == SHT_SYMTAB) >> > syms = (Elf64_Sym *)sechdrs[i].sh_addr; >> > + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && >> > + strcmp(".text.ftrace_trampoline", >> > + secstrings + sechdrs[i].sh_name) == 0) >> > + mod->arch.ftrace_trampoline = sechdrs + i; >> > } >> > >> > if (!mod->arch.plt) { >> > @@ -173,6 +177,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, >> > return -ENOEXEC; >> > } >> > >> > + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && !mod->arch.ftrace_trampoline) { >> > + pr_err("%s: module ftrace trampoline section missing\n", >> > + mod->name); >> > + return -ENOEXEC; >> > + } >> > + >> > for (i = 0; i < ehdr->e_shnum; i++) { >> > Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; >> > int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); >> > diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile >> > index c86b7909ef31..b01dcfa9c002 100644 >> > --- a/arch/arm64/lib/Makefile >> > +++ b/arch/arm64/lib/Makefile >> > @@ -4,6 +4,8 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \ >> > memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \ >> > strchr.o strrchr.o >> > >> > +lib-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o >> > + >> > # Tell the compiler to treat all general purpose registers (with the >> > # exception of the IP registers, which are already handled by the caller >> > # in case of a PLT) as callee-saved, which allows for efficient runtime >> > diff --git a/arch/arm64/lib/ftrace-mod.S b/arch/arm64/lib/ftrace-mod.S >> > new file mode 100644 >> > index 000000000000..ce15b9948851 >> > --- /dev/null >> > +++ b/arch/arm64/lib/ftrace-mod.S >> > @@ -0,0 +1,25 @@ >> > +/* >> > + * 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" >> > +ENTRY(__ftrace_trampoline) >> > + stp x29, x30, [sp, #-16]! >> > + mov x29, sp >> > + >> > + movz x30, #:abs_g3:ftrace_caller >> > + movk x30, #:abs_g2_nc:ftrace_caller >> > + movk x30, #:abs_g1_nc:ftrace_caller >> > + movk x30, #:abs_g0_nc:ftrace_caller >> > + blr x30 >> > + >> > + ldp x29, x30, [sp], #16 >> > + ret >> > +ENDPROC(__ftrace_trampoline) >> >> I suppose the additional stack frame interferes with correct operation >> of ftrace() here, so we should probably do this: >> >> ENTRY(__ftrace_trampoline) >> movz x16, #:abs_g3:ftrace_caller >> movk x16, #:abs_g2_nc:ftrace_caller >> movk x16, #:abs_g1_nc:ftrace_caller >> movk x16, #:abs_g0_nc:ftrace_caller >> blr x16 > > Then should that still be a blr or just a br? > Yes, you're quite right. br not blr
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index e7f043efff41..31af7ea72072 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -982,7 +982,7 @@ config RANDOMIZE_BASE config RANDOMIZE_MODULE_REGION_FULL bool "Randomize the module region independently from the core kernel" - depends on RANDOMIZE_BASE && !DYNAMIC_FTRACE + depends on RANDOMIZE_BASE default y help Randomizes the location of the module region without considering the diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index b9a4a934ca05..01498eab5ada 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -68,6 +68,9 @@ 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/lib/ftrace-mod.o +endif endif # Default value diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/module.h index e12af6754634..2ff2b7782957 100644 --- a/arch/arm64/include/asm/module.h +++ b/arch/arm64/include/asm/module.h @@ -25,6 +25,9 @@ struct mod_arch_specific { struct elf64_shdr *plt; int plt_num_entries; int plt_max_entries; + + /* for CONFIG_DYNAMIC_FTRACE */ + struct elf64_shdr *ftrace_trampoline; }; #endif diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index a8db6857cad6..8f5a7dc36c1b 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -9,11 +9,14 @@ * published by the Free Software Foundation. */ +#include <linux/elf.h> #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> @@ -63,6 +66,35 @@ int ftrace_update_ftrace_func(ftrace_func_t func) return ftrace_modify_code(pc, 0, new, false); } +#ifdef CONFIG_ARM64_MODULE_PLTS +EXPORT_SYMBOL_GPL(ftrace_caller); +#endif + +static u32 __ftrace_gen_branch(unsigned long pc, unsigned long addr) +{ + long offset = (long)pc - (long)addr; + struct module *mod; + + if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && + addr == (unsigned long)&ftrace_caller && + unlikely(offset < -SZ_128M || offset >= SZ_128M)) { + + /* + * On kernels that support module PLTs, the offset between the + * call and its target may legally exceed the range of an + * ordinary branch instruction. In this case, we need to branch + * via a trampoline in the module. + */ + mod = __module_address(pc); + if (WARN_ON(!mod)) + return AARCH64_BREAK_FAULT; + + addr = (unsigned long)mod->arch.ftrace_trampoline->sh_addr; + } + + return aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); +} + /* * Turn on the call to ftrace_caller() in instrumented function */ @@ -72,7 +104,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) u32 old, new; old = aarch64_insn_gen_nop(); - new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); + new = __ftrace_gen_branch(pc, addr); return ftrace_modify_code(pc, old, new, true); } @@ -87,8 +119,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, u32 old = 0, new; if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) - old = aarch64_insn_gen_branch_imm(pc, addr, - AARCH64_INSN_BRANCH_LINK); + old = __ftrace_gen_branch(pc, addr); new = aarch64_insn_gen_nop(); return ftrace_modify_code(pc, old, new, diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c index 1ce90d8450ae..859c7170e69a 100644 --- a/arch/arm64/kernel/module-plts.c +++ b/arch/arm64/kernel/module-plts.c @@ -162,6 +162,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, mod->arch.plt = sechdrs + i; else if (sechdrs[i].sh_type == SHT_SYMTAB) syms = (Elf64_Sym *)sechdrs[i].sh_addr; + else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && + strcmp(".text.ftrace_trampoline", + secstrings + sechdrs[i].sh_name) == 0) + mod->arch.ftrace_trampoline = sechdrs + i; } if (!mod->arch.plt) { @@ -173,6 +177,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, return -ENOEXEC; } + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && !mod->arch.ftrace_trampoline) { + pr_err("%s: module ftrace trampoline section missing\n", + mod->name); + return -ENOEXEC; + } + for (i = 0; i < ehdr->e_shnum; i++) { Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile index c86b7909ef31..b01dcfa9c002 100644 --- a/arch/arm64/lib/Makefile +++ b/arch/arm64/lib/Makefile @@ -4,6 +4,8 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \ memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \ strchr.o strrchr.o +lib-$(CONFIG_DYNAMIC_FTRACE) += ftrace-mod.o + # Tell the compiler to treat all general purpose registers (with the # exception of the IP registers, which are already handled by the caller # in case of a PLT) as callee-saved, which allows for efficient runtime diff --git a/arch/arm64/lib/ftrace-mod.S b/arch/arm64/lib/ftrace-mod.S new file mode 100644 index 000000000000..ce15b9948851 --- /dev/null +++ b/arch/arm64/lib/ftrace-mod.S @@ -0,0 +1,25 @@ +/* + * 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" +ENTRY(__ftrace_trampoline) + stp x29, x30, [sp, #-16]! + mov x29, sp + + movz x30, #:abs_g3:ftrace_caller + movk x30, #:abs_g2_nc:ftrace_caller + movk x30, #:abs_g1_nc:ftrace_caller + movk x30, #:abs_g0_nc:ftrace_caller + blr x30 + + ldp x29, x30, [sp], #16 + ret +ENDPROC(__ftrace_trampoline)
Currently, dynamic ftrace support in the arm64 kernel assumes that all core kernel code is within range of ordinary branch instructions in module code, which is usually the case, but is no longer guaranteed now that we have support for module PLTs and address space randomization. Since all patching of branch instructions involves function calls to ftrace_caller(), we can emit the modules with a trampoline that has unlimited range, and patch the branch instruction to call the trampoline if ftrace_caller() itself is out of range. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm64/Kconfig | 2 +- arch/arm64/Makefile | 3 ++ arch/arm64/include/asm/module.h | 3 ++ arch/arm64/kernel/ftrace.c | 37 ++++++++++++++++++-- arch/arm64/kernel/module-plts.c | 10 ++++++ arch/arm64/lib/Makefile | 2 ++ arch/arm64/lib/ftrace-mod.S | 25 +++++++++++++ 7 files changed, 78 insertions(+), 4 deletions(-)