On Fri, Nov 15, 2019 at 07:05:39AM +0900, Itaru Kitayama wrote: > Is this feature avail even when building kernel with Clang? Clang doesn't currently support -fpatchable-function-entry. Nick (Cc'd) created an LLVM bugzilla ticket for that: https://bugs.llvm.org/show_bug.cgi?id=43912 ... though it looks like that's having database issues at the moment. Thanks, Mark. > On Wed, Oct 30, 2019 at 2:01 Mark Rutland <mark.rutland@xxxxxxx> wrote: > > From: Torsten Duwe <duwe@xxxxxx> > > This patch implements FTRACE_WITH_REGS for arm64, which allows a traced > function's arguments (and some other registers) to be captured into a > struct pt_regs, allowing these to be inspected and/or modified. This is > a building block for live-patching, where a function's arguments may be > forwarded to another function. This is also necessary to enable ftrace > and in-kernel pointer authentication at the same time, as it allows the > LR value to be captured and adjusted prior to signing. > > Using GCC's -fpatchable-function-entry=N option, we can have the > compiler insert a configurable number of NOPs between the function entry > point and the usual prologue. This also ensures functions are AAPCS > compliant (e.g. disabling inter-procedural register allocation). > > For example, with -fpatchable-function-entry=2, GCC 8.1.0 compiles the > following: > > | unsigned long bar(void); > | > | unsigned long foo(void) > | { > | return bar() + 1; > | } > > ... to: > > | <foo>: > | nop > | nop > | stp x29, x30, [sp, #-16]! > | mov x29, sp > | bl 0 <bar> > | add x0, x0, #0x1 > | ldp x29, x30, [sp], #16 > | ret > > This patch builds the kernel with -fpatchable-function-entry=2, > prefixing each function with two NOPs. To trace a function, we replace > these NOPs with a sequence that saves the LR into a GPR, then calls an > ftrace entry assembly function which saves this and other relevant > registers: > > | mov x9, x30 > | bl <ftrace-entry> > > Since patchable functions are AAPCS compliant (and the kernel does not > use x18 as a platform register), x9-x18 can be safely clobbered in the > patched sequence and the ftrace entry code. > > There are now two ftrace entry functions, ftrace_regs_entry (which saves > all GPRs), and ftrace_entry (which saves the bare minimum). A PLT is > allocated for each within modules. > > Signed-off-by: Torsten Duwe <duwe@xxxxxxx> > [Mark: rework asm, comments, PLTs, initialization, commit message] > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> > Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Cc: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> > Cc: Amit Daniel Kachhap <amit.kachhap@xxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > Cc: Julien Thierry <jthierry@xxxxxxxxxx> > Cc: Will Deacon <will@xxxxxxxxxx> > --- > arch/arm64/Kconfig | 2 + > arch/arm64/Makefile | 5 ++ > arch/arm64/include/asm/ftrace.h | 23 +++++++ > arch/arm64/include/asm/module.h | 2 +- > arch/arm64/kernel/entry-ftrace.S | 140 > +++++++++++++++++++++++++++++++++++++-- > arch/arm64/kernel/ftrace.c | 84 +++++++++++++++++++---- > arch/arm64/kernel/module-plts.c | 3 +- > arch/arm64/kernel/module.c | 18 +++-- > 8 files changed, 252 insertions(+), 25 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 950a56b71ff0..0ffb8596b8a1 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -143,6 +143,8 @@ config ARM64 > select HAVE_DEBUG_KMEMLEAK > select HAVE_DMA_CONTIGUOUS > select HAVE_DYNAMIC_FTRACE > + select HAVE_DYNAMIC_FTRACE_WITH_REGS \ > + if $(cc-option,-fpatchable-function-entry=2) > select HAVE_EFFICIENT_UNALIGNED_ACCESS > select HAVE_FAST_GUP > select HAVE_FTRACE_MCOUNT_RECORD > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 2c0238ce0551..1fbe24d4fdb6 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -95,6 +95,11 @@ ifeq ($(CONFIG_ARM64_MODULE_PLTS),y) > KBUILD_LDS_MODULE += $(srctree)/arch/arm64/kernel/module.lds > endif > > +ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y) > + KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY > + CC_FLAGS_FTRACE := -fpatchable-function-entry=2 > +endif > + > # Default value > head-y := arch/arm64/kernel/head.o > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ > ftrace.h > index d48667b04c41..91fa4baa1a93 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -11,9 +11,20 @@ > #include <asm/insn.h> > > #define HAVE_FUNCTION_GRAPH_FP_TEST > + > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > +#define ARCH_SUPPORTS_FTRACE_OPS 1 > +#else > #define MCOUNT_ADDR ((unsigned long)_mcount) > +#endif > + > +/* The BL at the callsite's adjusted rec->ip */ > #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE > > +#define FTRACE_PLT_IDX 0 > +#define FTRACE_REGS_PLT_IDX 1 > +#define NR_FTRACE_PLTS 2 > + > /* > * Currently, gcc tends to save the link register after the local > variables > * on the stack. This causes the max stack tracer to report the function > @@ -44,12 +55,24 @@ extern void return_to_handler(void); > static inline unsigned long ftrace_call_adjust(unsigned long addr) > { > /* > + * Adjust addr to point at the BL in the callsite. > + * See ftrace_init_nop() for the callsite sequence. > + */ > + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS)) > + return addr + AARCH64_INSN_SIZE; > + /* > * addr is the address of the mcount call instruction. > * recordmcount does the necessary offset calculation. > */ > return addr; > } > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > +struct dyn_ftrace; > +int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec); > +#define ftrace_init_nop ftrace_init_nop > +#endif > + > #define ftrace_return_address(n) return_address(n) > > /* > diff --git a/arch/arm64/include/asm/module.h b/arch/arm64/include/asm/ > module.h > index f80e13cbf8ec..1e93de68c044 100644 > --- a/arch/arm64/include/asm/module.h > +++ b/arch/arm64/include/asm/module.h > @@ -21,7 +21,7 @@ struct mod_arch_specific { > struct mod_plt_sec init; > > /* for CONFIG_DYNAMIC_FTRACE */ > - struct plt_entry *ftrace_trampoline; > + struct plt_entry *ftrace_trampolines; > }; > #endif > > diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/ > entry-ftrace.S > index 33d003d80121..94720388957f 100644 > --- a/arch/arm64/kernel/entry-ftrace.S > +++ b/arch/arm64/kernel/entry-ftrace.S > @@ -7,10 +7,137 @@ > */ > > #include <linux/linkage.h> > +#include <asm/asm-offsets.h> > #include <asm/assembler.h> > #include <asm/ftrace.h> > #include <asm/insn.h> > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > +/* > + * Due to -fpatchable-function-entry=2, the compiler has placed two NOPs > before > + * the regular function prologue. For an enabled callsite, ftrace_init_nop > () and > + * ftrace_make_call() have patched those NOPs to: > + * > + * MOV X9, LR > + * BL <entry> > + * > + * ... where <entry> is either ftrace_caller or ftrace_regs_caller. > + * > + * Each instrumented function follows the AAPCS, so here x0-x8 and x19-x30 > are > + * live, and x9-x18 are safe to clobber. > + * > + * We save the callsite's context into a pt_regs before invoking and > ftrace > + * callbacks. So that we can get a sensible backtrace, we create a stack > record > + * for the callsite and the ftrace entry assembly. This is not sufficient > for > + * reliable stacktrace: until we create the callsite stack record, its > caller > + * is missing from the LR and existing chain of frame records. > + */ > + .macro ftrace_regs_entry, allregs=0 > + /* Make room for pt_regs, plus a callee frame */ > + sub sp, sp, #(S_FRAME_SIZE + 16) > + > + /* Save function arguments (and x9 for simplicity) */ > + stp x0, x1, [sp, #S_X0] > + stp x2, x3, [sp, #S_X2] > + stp x4, x5, [sp, #S_X4] > + stp x6, x7, [sp, #S_X6] > + stp x8, x9, [sp, #S_X8] > + > + /* Optionally save the callee-saved registers, always save the FP * > / > + .if \allregs == 1 > + stp x10, x11, [sp, #S_X10] > + stp x12, x13, [sp, #S_X12] > + stp x14, x15, [sp, #S_X14] > + stp x16, x17, [sp, #S_X16] > + stp x18, x19, [sp, #S_X18] > + stp x20, x21, [sp, #S_X20] > + stp x22, x23, [sp, #S_X22] > + stp x24, x25, [sp, #S_X24] > + stp x26, x27, [sp, #S_X26] > + stp x28, x29, [sp, #S_X28] > + .else > + str x29, [sp, #S_FP] > + .endif > + > + /* Save the callsite's SP and LR */ > + add x10, sp, #(S_FRAME_SIZE + 16) > + stp x9, x10, [sp, #S_LR] > + > + /* Save the PC after the ftrace callsite */ > + str x30, [sp, #S_PC] > + > + /* Create a frame record for the callsite above pt_regs */ > + stp x29, x9, [sp, #S_FRAME_SIZE] > + add x29, sp, #S_FRAME_SIZE > + > + /* Create our frame record within pt_regs. */ > + stp x29, x30, [sp, #S_STACKFRAME] > + add x29, sp, #S_STACKFRAME > + .endm > + > +ENTRY(ftrace_regs_caller) > + ftrace_regs_entry 1 > + b ftrace_common > +ENDPROC(ftrace_regs_caller) > + > +ENTRY(ftrace_caller) > + ftrace_regs_entry 0 > + b ftrace_common > +ENDPROC(ftrace_caller) > + > +ENTRY(ftrace_common) > + sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn) > + mov x1, x9 // parent_ip (callsite's > LR) > + ldr_l x2, function_trace_op // op > + mov x3, sp // regs > + > +GLOBAL(ftrace_call) > + bl ftrace_stub > + > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > +GLOBAL(ftrace_graph_call) // ftrace_graph_caller(); > + nop // If enabled, this will be > replaced > + // "b ftrace_graph_caller" > +#endif > + > +/* > + * At the callsite x0-x8 and x19-x30 were live. Any C code will have > preserved > + * x19-x29 per the AAPCS, and we created frame records upon entry, so we > need > + * to restore x0-x8, x29, and x30. > + */ > +ftrace_common_return: > + /* Restore function arguments */ > + ldp x0, x1, [sp] > + ldp x2, x3, [sp, #S_X2] > + ldp x4, x5, [sp, #S_X4] > + ldp x6, x7, [sp, #S_X6] > + ldr x8, [sp, #S_X8] > + > + /* Restore the callsite's FP, LR, PC */ > + ldr x29, [sp, #S_FP] > + ldr x30, [sp, #S_LR] > + ldr x9, [sp, #S_PC] > + > + /* Restore the callsite's SP */ > + add sp, sp, #S_FRAME_SIZE + 16 > + > + ret x9 > +ENDPROC(ftrace_common) > + > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > +ENTRY(ftrace_graph_caller) > + ldr x0, [sp, #S_PC] > + sub x0, x0, #AARCH64_INSN_SIZE // ip (callsite's BL insn) > + add x1, sp, #S_LR // parent_ip (callsite's > LR) > + ldr x2, [sp, #S_FRAME_SIZE] // parent fp (callsite's > FP) > + bl prepare_ftrace_return > + b ftrace_common_return > +ENDPROC(ftrace_graph_caller) > +#else > +#endif > + > +#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */ > + > /* > * Gcc with -pg will put the following code in the beginning of each > function: > * mov x0, x30 > @@ -160,11 +287,6 @@ GLOBAL(ftrace_graph_call) // > ftrace_graph_caller(); > > mcount_exit > ENDPROC(ftrace_caller) > -#endif /* CONFIG_DYNAMIC_FTRACE */ > - > -ENTRY(ftrace_stub) > - ret > -ENDPROC(ftrace_stub) > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > /* > @@ -184,7 +306,15 @@ ENTRY(ftrace_graph_caller) > > mcount_exit > ENDPROC(ftrace_graph_caller) > +#endif /* CONFIG_FUNCTION_GRAPH_TRACER */ > +#endif /* CONFIG_DYNAMIC_FTRACE */ > +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */ > + > +ENTRY(ftrace_stub) > + ret > +ENDPROC(ftrace_stub) > > +#ifdef CONFIG_FUNCTION_GRAPH_TRACER > /* > * void return_to_handler(void) > * > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index 822718eafdb4..aea652c33a38 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -62,6 +62,19 @@ int ftrace_update_ftrace_func(ftrace_func_t func) > return ftrace_modify_code(pc, 0, new, false); > } > > +#ifdef CONFIG_ARM64_MODULE_PLTS > +static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long > addr) > +{ > + struct plt_entry *plt = mod->arch.ftrace_trampolines; > + > + if (addr == FTRACE_ADDR) > + return &plt[FTRACE_PLT_IDX]; > + if (addr == FTRACE_REGS_ADDR && IS_ENABLED > (CONFIG_FTRACE_WITH_REGS)) > + return &plt[FTRACE_REGS_PLT_IDX]; > + return NULL; > +} > +#endif > + > /* > * Turn on the call to ftrace_caller() in instrumented function > */ > @@ -74,19 +87,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned > long addr) > if (offset < -SZ_128M || offset >= SZ_128M) { > #ifdef CONFIG_ARM64_MODULE_PLTS > struct module *mod; > - > - /* > - * There is only one ftrace trampoline per module. For now, > - * this is not a problem since on arm64, all dynamic ftrace > - * invocations are routed via ftrace_caller(). This will > need > - * to be revisited if support for multiple ftrace entry > points > - * is added in the future, but for now, the pr_err() below > - * deals with a theoretical issue only. > - */ > - if (addr != FTRACE_ADDR) { > - pr_err("ftrace: far branches to multiple entry > points unsupported inside a single module\n"); > - return -EINVAL; > - } > + struct plt_entry *plt; > > /* > * On kernels that support module PLTs, the offset between > the > @@ -105,7 +106,13 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned > long addr) > if (WARN_ON(!mod)) > return -EINVAL; > > - addr = (unsigned long)mod->arch.ftrace_trampoline; > + plt = get_ftrace_plt(mod, addr); > + if (!plt) { > + pr_err("ftrace: no module PLT for %ps\n", (void *) > addr); > + return -EINVAL; > + } > + > + addr = (unsigned long)plt; > #else /* CONFIG_ARM64_MODULE_PLTS */ > return -EINVAL; > #endif /* CONFIG_ARM64_MODULE_PLTS */ > @@ -117,6 +124,55 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned > long addr) > return ftrace_modify_code(pc, old, new, true); > } > > +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, > + unsigned long addr) > +{ > + unsigned long pc = rec->ip; > + u32 old, new; > + > + old = aarch64_insn_gen_branch_imm(pc, old_addr, > + AARCH64_INSN_BRANCH_LINK); > + new = aarch64_insn_gen_branch_imm(pc, addr, > AARCH64_INSN_BRANCH_LINK); > + > + return ftrace_modify_code(pc, old, new, true); > +} > + > +/* > + * The compiler has inserted two NOPs before the regular function > prologue. > + * All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are > live, > + * and x9-x18 are free for our use. > + * > + * At runtime we want to be able to swing a single NOP <-> BL to enable or > + * disable the ftrace call. The BL requires us to save the original LR > value, > + * so here we insert a <MOV X9, LR> over the first NOP so the instructions > + * before the regular prologue are: > + * > + * | Compiled | Disabled | Enabled | > + * +----------+------------+------------+ > + * | NOP | MOV X9, LR | MOV X9, LR | > + * | NOP | NOP | BL <entry> | > + * > + * The LR value will be recovered by ftrace_regs_entry, and restored into > LR > + * before returning to the regular function prologue. When a function is > not > + * being traced, the MOV is not harmful given x9 is not live per the > AAPCS. > + * > + * Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address > of > + * the BL. > + */ > +int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) > +{ > + unsigned long pc = rec->ip - AARCH64_INSN_SIZE; > + u32 old, new; > + > + old = aarch64_insn_gen_nop(); > + new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9, > + AARCH64_INSN_REG_LR, > + AARCH64_INSN_VARIANT_64BIT); > + return ftrace_modify_code(pc, old, new, true); > +} > +#endif > + > /* > * Turn off the call to ftrace_caller() in instrumented function > */ > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/ > module-plts.c > index b182442b87a3..65b08a74aec6 100644 > --- a/arch/arm64/kernel/module-plts.c > +++ b/arch/arm64/kernel/module-plts.c > @@ -4,6 +4,7 @@ > */ > > #include <linux/elf.h> > +#include <linux/ftrace.h> > #include <linux/kernel.h> > #include <linux/module.h> > #include <linux/sort.h> > @@ -330,7 +331,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr > *sechdrs, > 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); > + tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry); > } > > return 0; > diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c > index 5f5bc3b94da7..00d21a420c60 100644 > --- a/arch/arm64/kernel/module.c > +++ b/arch/arm64/kernel/module.c > @@ -486,21 +486,31 @@ static const Elf_Shdr *find_section(const Elf_Ehdr > *hdr, > return NULL; > } > > +static inline void __init_plt(struct plt_entry *plt, unsigned long addr) > +{ > + *plt = get_plt_entry(addr, plt); > +} > + > int module_init_ftrace_plt(const Elf_Ehdr *hdr, > const Elf_Shdr *sechdrs, > struct module *mod) > { > #if defined(CONFIG_ARM64_MODULE_PLTS) && defined(CONFIG_DYNAMIC_FTRACE) > const Elf_Shdr *s; > - struct plt_entry *plt; > + struct plt_entry *plts; > > s = find_section(hdr, sechdrs, ".text.ftrace_trampoline"); > if (!s) > return -ENOEXEC; > > - plt = (void *)s->sh_addr; > - *plt = get_plt_entry(FTRACE_ADDR, plt); > - mod->arch.ftrace_trampoline = plt; > + plts = (void *)s->sh_addr; > + > + __init_plt(&plts[FTRACE_PLT_IDX], FTRACE_ADDR); > + > + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS)) > + __init_plt(&plts[FTRACE_REGS_PLT_IDX], FTRACE_REGS_ADDR); > + > + mod->arch.ftrace_trampolines = plts; > #endif > return 0; > } > -- > 2.11.0 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
