Re: [PATCH v7 8/9] LoongArch: modules/ftrace: Initialize PLT at load time

From: Huacai Chen
Date: Wed Nov 16 2022 - 01:38:21 EST

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Hi, Qing,

On Wed, Nov 16, 2022 at 10:53 AM Qing Zhang <zhangqing@xxxxxxxxxxx> wrote:
>
> To Implement ftrace trampiones through plt entry.
>
> Tested by forcing ftrace_make_call() to use the module PLT, and then
> loading up a module after setting up ftrace with:
>
> | echo ":mod:<module-name>" > set_ftrace_filter;
> | echo function > current_tracer;
> | modprobe <module-name>
>
> Since FTRACE_ADDR/FTRACE_REGS_ADDR is only defined when CONFIG_DYNAMIC_FTRACE
> is selected, we wrap its use along with most of module_init_ftrace_plt() with
> ifdeffery rather than using IS_ENABLED().
>
> Signed-off-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
> ---
> arch/loongarch/include/asm/ftrace.h | 4 ++
> arch/loongarch/include/asm/inst.h | 3 +
> arch/loongarch/include/asm/module.h | 5 +-
> arch/loongarch/include/asm/module.lds.h | 1 +
> arch/loongarch/kernel/ftrace_dyn.c | 79 +++++++++++++++++++++++++
> arch/loongarch/kernel/inst.c | 11 ++++
> arch/loongarch/kernel/module-sections.c | 11 ++++
> arch/loongarch/kernel/module.c | 22 +++++++
> 8 files changed, 135 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
> index 1583ec2171fc..8d194f6da8af 100644
> --- a/arch/loongarch/include/asm/ftrace.h
> +++ b/arch/loongarch/include/asm/ftrace.h
> @@ -8,6 +8,10 @@
>
> #define GRAPH_FAKE_OFFSET (sizeof(struct pt_regs) - offsetof(struct pt_regs, regs[1]))
>
> +#define FTRACE_PLT_IDX 0
> +#define FTRACE_REGS_PLT_IDX 1
> +#define NR_FTRACE_PLTS 2
> +
> #ifdef CONFIG_FUNCTION_TRACER
> #define MCOUNT_INSN_SIZE 4 /* sizeof mcount call */
>
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index 59fee75590e9..417d6b8bc43e 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -13,10 +13,12 @@
>
> #define ADDR_IMMMASK_LU52ID 0xFFF0000000000000
> #define ADDR_IMMMASK_LU32ID 0x000FFFFF00000000
> +#define ADDR_IMMMASK_LU12IW 0x00000000FFFFF000
> #define ADDR_IMMMASK_ADDU16ID 0x00000000FFFF0000
>
> #define ADDR_IMMSHIFT_LU52ID 52
> #define ADDR_IMMSHIFT_LU32ID 32
> +#define ADDR_IMMSHIFT_LU12IW 12
> #define ADDR_IMMSHIFT_ADDU16ID 16
>
> #define ADDR_IMM(addr, INSN) ((addr & ADDR_IMMMASK_##INSN) >> ADDR_IMMSHIFT_##INSN)
> @@ -361,6 +363,7 @@ u32 larch_insn_gen_or(enum loongarch_gpr rd, enum loongarch_gpr rj,
> enum loongarch_gpr rk);
> u32 larch_insn_gen_move(enum loongarch_gpr rd, enum loongarch_gpr rj);
>
> +u32 larch_insn_gen_lu12iw(enum loongarch_gpr rd, int imm);
> u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
> u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
> u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);
> diff --git a/arch/loongarch/include/asm/module.h b/arch/loongarch/include/asm/module.h
> index b29b19a46f42..a311cfec2b23 100644
> --- a/arch/loongarch/include/asm/module.h
> +++ b/arch/loongarch/include/asm/module.h
> @@ -20,6 +20,9 @@ struct mod_arch_specific {
> struct mod_section got;
> struct mod_section plt;
> struct mod_section plt_idx;
> +
> + /* for CONFIG_DYNAMIC_FTRACE */
> + struct plt_entry *ftrace_trampolines;
> };
>
> struct got_entry {
> @@ -49,7 +52,7 @@ static inline struct plt_entry emit_plt_entry(unsigned long val)
> {
> u32 lu12iw, lu32id, lu52id, jirl;
>
> - lu12iw = (lu12iw_op << 25 | (((val >> 12) & 0xfffff) << 5) | LOONGARCH_GPR_T1);
> + lu12iw = larch_insn_gen_lu12iw(LOONGARCH_GPR_T1, ADDR_IMM(val, LU12IW));
> lu32id = larch_insn_gen_lu32id(LOONGARCH_GPR_T1, ADDR_IMM(val, LU32ID));
> lu52id = larch_insn_gen_lu52id(LOONGARCH_GPR_T1, LOONGARCH_GPR_T1, ADDR_IMM(val, LU52ID));
> jirl = larch_insn_gen_jirl(0, LOONGARCH_GPR_T1, 0, (val & 0xfff));
> diff --git a/arch/loongarch/include/asm/module.lds.h b/arch/loongarch/include/asm/module.lds.h
> index a3d1bc0fcc72..438f09d4ccf4 100644
> --- a/arch/loongarch/include/asm/module.lds.h
> +++ b/arch/loongarch/include/asm/module.lds.h
> @@ -5,4 +5,5 @@ SECTIONS {
> .got : { BYTE(0) }
> .plt : { BYTE(0) }
> .plt.idx : { BYTE(0) }
> + .ftrace_trampoline : { BYTE(0) }
> }
> diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
> index cd64887e26b5..b070ce225989 100644
> --- a/arch/loongarch/kernel/ftrace_dyn.c
> +++ b/arch/loongarch/kernel/ftrace_dyn.c
> @@ -9,6 +9,7 @@
> #include <linux/uaccess.h>
>
> #include <asm/inst.h>
> +#include <asm/module.h>
>
> static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
> bool validate)
> @@ -72,12 +73,63 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
> return ftrace_modify_code(pc, old, new, true);
> }
>
> +static inline int __get_mod(struct module **mod, unsigned long addr)
> +{
> + preempt_disable();
> + *mod = __module_text_address(addr);
> + preempt_enable();
> +
> + if (WARN_ON(!(*mod)))
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> +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_DYNAMIC_FTRACE_WITH_REGS))
> + return &plt[FTRACE_REGS_PLT_IDX];
> +
> + return NULL;
> +}
> +
> +static unsigned long get_plt_addr(struct module *mod, unsigned long addr)
> +{
> + struct plt_entry *plt;
> +
> + plt = get_ftrace_plt(mod, addr);
> + if (!plt) {
> + pr_err("ftrace: no module PLT for %ps\n", (void *)addr);
> + return -EINVAL;
> + }
> +
> + return (unsigned long)plt;
> +}
> +
> int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> {
> unsigned long pc;
> + long offset;
> u32 old, new;
>
> pc = rec->ip + LOONGARCH_INSN_SIZE;
> + offset = (long)pc - (long)addr;
> +
> + if (offset < -SZ_128M || offset >= SZ_128M) {
> + int ret;
> + struct module *mod;
> +
> + ret = __get_mod(&mod, pc);
> + if (ret)
> + return ret;
> +
> + addr = get_plt_addr(mod, addr);
> + }
>
> old = larch_insn_gen_nop();
> new = larch_insn_gen_bl(pc, addr);
> @@ -89,9 +141,22 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
> unsigned long addr)
> {
> unsigned long pc;
> + long offset;
> u32 old, new;
>
> pc = rec->ip + LOONGARCH_INSN_SIZE;
> + offset = (long)pc - (long)addr;
> +
> + if (offset < -SZ_128M || offset >= SZ_128M) {
> + int ret;
> + struct module *mod;
> +
> + ret = __get_mod(&mod, pc);
> + if (ret)
> + return ret;
> +
> + addr = get_plt_addr(mod, addr);
> + }
>
> new = larch_insn_gen_nop();
> old = larch_insn_gen_bl(pc, addr);
> @@ -108,6 +173,20 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
> u32 old, new;
>
> pc = rec->ip + LOONGARCH_INSN_SIZE;
> + offset = (long)pc - (long)addr;
> +
> + if (offset < -SZ_128M || offset >= SZ_128M) {
> + int ret;
> + struct module *mod;
> +
> + ret = __get_mod(&mod, pc);
> + if (ret)
> + return ret;
> +
> + addr = get_plt_addr(mod, addr);
> +
> + old_addr = get_plt_addr(mod, old_addr);
> + }
>
> old = larch_insn_gen_bl(pc, old_addr);
> new = larch_insn_gen_bl(pc, addr);
> diff --git a/arch/loongarch/kernel/inst.c b/arch/loongarch/kernel/inst.c
> index 2d2e942eb06a..0d6bd7000ba6 100644
> --- a/arch/loongarch/kernel/inst.c
> +++ b/arch/loongarch/kernel/inst.c
> @@ -103,6 +103,17 @@ u32 larch_insn_gen_bl(unsigned long pc, unsigned long dest)
> return insn.word;
> }
>
> +u32 larch_insn_gen_lu12iw(enum loongarch_gpr rd, int imm)
> +{
> + union loongarch_instruction insn;
> +
> + insn.reg1i20_format.opcode = lu12iw_op;
> + insn.reg1i20_format.rd = rd;
> + insn.reg1i20_format.immediate = imm;
> +
> + return insn.word;
> +}
> +
> u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm)
> {
> union loongarch_instruction insn;
> diff --git a/arch/loongarch/kernel/module-sections.c b/arch/loongarch/kernel/module-sections.c
> index d296a70b758f..bd1a96691c98 100644
> --- a/arch/loongarch/kernel/module-sections.c
> +++ b/arch/loongarch/kernel/module-sections.c
> @@ -4,6 +4,7 @@
> */
>
> #include <linux/elf.h>
> +#include <linux/ftrace.h>
> #include <linux/kernel.h>
> #include <linux/module.h>
>
> @@ -103,6 +104,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> char *secstrings, struct module *mod)
> {
> unsigned int i, num_plts = 0, num_gots = 0;
> + Elf_Shdr *tramp = NULL;
>
> /*
> * Find the empty .plt sections.
> @@ -114,6 +116,8 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> mod->arch.plt.shdr = sechdrs + i;
> else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt.idx"))
> mod->arch.plt_idx.shdr = sechdrs + i;
> + else if (!strcmp(secstrings + sechdrs[i].sh_name, ".ftrace_trampoline"))
> + tramp = sechdrs + i;
> }
>
> if (!mod->arch.got.shdr) {
> @@ -166,5 +170,12 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> mod->arch.plt_idx.num_entries = 0;
> mod->arch.plt_idx.max_entries = num_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 = NR_FTRACE_PLTS * sizeof(struct plt_entry);
> + }
> +
> return 0;
> }
> diff --git a/arch/loongarch/kernel/module.c b/arch/loongarch/kernel/module.c
> index 825fcf77f9e7..a606a0cab968 100644
> --- a/arch/loongarch/kernel/module.c
> +++ b/arch/loongarch/kernel/module.c
> @@ -10,6 +10,7 @@
>
> #include <linux/moduleloader.h>
> #include <linux/elf.h>
> +#include <linux/ftrace.h>
> #include <linux/mm.h>
> #include <linux/numa.h>
> #include <linux/vmalloc.h>
> @@ -18,6 +19,7 @@
> #include <linux/string.h>
> #include <linux/kernel.h>
> #include <asm/alternative.h>
> +#include <asm/inst.h>
>
> static int rela_stack_push(s64 stack_value, s64 *rela_stack, size_t *rela_stack_top)
> {
> @@ -458,6 +460,24 @@ void *module_alloc(unsigned long size)
> GFP_KERNEL, PAGE_KERNEL, 0, NUMA_NO_NODE, __builtin_return_address(0));
> }
>
> +static int module_init_ftrace_plt(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
> + struct module *mod)
> +{
> +#ifdef CONFIG_DYNAMIC_FTRACE
> + struct plt_entry *ftrace_plts;
> +
> + ftrace_plts = (void *)sechdrs->sh_addr;
> +
> + ftrace_plts[FTRACE_PLT_IDX] = emit_plt_entry(FTRACE_ADDR);
> +
> + if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
> + ftrace_plts[FTRACE_REGS_PLT_IDX] = emit_plt_entry(FTRACE_REGS_ADDR);
> +
> + mod->arch.ftrace_trampolines = ftrace_plts;
> +#endif
> + return 0;
> +}
> +
> int module_finalize(const Elf_Ehdr *hdr,
> const Elf_Shdr *sechdrs, struct module *mod)
> {
> @@ -467,6 +487,8 @@ int module_finalize(const Elf_Ehdr *hdr,
> for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++) {
> if (!strcmp(".altinstructions", secstrs + s->sh_name))
> apply_alternatives((void *)s->sh_addr, (void *)s->sh_addr + s->sh_size);
> + if (!strcmp(".ftrace_trampoline", secstrs + s->sh_name))
> + return module_init_ftrace_plt(hdr, s, mod);
We shouldn't return here, because we are in a loop, if
.ftrace_trampoline is before .altinstructions, we will lose the
apply_alternatives() call.

Huacai
> }
>
> return 0;
> --
> 2.36.0
>

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