[PATCH v2 7/9] LoongArch: modules/ftrace: Initialize PLT at load time

From: Qing Zhang
Date: Fri Aug 26 2022 - 03:36:50 EST

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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 | 47 +++++++++++++++
8 files changed, 160 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
index 4a9db84f8264..ce119496c6d0 100644
--- a/arch/loongarch/include/asm/ftrace.h
+++ b/arch/loongarch/include/asm/ftrace.h
@@ -6,6 +6,10 @@
#ifndef _ASM_LOONGARCH_FTRACE_H
#define _ASM_LOONGARCH_FTRACE_H

+#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 713b4996bfac..9e7ac91d524d 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)
@@ -195,6 +197,7 @@ 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 9f6718df1854..a12a1d213220 100644
--- a/arch/loongarch/include/asm/module.h
+++ b/arch/loongarch/include/asm/module.h
@@ -19,6 +19,9 @@ struct mod_section {
struct mod_arch_specific {
struct mod_section plt;
struct mod_section plt_idx;
+
+ /* for CONFIG_DYNAMIC_FTRACE */
+ struct plt_entry *ftrace_trampolines;
};

struct plt_entry {
@@ -38,7 +41,7 @@ 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 31c1c0db11a3..ecff54b81754 100644
--- a/arch/loongarch/include/asm/module.lds.h
+++ b/arch/loongarch/include/asm/module.lds.h
@@ -4,4 +4,5 @@ SECTIONS {
. = ALIGN(4);
.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 f538829312d7..dd37185d446e 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 6d498288977d..b75fc711f144 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>

@@ -67,6 +68,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
unsigned int i, num_plts = 0;
+ Elf_Shdr *tramp = NULL;

/*
* Find the empty .plt sections.
@@ -76,6 +78,8 @@ 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.plt.shdr) {
@@ -117,5 +121,12 @@ 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 638427ff0d51..a4e30eea5ff8 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>
@@ -17,6 +18,7 @@
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/kernel.h>
+#include <asm/inst.h>

static inline bool signed_imm_check(long val, unsigned int bit)
{
@@ -373,3 +375,48 @@ void *module_alloc(unsigned long size)
return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
GFP_KERNEL, PAGE_KERNEL, 0, NUMA_NO_NODE, __builtin_return_address(0));
}
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+static const Elf_Shdr *find_section(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
+ const char *name)
+{
+ const Elf_Shdr *s, *se;
+ const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
+
+ for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++) {
+ if (strcmp(name, secstrs + s->sh_name) == 0)
+ return s;
+ }
+
+ return NULL;
+}
+#endif
+
+static int module_init_ftrace_plt(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
+ struct module *mod)
+{
+#ifdef CONFIG_DYNAMIC_FTRACE
+ const Elf_Shdr *s;
+ struct plt_entry *ftrace_plts;
+
+ s = find_section(hdr, sechdrs, ".ftrace_trampoline");
+ if (!s)
+ return -ENOEXEC;
+
+ ftrace_plts = (void *)s->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)
+{
+ return module_init_ftrace_plt(hdr, sechdrs, mod);
+
+}
--
2.20.1

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