[PATCH] LoongArch: module: Use got/plt section indices for relocations

From: Huacai Chen
Date: Wed Nov 23 2022 - 03:21:16 EST

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Instead of saving a pointer to the .got, .plt and .plt_idx sections to
apply {got,plt}-based relocations, save and use their section indices
instead.

The mod->arch.{core,init}.{got,plt} pointers were problematic for live-
patch because they pointed within temporary section headers (provided by
the module loader via info->sechdrs) that would be freed after module
load. Since livepatch modules may need to apply relocations post-module-
load (for example, to patch a module that is loaded later), using section
indices to offset into the section headers (instead of accessing them
through a saved pointer) allows livepatch modules on LoongArch to pass
in their own copy of the section headers to apply_relocate_add() to
apply delayed relocations.

The method used is same as commit c8ebf64eab743 ("arm64/module: use plt
section indices for relocations").

Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
arch/loongarch/include/asm/module.h | 22 +++++-----
arch/loongarch/kernel/module-sections.c | 54 +++++++++++++------------
arch/loongarch/kernel/module.c | 39 ++++++++++++------
3 files changed, 68 insertions(+), 47 deletions(-)

diff --git a/arch/loongarch/include/asm/module.h b/arch/loongarch/include/asm/module.h
index b29b19a46f42..60dc62a1146e 100644
--- a/arch/loongarch/include/asm/module.h
+++ b/arch/loongarch/include/asm/module.h
@@ -11,7 +11,7 @@
#define RELA_STACK_DEPTH 16

struct mod_section {
- Elf_Shdr *shdr;
+ int shndx;
int num_entries;
int max_entries;
};
@@ -37,8 +37,8 @@ struct plt_idx_entry {
Elf_Addr symbol_addr;
};

-Elf_Addr module_emit_got_entry(struct module *mod, Elf_Addr val);
-Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Addr val);
+Elf_Addr module_emit_got_entry(struct module *mod, Elf_Shdr *sechdrs, Elf_Addr val);
+Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Shdr *sechdrs, Elf_Addr val);

static inline struct got_entry emit_got_entry(Elf_Addr val)
{
@@ -62,10 +62,10 @@ static inline struct plt_idx_entry emit_plt_idx_entry(unsigned long val)
return (struct plt_idx_entry) { val };
}

-static inline int get_plt_idx(unsigned long val, const struct mod_section *sec)
+static inline int get_plt_idx(unsigned long val, Elf_Shdr *sechdrs, const struct mod_section *sec)
{
int i;
- struct plt_idx_entry *plt_idx = (struct plt_idx_entry *)sec->shdr->sh_addr;
+ struct plt_idx_entry *plt_idx = (struct plt_idx_entry *)sechdrs[sec->shndx].sh_addr;

for (i = 0; i < sec->num_entries; i++) {
if (plt_idx[i].symbol_addr == val)
@@ -76,11 +76,12 @@ static inline int get_plt_idx(unsigned long val, const struct mod_section *sec)
}

static inline struct plt_entry *get_plt_entry(unsigned long val,
- const struct mod_section *sec_plt,
- const struct mod_section *sec_plt_idx)
+ Elf_Shdr *sechdrs,
+ const struct mod_section *sec_plt,
+ const struct mod_section *sec_plt_idx)
{
- int plt_idx = get_plt_idx(val, sec_plt_idx);
- struct plt_entry *plt = (struct plt_entry *)sec_plt->shdr->sh_addr;
+ int plt_idx = get_plt_idx(val, sechdrs, sec_plt_idx);
+ struct plt_entry *plt = (struct plt_entry *)sechdrs[sec_plt->shndx].sh_addr;

if (plt_idx < 0)
return NULL;
@@ -89,10 +90,11 @@ static inline struct plt_entry *get_plt_entry(unsigned long val,
}

static inline struct got_entry *get_got_entry(Elf_Addr val,
+ Elf_Shdr *sechdrs,
const struct mod_section *sec)
{
- struct got_entry *got = (struct got_entry *)sec->shdr->sh_addr;
int i;
+ struct got_entry *got = (struct got_entry *)sechdrs[sec->shndx].sh_addr;

for (i = 0; i < sec->num_entries; i++)
if (got[i].symbol_addr == val)
diff --git a/arch/loongarch/kernel/module-sections.c b/arch/loongarch/kernel/module-sections.c
index d296a70b758f..13d9a427325a 100644
--- a/arch/loongarch/kernel/module-sections.c
+++ b/arch/loongarch/kernel/module-sections.c
@@ -7,17 +7,17 @@
#include <linux/kernel.h>
#include <linux/module.h>

-Elf_Addr module_emit_got_entry(struct module *mod, Elf_Addr val)
+Elf_Addr module_emit_got_entry(struct module *mod, Elf_Shdr *sechdrs, Elf_Addr val)
{
struct mod_section *got_sec = &mod->arch.got;
int i = got_sec->num_entries;
- struct got_entry *got = get_got_entry(val, got_sec);
+ struct got_entry *got = get_got_entry(val, sechdrs, got_sec);

if (got)
return (Elf_Addr)got;

/* There is no GOT entry for val yet, create a new one. */
- got = (struct got_entry *)got_sec->shdr->sh_addr;
+ got = (struct got_entry *)sechdrs[got_sec->shndx].sh_addr;
got[i] = emit_got_entry(val);

got_sec->num_entries++;
@@ -33,12 +33,12 @@ Elf_Addr module_emit_got_entry(struct module *mod, Elf_Addr val)
return (Elf_Addr)&got[i];
}

-Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Addr val)
+Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Shdr *sechdrs, Elf_Addr val)
{
int nr;
struct mod_section *plt_sec = &mod->arch.plt;
struct mod_section *plt_idx_sec = &mod->arch.plt_idx;
- struct plt_entry *plt = get_plt_entry(val, plt_sec, plt_idx_sec);
+ struct plt_entry *plt = get_plt_entry(val, sechdrs, plt_sec, plt_idx_sec);
struct plt_idx_entry *plt_idx;

if (plt)
@@ -47,9 +47,9 @@ Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Addr val)
nr = plt_sec->num_entries;

/* There is no duplicate entry, create a new one */
- plt = (struct plt_entry *)plt_sec->shdr->sh_addr;
+ plt = (struct plt_entry *)sechdrs[plt_sec->shndx].sh_addr;
plt[nr] = emit_plt_entry(val);
- plt_idx = (struct plt_idx_entry *)plt_idx_sec->shdr->sh_addr;
+ plt_idx = (struct plt_idx_entry *)sechdrs[plt_idx_sec->shndx].sh_addr;
plt_idx[nr] = emit_plt_idx_entry(val);

plt_sec->num_entries++;
@@ -103,28 +103,29 @@ 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 *got_sec, *plt_sec, *plt_idx_sec;

/*
* Find the empty .plt sections.
*/
for (i = 0; i < ehdr->e_shnum; i++) {
if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
- mod->arch.got.shdr = sechdrs + i;
+ mod->arch.got.shndx = i;
else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
- mod->arch.plt.shdr = sechdrs + i;
+ mod->arch.plt.shndx = i;
else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt.idx"))
- mod->arch.plt_idx.shdr = sechdrs + i;
+ mod->arch.plt_idx.shndx = i;
}

- if (!mod->arch.got.shdr) {
+ if (!mod->arch.got.shndx) {
pr_err("%s: module GOT section(s) missing\n", mod->name);
return -ENOEXEC;
}
- if (!mod->arch.plt.shdr) {
+ if (!mod->arch.plt.shndx) {
pr_err("%s: module PLT section(s) missing\n", mod->name);
return -ENOEXEC;
}
- if (!mod->arch.plt_idx.shdr) {
+ if (!mod->arch.plt_idx.shndx) {
pr_err("%s: module PLT.IDX section(s) missing\n", mod->name);
return -ENOEXEC;
}
@@ -145,24 +146,27 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
count_max_entries(relas, num_rela, &num_plts, &num_gots);
}

- mod->arch.got.shdr->sh_type = SHT_NOBITS;
- mod->arch.got.shdr->sh_flags = SHF_ALLOC;
- mod->arch.got.shdr->sh_addralign = L1_CACHE_BYTES;
- mod->arch.got.shdr->sh_size = (num_gots + 1) * sizeof(struct got_entry);
+ got_sec = sechdrs + mod->arch.got.shndx;
+ got_sec->sh_type = SHT_NOBITS;
+ got_sec->sh_flags = SHF_ALLOC;
+ got_sec->sh_addralign = L1_CACHE_BYTES;
+ got_sec->sh_size = (num_gots + 1) * sizeof(struct got_entry);
mod->arch.got.num_entries = 0;
mod->arch.got.max_entries = num_gots;

- mod->arch.plt.shdr->sh_type = SHT_NOBITS;
- mod->arch.plt.shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
- mod->arch.plt.shdr->sh_addralign = L1_CACHE_BYTES;
- mod->arch.plt.shdr->sh_size = (num_plts + 1) * sizeof(struct plt_entry);
+ plt_sec = sechdrs + mod->arch.plt.shndx;
+ plt_sec->sh_type = SHT_NOBITS;
+ plt_sec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+ plt_sec->sh_addralign = L1_CACHE_BYTES;
+ plt_sec->sh_size = (num_plts + 1) * sizeof(struct plt_entry);
mod->arch.plt.num_entries = 0;
mod->arch.plt.max_entries = num_plts;

- mod->arch.plt_idx.shdr->sh_type = SHT_NOBITS;
- mod->arch.plt_idx.shdr->sh_flags = SHF_ALLOC;
- mod->arch.plt_idx.shdr->sh_addralign = L1_CACHE_BYTES;
- mod->arch.plt_idx.shdr->sh_size = (num_plts + 1) * sizeof(struct plt_idx_entry);
+ plt_idx_sec = sechdrs + mod->arch.plt_idx.shndx;
+ plt_idx_sec->sh_type = SHT_NOBITS;
+ plt_idx_sec->sh_flags = SHF_ALLOC;
+ plt_idx_sec->sh_addralign = L1_CACHE_BYTES;
+ plt_idx_sec->sh_size = (num_plts + 1) * sizeof(struct plt_idx_entry);
mod->arch.plt_idx.num_entries = 0;
mod->arch.plt_idx.max_entries = num_plts;

diff --git a/arch/loongarch/kernel/module.c b/arch/loongarch/kernel/module.c
index 825fcf77f9e7..899dc677cec3 100644
--- a/arch/loongarch/kernel/module.c
+++ b/arch/loongarch/kernel/module.c
@@ -99,16 +99,17 @@ static int apply_r_larch_sop_push_dup(struct module *mod, u32 *location, Elf_Add
return 0;
}

-static int apply_r_larch_sop_push_plt_pcrel(struct module *mod, u32 *location, Elf_Addr v,
+static int apply_r_larch_sop_push_plt_pcrel(struct module *mod,
+ Elf_Shdr *sechdrs, u32 *location, Elf_Addr v,
s64 *rela_stack, size_t *rela_stack_top, unsigned int type)
{
ptrdiff_t offset = (void *)v - (void *)location;

if (offset >= SZ_128M)
- v = module_emit_plt_entry(mod, v);
+ v = module_emit_plt_entry(mod, sechdrs, v);

if (offset < -SZ_128M)
- v = module_emit_plt_entry(mod, v);
+ v = module_emit_plt_entry(mod, sechdrs, v);

return apply_r_larch_sop_push_pcrel(mod, location, v, rela_stack, rela_stack_top, type);
}
@@ -272,17 +273,18 @@ static int apply_r_larch_add_sub(struct module *mod, u32 *location, Elf_Addr v,
}
}

-static int apply_r_larch_b26(struct module *mod, u32 *location, Elf_Addr v,
+static int apply_r_larch_b26(struct module *mod,
+ Elf_Shdr *sechdrs, u32 *location, Elf_Addr v,
s64 *rela_stack, size_t *rela_stack_top, unsigned int type)
{
ptrdiff_t offset = (void *)v - (void *)location;
union loongarch_instruction *insn = (union loongarch_instruction *)location;

if (offset >= SZ_128M)
- v = module_emit_plt_entry(mod, v);
+ v = module_emit_plt_entry(mod, sechdrs, v);

if (offset < -SZ_128M)
- v = module_emit_plt_entry(mod, v);
+ v = module_emit_plt_entry(mod, sechdrs, v);

offset = (void *)v - (void *)location;

@@ -339,10 +341,11 @@ static int apply_r_larch_pcala(struct module *mod, u32 *location, Elf_Addr v,
return 0;
}

-static int apply_r_larch_got_pc(struct module *mod, u32 *location, Elf_Addr v,
+static int apply_r_larch_got_pc(struct module *mod,
+ Elf_Shdr *sechdrs, u32 *location, Elf_Addr v,
s64 *rela_stack, size_t *rela_stack_top, unsigned int type)
{
- Elf_Addr got = module_emit_got_entry(mod, v);
+ Elf_Addr got = module_emit_got_entry(mod, sechdrs, v);

if (!got)
return -EINVAL;
@@ -387,13 +390,10 @@ static reloc_rela_handler reloc_rela_handlers[] = {
[R_LARCH_SOP_PUSH_PCREL] = apply_r_larch_sop_push_pcrel,
[R_LARCH_SOP_PUSH_ABSOLUTE] = apply_r_larch_sop_push_absolute,
[R_LARCH_SOP_PUSH_DUP] = apply_r_larch_sop_push_dup,
- [R_LARCH_SOP_PUSH_PLT_PCREL] = apply_r_larch_sop_push_plt_pcrel,
[R_LARCH_SOP_SUB ... R_LARCH_SOP_IF_ELSE] = apply_r_larch_sop,
[R_LARCH_SOP_POP_32_S_10_5 ... R_LARCH_SOP_POP_32_U] = apply_r_larch_sop_imm_field,
[R_LARCH_ADD32 ... R_LARCH_SUB64] = apply_r_larch_add_sub,
- [R_LARCH_B26] = apply_r_larch_b26,
[R_LARCH_PCALA_HI20...R_LARCH_PCALA64_HI12] = apply_r_larch_pcala,
- [R_LARCH_GOT_PC_HI20...R_LARCH_GOT_PC_LO12] = apply_r_larch_got_pc,
};

int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
@@ -444,7 +444,22 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
sym->st_value, rel[i].r_addend, (u64)location);

v = sym->st_value + rel[i].r_addend;
- err = handler(mod, location, v, rela_stack, &rela_stack_top, type);
+ switch (type) {
+ case R_LARCH_B26:
+ err = apply_r_larch_b26(mod, sechdrs, location,
+ v, rela_stack, &rela_stack_top, type);
+ break;
+ case R_LARCH_GOT_PC_HI20...R_LARCH_GOT_PC_LO12:
+ err = apply_r_larch_got_pc(mod, sechdrs, location,
+ v, rela_stack, &rela_stack_top, type);
+ break;
+ case R_LARCH_SOP_PUSH_PLT_PCREL:
+ err = apply_r_larch_sop_push_plt_pcrel(mod, sechdrs, location,
+ v, rela_stack, &rela_stack_top, type);
+ break;
+ default:
+ err = handler(mod, location, v, rela_stack, &rela_stack_top, type);
+ }
if (err)
return err;
}
--
2.31.1

Next message: Tommaso Merciai: "Re: [PATCH] media: imx: remove code for non-existing config IMX_GPT_ICAP"
Previous message: Krzysztof Kozlowski: "Re: (subset) [PATCH 06/20] arm64: dts: Update cache properties for exynos"
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