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libkmod: store common section off/size and use them
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Currently, we repeatedly loop over the elf headers looking for five well
known sections. Just do it once in kmod_elf_new() and reuse the data as
needed.

Note, that not all sections are guaranteed to be available, so calloc()
the struct kmod_elf, so we don't rely on garbage data later on.

Signed-off-by: Emil Velikov <[email protected]>
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@evelikov
evelikov committed Oct 24, 2024
1 parent 6e84030 commit 030cf3f
Showing 1 changed file with 85 additions and 29 deletions.
114 changes: 85 additions & 29 deletions libkmod/libkmod-elf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,15 @@ struct kmod_modversion64 {
char name[64 - sizeof(uint64_t)];
};

enum kmod_elf_section {
KMOD_ELF_SECTION_KSYMTAB,
KMOD_ELF_SECTION_MODINFO,
KMOD_ELF_SECTION_STRTAB,
KMOD_ELF_SECTION_SYMTAB,
KMOD_ELF_SECTION_VERSIONS,
KMOD_ELF_SECTION_MAX,
};

struct kmod_elf {
const uint8_t *memory;
uint64_t size;
Expand All @@ -45,6 +54,10 @@ struct kmod_elf {
} strings;
uint16_t machine;
} header;
struct {
uint64_t offset;
uint64_t size;
} sections[KMOD_ELF_SECTION_MAX];
};

//#undef ENABLE_ELFDBG
Expand Down Expand Up @@ -248,6 +261,42 @@ static inline int elf_get_section_info(const struct kmod_elf *elf, uint16_t idx,
return -EINVAL;
}

static void kmod_elf_save_sections(struct kmod_elf *elf)
{
for (uint16_t i = 1; i < elf->header.section.count; i++) {
uint64_t off, size;
const char *n;
int err = elf_get_section_info(elf, i, &off, &size, &n);
if (err < 0)
continue;
if (streq("__ksymtab_strings", n)) {
elf->sections[KMOD_ELF_SECTION_KSYMTAB].offset = off;
elf->sections[KMOD_ELF_SECTION_KSYMTAB].size = size;
continue;
}
if (streq(".modinfo", n)) {
elf->sections[KMOD_ELF_SECTION_MODINFO].offset = off;
elf->sections[KMOD_ELF_SECTION_MODINFO].size = size;
continue;
}
if (streq(".strtab", n)) {
elf->sections[KMOD_ELF_SECTION_STRTAB].offset = off;
elf->sections[KMOD_ELF_SECTION_STRTAB].size = size;
continue;
}
if (streq(".symtab", n)) {
elf->sections[KMOD_ELF_SECTION_SYMTAB].offset = off;
elf->sections[KMOD_ELF_SECTION_SYMTAB].size = size;
continue;
}
if (streq("__versions", n)) {
elf->sections[KMOD_ELF_SECTION_VERSIONS].offset = off;
elf->sections[KMOD_ELF_SECTION_VERSIONS].size = size;
continue;
}
}
}

struct kmod_elf *kmod_elf_new(const void *memory, off_t size)
{
struct kmod_elf *elf;
Expand All @@ -266,7 +315,7 @@ struct kmod_elf *kmod_elf_new(const void *memory, off_t size)
return NULL;
}

elf = malloc(sizeof(struct kmod_elf));
elf = calloc(1, sizeof(struct kmod_elf));
if (elf == NULL) {
return NULL;
}
Expand Down Expand Up @@ -339,6 +388,7 @@ struct kmod_elf *kmod_elf_new(const void *memory, off_t size)
}
}

kmod_elf_save_sections(elf);
return elf;

invalid:
Expand Down Expand Up @@ -394,13 +444,13 @@ int kmod_elf_get_modinfo_strings(const struct kmod_elf *elf, char ***array)
uint64_t off, size;
const char *strings;
char *s, **a;
int err;

*array = NULL;

err = kmod_elf_get_section(elf, ".modinfo", &off, &size);
if (err < 0)
return err;
off = elf->sections[KMOD_ELF_SECTION_MODINFO].offset;
size = elf->sections[KMOD_ELF_SECTION_MODINFO].size;
if (off == 0)
return -ENODATA;

strings = elf_get_mem(elf, off);

Expand Down Expand Up @@ -470,7 +520,7 @@ int kmod_elf_get_modversions(const struct kmod_elf *elf, struct kmod_modversion
size_t off, offcrc;
uint64_t sec_off, size;
struct kmod_modversion *a;
int i, count, err;
int i, count;
#define MODVERSION_SEC_SIZE (sizeof(struct kmod_modversion64))

assert_cc(sizeof(struct kmod_modversion64) == sizeof(struct kmod_modversion32));
Expand All @@ -482,9 +532,10 @@ int kmod_elf_get_modversions(const struct kmod_elf *elf, struct kmod_modversion

*array = NULL;

err = kmod_elf_get_section(elf, "__versions", &sec_off, &size);
if (err < 0)
return err;
sec_off = elf->sections[KMOD_ELF_SECTION_VERSIONS].offset;
size = elf->sections[KMOD_ELF_SECTION_VERSIONS].size;
if (sec_off == 0)
return -ENODATA;

if (size == 0)
return 0;
Expand Down Expand Up @@ -543,11 +594,11 @@ static int elf_strip_vermagic(const struct kmod_elf *elf, uint8_t *changed)
{
uint64_t i, sec_off, size;
const char *strings;
int err;

err = kmod_elf_get_section(elf, ".modinfo", &sec_off, &size);
if (err < 0)
return err == -ENODATA ? 0 : err;
sec_off = elf->sections[KMOD_ELF_SECTION_MODINFO].offset;
size = elf->sections[KMOD_ELF_SECTION_MODINFO].size;
if (sec_off == 0)
return 0;
strings = elf_get_mem(elf, sec_off);

/* skip zero padding */
Expand Down Expand Up @@ -628,14 +679,15 @@ static int kmod_elf_get_symbols_symtab(const struct kmod_elf *elf,
uint64_t i, last, off, size;
const char *strings;
struct kmod_modversion *a;
int count, err;
int count;
size_t total_size;

*array = NULL;

err = kmod_elf_get_section(elf, "__ksymtab_strings", &off, &size);
if (err < 0)
return err;
off = elf->sections[KMOD_ELF_SECTION_KSYMTAB].offset;
size = elf->sections[KMOD_ELF_SECTION_KSYMTAB].size;
if (off == 0)
return -ENODATA;
strings = elf_get_mem(elf, off);

/* skip zero padding */
Expand Down Expand Up @@ -735,16 +787,17 @@ int kmod_elf_get_symbols(const struct kmod_elf *elf, struct kmod_modversion **ar
uint64_t strtablen, symtablen, str_sec_off, sym_sec_off, str_off, sym_off;
struct kmod_modversion *a;
size_t i, count, symcount, symlen;
int err;

err = kmod_elf_get_section(elf, ".strtab", &str_sec_off, &strtablen);
if (err < 0) {
str_sec_off = elf->sections[KMOD_ELF_SECTION_STRTAB].offset;
strtablen = elf->sections[KMOD_ELF_SECTION_STRTAB].size;
if (str_sec_off == 0) {
ELFDBG(elf, "no .strtab found.\n");
goto fallback;
}

err = kmod_elf_get_section(elf, ".symtab", &sym_sec_off, &symtablen);
if (err < 0) {
sym_sec_off = elf->sections[KMOD_ELF_SECTION_SYMTAB].offset;
symtablen = elf->sections[KMOD_ELF_SECTION_SYMTAB].size;
if (sym_sec_off == 0) {
ELFDBG(elf, "no .symtab found.\n");
goto fallback;
}
Expand Down Expand Up @@ -897,13 +950,14 @@ int kmod_elf_get_dependency_symbols(const struct kmod_elf *elf,
uint64_t str_sec_off, sym_sec_off;
struct kmod_modversion *a;
size_t verlen, symlen, crclen;
int i, count, symcount, vercount, err;
int i, count, symcount, vercount;
bool handle_register_symbols;
uint8_t *visited_versions;
uint64_t *symcrcs;

err = kmod_elf_get_section(elf, "__versions", &ver_off, &versionslen);
if (err < 0) {
ver_off = elf->sections[KMOD_ELF_SECTION_VERSIONS].offset;
versionslen = elf->sections[KMOD_ELF_SECTION_VERSIONS].size;
if (ver_off == 0) {
versionslen = 0;
verlen = 0;
crclen = 0;
Expand All @@ -927,14 +981,16 @@ int kmod_elf_get_dependency_symbols(const struct kmod_elf *elf,
}
}

err = kmod_elf_get_section(elf, ".strtab", &str_sec_off, &strtablen);
if (err < 0) {
str_sec_off = elf->sections[KMOD_ELF_SECTION_STRTAB].offset;
strtablen = elf->sections[KMOD_ELF_SECTION_STRTAB].size;
if (str_sec_off == 0) {
ELFDBG(elf, "no .strtab found.\n");
return -EINVAL;
}

err = kmod_elf_get_section(elf, ".symtab", &sym_sec_off, &symtablen);
if (err < 0) {
sym_sec_off = elf->sections[KMOD_ELF_SECTION_SYMTAB].offset;
symtablen = elf->sections[KMOD_ELF_SECTION_SYMTAB].size;
if (sym_sec_off == 0) {
ELFDBG(elf, "no .symtab found.\n");
return -EINVAL;
}
Expand Down

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