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Support modules with a lot of sections #280

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b1682ca
libkmod: Support 32 bit ELF section indices
stoeckmann Feb 15, 2025
947d14d
libkmod: Support large ELF section indices
stoeckmann Feb 15, 2025
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76 changes: 50 additions & 26 deletions libkmod/libkmod-elf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -52,11 +52,11 @@
struct {
struct {
uint64_t offset;
uint16_t count;
uint32_t count;
uint16_t entry_size;
} section;
struct {
uint16_t section; /* index of the strings section */
uint32_t section; /* index of the strings section */
uint64_t size;
uint64_t offset;
} strings;
Expand Down Expand Up @@ -203,28 +203,28 @@
* (offset 0 cannot be a valid section offset because ELF header is located there).
*/
static inline uint64_t elf_get_section_header_offset(const struct kmod_elf *elf,
uint16_t idx)
uint32_t idx)
{
assert(idx != SHN_UNDEF);
assert(idx < elf->header.section.count);
if (idx == SHN_UNDEF || idx >= elf->header.section.count) {
ELFDBG(elf, "invalid section number: %" PRIu16 ", last=%" PRIu16 "\n",
ELFDBG(elf, "invalid section number: %" PRIu32 ", last=%" PRIu32 "\n",
idx, elf->header.section.count);
return 0;
}
return elf->header.section.offset +
(uint64_t)(idx * elf->header.section.entry_size);
(uint64_t)idx * elf->header.section.entry_size;
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Not sure how easy is for the uint16_t * uint16_t overflow to trigger, but let's keep this change as separate commit.

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Since idx is changed in this PR to a uint32_t and the C standard would therefore use unsigned int for the result, it would be possible.

}

static inline int elf_get_section_info(const struct kmod_elf *elf, uint16_t idx,
static inline int elf_get_section_info(const struct kmod_elf *elf, uint32_t idx,
uint64_t *offset, uint64_t *size,
const char **name)
{
uint64_t nameoff;
uint64_t off = elf_get_section_header_offset(elf, idx);

if (off == 0) {
ELFDBG(elf, "no section at %" PRIu16 "\n", idx);
ELFDBG(elf, "no section at %" PRIu32 "\n", idx);

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goto fail;
}

Expand Down Expand Up @@ -258,7 +258,7 @@
*name = elf_get_mem(elf, elf->header.strings.offset + nameoff);

ELFDBG(elf,
"section=%" PRIu16 " is: offset=%" PRIu64 " size=%" PRIu64 " name=%s\n",
"section=%" PRIu32 " is: offset=%" PRIu64 " size=%" PRIu64 " name=%s\n",
idx, *offset, *size, *name);

return 0;
Expand All @@ -275,7 +275,7 @@
uint16_t found_sec = 0;
enum kmod_elf_section sec;

for (uint16_t i = 1; i < elf->header.section.count && found_sec != all_sec; i++) {
for (uint32_t i = 1; i < elf->header.section.count && found_sec != all_sec; i++) {
uint64_t off, size;
const char *n;
int err = elf_get_section_info(elf, i, &off, &size, &n);
Expand Down Expand Up @@ -338,22 +338,42 @@
elf->size = size;

#define READV(field) elf_get_uint(elf, offsetof(typeof(*hdr), field), sizeof(hdr->field))
#define READXV(field) \
elf_get_uint(elf, elf->header.section.offset + offsetof(typeof(*shdr), field), \
sizeof(shdr->field))

#define LOAD_HEADER \
elf->header.section.offset = READV(e_shoff); \
elf->header.section.count = READV(e_shnum); \
elf->header.section.entry_size = READV(e_shentsize); \
elf->header.strings.section = READV(e_shstrndx); \
elf->header.machine = READV(e_machine); \
if (elf->header.section.count == 0 || \
elf->header.strings.section == SHN_XINDEX) { \
if (!elf_range_valid(elf, elf->header.section.offset, shdr_size)) \
goto invalid; \
if (elf->header.section.count == 0) { \
uint64_t val = READXV(sh_size); \
if (val > UINT32_MAX) \
goto invalid; \
elf->header.section.count = val; \
} \
if (elf->header.strings.section == SHN_XINDEX) { \
elf->header.strings.section = READXV(sh_link); \
} \
}

#define LOAD_HEADER \
elf->header.section.offset = READV(e_shoff); \
elf->header.section.count = READV(e_shnum); \
elf->header.section.entry_size = READV(e_shentsize); \
elf->header.strings.section = READV(e_shstrndx); \
elf->header.machine = READV(e_machine)
if (elf->x32) {
Elf32_Ehdr *hdr;
Elf32_Shdr *shdr;

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shdr_size = sizeof(Elf32_Shdr);
if (!elf_range_valid(elf, 0, shdr_size))
goto invalid;
LOAD_HEADER;
} else {
Elf64_Ehdr *hdr;
Elf64_Shdr *shdr;

shdr_size = sizeof(Elf64_Shdr);
if (!elf_range_valid(elf, 0, shdr_size))
Expand All @@ -364,8 +384,8 @@
#undef READV

ELFDBG(elf,
"section: offset=%" PRIu64 " count=%" PRIu16 " entry_size=%" PRIu16
" strings index=%" PRIu16 "\n",
"section: offset=%" PRIu64 " count=%" PRIu32 " entry_size=%" PRIu16
" strings index=%" PRIu32 "\n",
elf->header.section.offset, elf->header.section.count,
elf->header.section.entry_size, elf->header.strings.section);

Expand All @@ -374,7 +394,11 @@
elf->header.section.entry_size, shdr_size);
goto invalid;
}
shdrs_size = shdr_size * elf->header.section.count;
if (umulsz_overflow(shdr_size, elf->header.section.count, &shdrs_size)) {
ELFDBG(elf, "sections too large: %zu * %" PRIu32 "\n", shdr_size,
elf->header.section.count);
goto invalid;

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}
if (!elf_range_valid(elf, elf->header.section.offset, shdrs_size))
goto invalid;

Expand Down Expand Up @@ -412,13 +436,13 @@
}

/*
* Returns section index on success, negative value otherwise.
* Returns section index on success, zero otherwise.
* On success, sec_off and sec_size are range checked and valid.
*/
int kmod_elf_get_section(const struct kmod_elf *elf, const char *section,
uint64_t *sec_off, uint64_t *sec_size)
uint32_t kmod_elf_get_section(const struct kmod_elf *elf, const char *section,
uint64_t *sec_off, uint64_t *sec_size)
{
uint16_t i;
uint32_t i;

*sec_off = 0;
*sec_size = 0;
Expand All @@ -437,7 +461,7 @@
return i;
}

return -ENODATA;
return 0;
}

/* array will be allocated with strings in a single malloc, just free *array */
Expand Down Expand Up @@ -596,11 +620,11 @@
uint64_t off, size;
const void *buf;
/* the off and size values are not used, supply them as dummies */
int idx = kmod_elf_get_section(elf, "__versions", &off, &size);
uint32_t idx = kmod_elf_get_section(elf, "__versions", &off, &size);
uint64_t val;

if (idx < 0)
return idx == -ENODATA ? 0 : idx;
if (idx == 0)
return 0;

off = elf_get_section_header_offset(elf, idx);

Expand Down
2 changes: 1 addition & 1 deletion libkmod/libkmod-internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,7 @@ _must_check_ _nonnull_all_ const void *kmod_elf_strip(const struct kmod_elf *elf
* Debug mock lib need to find section ".gnu.linkonce.this_module" in order to
* get modname
*/
_must_check_ _nonnull_all_ int kmod_elf_get_section(const struct kmod_elf *elf, const char *section, uint64_t *sec_off, uint64_t *sec_size);
_must_check_ _nonnull_all_ uint32_t kmod_elf_get_section(const struct kmod_elf *elf, const char *section, uint64_t *sec_off, uint64_t *sec_size);

/* libkmod-signature.c */
struct kmod_signature_info {
Expand Down
5 changes: 3 additions & 2 deletions testsuite/init_module.c
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,7 @@ long init_module(void *mem, unsigned long len, const char *args)
struct kmod_elf *elf;
struct mod *mod;
const void *buf;
uint32_t idx;
uint64_t off;
uint64_t bufsize;
int err;
Expand All @@ -238,12 +239,12 @@ long init_module(void *mem, unsigned long len, const char *args)
if (elf == NULL)
return 0;

err = kmod_elf_get_section(elf, ".gnu.linkonce.this_module", &off, &bufsize);
idx = kmod_elf_get_section(elf, ".gnu.linkonce.this_module", &off, &bufsize);
buf = (const char *)kmod_elf_get_memory(elf) + off;
kmod_elf_unref(elf);

/* We couldn't parse the ELF file. Just exit as if it was successful */
if (err < 0)
if (idx == 0)
return 0;

/* We need to open both 32 and 64 bits module - hack! */
Expand Down