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module: Factor out elf_validity_ehdr

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Factor out verification of the ELF header and document what is checked.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
This commit is contained in:
Matthew Maurer 2024-10-15 23:16:36 +00:00 committed by Luis Chamberlain
parent f439221621
commit 90f8f312db
1 changed files with 47 additions and 23 deletions
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70
kernel/module/main.c
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@ -1664,6 +1664,50 @@ static int validate_section_offset(const struct load_info *info, Elf_Shdr *shdr)
return 0;
}
/**
* elf_validity_ehdr() - Checks an ELF header for module validity
* @info: Load info containing the ELF header to check
*
* Checks whether an ELF header could belong to a valid module. Checks:
*
* * ELF header is within the data the user provided
* * ELF magic is present
* * It is relocatable (not final linked, not core file, etc.)
* * The header's machine type matches what the architecture expects.
* * Optional arch-specific hook for other properties
* - module_elf_check_arch() is currently only used by PPC to check
* ELF ABI version, but may be used by others in the future.
*
* Return: %0 if valid, %-ENOEXEC on failure.
*/
static int elf_validity_ehdr(const struct load_info *info)
{
if (info->len < sizeof(*(info->hdr))) {
pr_err("Invalid ELF header len %lu\n", info->len);
return -ENOEXEC;
}
if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
return -ENOEXEC;
}
if (info->hdr->e_type != ET_REL) {
pr_err("Invalid ELF header type: %u != %u\n",
info->hdr->e_type, ET_REL);
return -ENOEXEC;
}
if (!elf_check_arch(info->hdr)) {
pr_err("Invalid architecture in ELF header: %u\n",
info->hdr->e_machine);
return -ENOEXEC;
}
if (!module_elf_check_arch(info->hdr)) {
pr_err("Invalid module architecture in ELF header: %u\n",
info->hdr->e_machine);
return -ENOEXEC;
}
return 0;
}
/*
* Check userspace passed ELF module against our expectations, and cache
* useful variables for further processing as we go.
@ -1693,30 +1737,10 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
unsigned int num_info_secs = 0, info_idx;
unsigned int num_sym_secs = 0, sym_idx;
if (info->len < sizeof(*(info->hdr))) {
pr_err("Invalid ELF header len %lu\n", info->len);
goto no_exec;
}
err = elf_validity_ehdr(info);
if (err < 0)
return err;
if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
goto no_exec;
}
if (info->hdr->e_type != ET_REL) {
pr_err("Invalid ELF header type: %u != %u\n",
info->hdr->e_type, ET_REL);
goto no_exec;
}
if (!elf_check_arch(info->hdr)) {
pr_err("Invalid architecture in ELF header: %u\n",
info->hdr->e_machine);
goto no_exec;
}
if (!module_elf_check_arch(info->hdr)) {
pr_err("Invalid module architecture in ELF header: %u\n",
info->hdr->e_machine);
goto no_exec;
}
if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
pr_err("Invalid ELF section header size\n");
goto no_exec;