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module: Factor out elf_validity_cache_index_mod

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Centralize .gnu.linkonce.this_module detection and property validation.

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 23:16:40 +00:00 committed by Luis Chamberlain
parent fbc0e4e482
commit 0be41a9367
1 changed files with 67 additions and 62 deletions
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129
kernel/module/main.c
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@ -1919,6 +1919,68 @@ static int elf_validity_cache_index_info(struct load_info *info)
return 0;
}
/**
* elf_validity_cache_index_mod() - Validates and caches this_module section
* @info: Load info to cache this_module on.
* Must have &load_info->sechdrs and &load_info->secstrings populated
*
* The ".gnu.linkonce.this_module" ELF section is special. It is what modpost
* uses to refer to __this_module and let's use rely on THIS_MODULE to point
* to &__this_module properly. The kernel's modpost declares it on each
* modules's *.mod.c file. If the struct module of the kernel changes a full
* kernel rebuild is required.
*
* We have a few expectations for this special section, this function
* validates all this for us:
*
* * The section has contents
* * The section is unique
* * We expect the kernel to always have to allocate it: SHF_ALLOC
* * The section size must match the kernel's run time's struct module
* size
*
* If all checks pass, the index will be cached in &load_info->index.mod
*
* Return: %0 on validation success, %-ENOEXEC on failure
*/
static int elf_validity_cache_index_mod(struct load_info *info)
{
Elf_Shdr *shdr;
int mod_idx;
mod_idx = find_any_unique_sec(info, ".gnu.linkonce.this_module");
if (mod_idx <= 0) {
pr_err("module %s: Exactly one .gnu.linkonce.this_module section must exist.\n",
info->name ?: "(missing .modinfo section or name field)");
return -ENOEXEC;
}
shdr = &info->sechdrs[mod_idx];
if (shdr->sh_type == SHT_NOBITS) {
pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n",
info->name ?: "(missing .modinfo section or name field)");
return -ENOEXEC;
}
if (!(shdr->sh_flags & SHF_ALLOC)) {
pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n",
info->name ?: "(missing .modinfo section or name field)");
return -ENOEXEC;
}
if (shdr->sh_size != sizeof(struct module)) {
pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n",
info->name ?: "(missing .modinfo section or name field)");
return -ENOEXEC;
}
info->index.mod = mod_idx;
return 0;
}
/*
* Check userspace passed ELF module against our expectations, and cache
* useful variables for further processing as we go.
@ -1944,7 +2006,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
unsigned int i;
Elf_Shdr *shdr;
int err;
unsigned int num_mod_secs = 0, mod_idx;
unsigned int num_sym_secs = 0, sym_idx;
err = elf_validity_cache_sechdrs(info);
@ -1954,16 +2015,15 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
if (err < 0)
return err;
err = elf_validity_cache_index_info(info);
if (err < 0)
return err;
err = elf_validity_cache_index_mod(info);
if (err < 0)
return err;
for (i = 1; i < info->hdr->e_shnum; i++) {
shdr = &info->sechdrs[i];
switch (shdr->sh_type) {
case SHT_NULL:
case SHT_NOBITS:
continue;
case SHT_SYMTAB:
if (shdr->sh_type == SHT_SYMTAB) {
if (shdr->sh_link == SHN_UNDEF
|| shdr->sh_link >= info->hdr->e_shnum) {
pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
@ -1973,14 +2033,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
}
num_sym_secs++;
sym_idx = i;
fallthrough;
default:
if (strcmp(info->secstrings + shdr->sh_name,
".gnu.linkonce.this_module") == 0) {
num_mod_secs++;
mod_idx = i;
}
break;
}
}
@ -1996,55 +2048,8 @@ static int elf_validity_cache_copy(struct load_info *info, int flags)
info->index.str = shdr->sh_link;
info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset;
/*
* The ".gnu.linkonce.this_module" ELF section is special. It is
* what modpost uses to refer to __this_module and let's use rely
* on THIS_MODULE to point to &__this_module properly. The kernel's
* modpost declares it on each modules's *.mod.c file. If the struct
* module of the kernel changes a full kernel rebuild is required.
*
* We have a few expectaions for this special section, the following
* code validates all this for us:
*
* o Only one section must exist
* o We expect the kernel to always have to allocate it: SHF_ALLOC
* o The section size must match the kernel's run time's struct module
* size
*/
if (num_mod_secs != 1) {
pr_err("module %s: Only one .gnu.linkonce.this_module section must exist.\n",
info->name ?: "(missing .modinfo section or name field)");
goto no_exec;
}
shdr = &info->sechdrs[mod_idx];
/*
* This is already implied on the switch above, however let's be
* pedantic about it.
*/
if (shdr->sh_type == SHT_NOBITS) {
pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n",
info->name ?: "(missing .modinfo section or name field)");
goto no_exec;
}
if (!(shdr->sh_flags & SHF_ALLOC)) {
pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n",
info->name ?: "(missing .modinfo section or name field)");
goto no_exec;
}
if (shdr->sh_size != sizeof(struct module)) {
pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n",
info->name ?: "(missing .modinfo section or name field)");
goto no_exec;
}
info->index.mod = mod_idx;
/* This is temporary: point mod into copy of data. */
info->mod = (void *)info->hdr + shdr->sh_offset;
info->mod = (void *)info->hdr + info->sechdrs[info->index.mod].sh_offset;
/*
* If we didn't load the .modinfo 'name' field earlier, fall back to