[PATCH v5 02/16] module: Factor out elf_validity_ehdr

[Matthew Maurer]

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

Signed-off-by: Matthew Maurer <mmau...@google.com>
---
 kernel/module/main.c | 70 +++++++++++++++++++++++++++++---------------
 1 file changed, 47 insertions(+), 23 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 1a2dd52147ba..59c977acfb44 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -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;
-- 
2.46.1.824.gd892dcdcdd-goog