@@ -1560,6 +1560,13 @@ static inline int get_section_entry_size(const struct section *sec,
return entry_size;
}
+/* Check if RELA entry has undefined or unchanged/not-included symbols. */
+static inline bool has_rela_undefined_symbol(const struct rela *rela)
+{
+ return (GELF_R_SYM(rela->rela.r_info) == STN_UNDEF) ||
+ (!rela->sym->include && (rela->sym->status == SAME));
+}
+
static int kpatch_section_has_undef_symbols(struct kpatch_elf *kelf,
const struct section *sec)
{
@@ -1579,8 +1586,7 @@ static int kpatch_section_has_undef_symbols(struct kpatch_elf *kelf,
continue;
}
- if ((GELF_R_SYM(rela->rela.r_info) == STN_UNDEF) ||
- (!rela->sym->include && rela->sym->status == SAME)) {
+ if (has_rela_undefined_symbol(rela)) {
log_normal("section %s has an entry with an undefined symbol: %s\n",
sec->name, rela->sym->name ?: "none");
return true;
@@ -1994,6 +2000,125 @@ static void livepatch_create_patches_sections(struct kpatch_elf *kelf,
}
+/*
+ * The patched ELF object file contains all sections and symbols as resulted
+ * from the compilation. However, certain symbols may not be copied over to
+ * the resulting object file, due to being unchanged or not included for other
+ * reasons.
+ * In such situation the resulting object file has the entire sections copied
+ * along (with all their entries unchanged), while some of the corresponding
+ * symbols are not copied along at all.
+ * This leads to having incorrect dummy (STN_UNDEF) entries in the final
+ * hotpatch ELF file.
+ * This functions removes all undefined entries of known size from both
+ * RELA and PROGBITS sections of the patched elf object.
+ */
+static void livepatch_strip_undefined_elements(struct kpatch_elf *kelf)
+{
+ struct section *sec;
+
+ list_for_each_entry(sec, &kelf->sections, list) {
+ struct rela *rela, *safe;
+ int src_offset = 0, dst_offset = 0;
+ int entry_size, align, aligned_size;
+ char *src, *dst;
+ LIST_HEAD(newrelas);
+
+ /* use RELA section to find all its undefined entries */
+ if (!is_rela_section(sec))
+ continue;
+
+ /* only known, fixed-size entries can be stripped */
+ entry_size = get_section_entry_size(sec->base, kelf);
+ if (entry_size == 0)
+ continue;
+
+ /* alloc buffer for new base section */
+ dst = malloc(sec->base->sh.sh_size);
+ if (!dst)
+ ERROR("malloc");
+
+ /*
+ * Iterate through all entries of a corresponding base section
+ * for this RELA section.
+ */
+ for ( src = sec->base->data->d_buf;
+ src_offset < sec->base->sh.sh_size;
+ src_offset += entry_size ) {
+ bool found_valid = false;
+
+ list_for_each_entry_safe(rela, safe, &sec->relas, list) {
+ /*
+ * Check all RELA elements looking for
+ * corresponding entry references.
+ */
+ if (rela->offset < src_offset ||
+ rela->offset >= src_offset + entry_size) {
+ continue;
+ }
+
+ /*
+ * Ignore all undefined (STN_UNDEF) or
+ * unchanged/not-included elements.
+ */
+ if (has_rela_undefined_symbol(rela)) {
+ log_normal("Found a STN_UNDEF symbol %s in section %s\n",
+ rela->sym->name, sec->name);
+ continue;
+ }
+
+ /*
+ * A correct match has been found, so move it
+ * to a new list. Original list will be destroyed
+ * along with the entire kelf object, so the
+ * reference must be preserved.
+ */
+ found_valid = true;
+ list_del(&rela->list);
+ list_add_tail(&rela->list, &newrelas);
+
+ rela->offset -= src_offset - dst_offset;
+ rela->rela.r_offset = rela->offset;
+ }
+
+ /* there is a valid RELA entry, so copy current entry */
+ if (found_valid) {
+ /* copy base section group */
+ memcpy(dst + dst_offset, src + src_offset, entry_size);
+ dst_offset += entry_size;
+ }
+ }
+
+ /* verify that entry_size is a divisor of aligned section size */
+ align = sec->base->sh.sh_addralign;
+ aligned_size = ((sec->base->sh.sh_size + align - 1) / align) * align;
+ if (src_offset != aligned_size) {
+ ERROR("group size mismatch for section %s\n",
+ sec->base->name);
+ }
+
+ if (!dst_offset) {
+ /* no changed or global functions referenced */
+ sec->status = sec->base->status = SAME;
+ sec->include = sec->base->include = 0;
+ free(dst);
+ continue;
+ }
+
+ /* overwrite with new relas list */
+ list_replace(&newrelas, &sec->relas);
+
+ /*
+ * Update text section data buf and size.
+ *
+ * The rela section's data buf and size will be
+ * regenerated in kpatch_rebuild_rela_section_data().
+ */
+ sec->base->data->d_buf = dst;
+ sec->base->data->d_size = dst_offset;
+ }
+}
+
static int is_null_sym(struct symbol *sym)
{
return !strlen(sym->name);
@@ -2190,6 +2315,8 @@ int main(int argc, char *argv[])
log_debug("Process special sections\n");
kpatch_process_special_sections(kelf_patched);
+ log_debug("Strip undefined elements of known size\n");
+ livepatch_strip_undefined_elements(kelf_patched);
log_debug("Verify patchability\n");
kpatch_verify_patchability(kelf_patched);