[Xen-devel] [livepatch-build-tools part3 2/3] create-diff-object: Extend patchability verification: STN_UNDEF

[Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>]

During verification check if all sections do not contain any entries
with undefined symbols (STN_UNDEF). This situation can happen when a
section is copied over from its original object to a patched object,
but various symbols related to the section are not copied along.
This scenario happens typically during stacked hotpatches creation
(between 2 different hotpatch modules).

Signed-off-by: Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>
Reviewed-by: Martin Pohlack <mpohlack@xxxxxxxxx>
Reviewed-by: Bjoern Doebel <doebel@xxxxxxxxx>
Reviewed-by: Norbert Manthey <nmanthey@xxxxxxxxx>
Reviewed-by: Andra-Irina Paraschiv <andraprs@xxxxxxxxxx>

CR: https://code.amazon.com/reviews/CR-7368645
---
 create-diff-object.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/create-diff-object.c b/create-diff-object.c
index af2245c..96b6716 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -1448,6 +1448,31 @@ static void kpatch_print_changes(struct kpatch_elf *kelf)
        }
 }
 
+static inline int get_section_entry_size(const struct section *sec, struct 
kpatch_elf *kelf)
+{
+       int entry_size;
+
+       /*
+        * Base sections typically do not define fixed size elements.
+        * Detect section's element size in case it's a special section.
+        * Otherwise, skip it due to an unknown sh_entsize.
+        */
+       entry_size = sec->sh.sh_entsize;
+       if (entry_size == 0) {
+               struct special_section *special;
+
+               /* Find special section group_size. */
+               for (special = special_sections; special->name; special++) {
+                       /* Match sections starting with special->name prefix */
+                       if (!strncmp(sec->name, special->name, 
strlen(special->name))) {
+                               return special->group_size(kelf, 0);
+                       }
+               }
+        }
+
+        return entry_size;
+}
+
 static void kpatch_verify_patchability(struct kpatch_elf *kelf)
 {
        struct section *sec;
@@ -1471,6 +1496,41 @@ static void kpatch_verify_patchability(struct kpatch_elf 
*kelf)
                        errs++;
                }
 
+               if (sec->include) {
+                       if (!is_standard_section(sec) && !is_rela_section(sec) 
&&
+                           !is_debug_section(sec) && !is_special_section(sec)) 
{
+                               if (!is_referenced_section(sec, kelf)) {
+                                       log_normal("section %s included, but 
not referenced\n", sec->name);
+                                       errs++;
+                               }
+                       }
+
+                       /* Check if a RELA section does not contain any entries 
with
+                        * undefined symbols (STN_UNDEF). This situation can 
happen
+                        * when a section is copied over from its original 
object to
+                        * a patched object, but various symbols related to the 
section
+                        * are not copied along.
+                        */
+                       if (is_rela_section(sec)) {
+                               int offset, entry_size = 
get_section_entry_size(sec, kelf);
+                               struct rela *rela;
+
+                               for ( offset = 0; offset < 
sec->base->data->d_size && entry_size; offset += entry_size ) {
+                                       list_for_each_entry(rela, &sec->relas, 
list) {
+                                               if (rela->offset < offset || 
rela->offset >= offset + entry_size)
+                                                       continue;
+
+                                               if 
((GELF_R_SYM(rela->rela.r_info) == STN_UNDEF) ||
+                                                   (!rela->sym->include && 
(rela->sym->status == SAME))) {
+                                                       log_normal("section %s 
has an entry with a STN_UNDEF symbol: %s\n",
+                                                                  sec->name, 
rela->sym->name ? rela->sym->name : "none");
+                                                       errs++;
+                                               }
+                                       }
+                               }
+                       }
+               }
+
                /*
                 * ensure we aren't including .data.* or .bss.*
                 * (.data.unlikely is ok b/c it only has __warned vars)
-- 
2.16.5




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Krausenstr. 38
10117 Berlin
Geschaeftsfuehrer: Christian Schlaeger, Ralf Herbrich
Ust-ID: DE 289 237 879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B



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