create-diff-object: fix relocations used for ZERO_PAGE(0)

On x86_64, GCC generates the following instruction to compute
'empty_zero_page - __START_KERNEL_map' (__phys_addr_nodebug(), used in
the implementation of ZERO_PAGE()):

    48 ba 00 00 00 00 00 00 00 00   movabs $0x0,%rdx
          R_X86_64_64  empty_zero_page+0x80000000

__START_KERNEL_map is 0xffffffff80000000.

However, the relocation addend becomes wrong in the patch module:

    48 ba 00 00 00 00 00 00 00 00   movabs $0x0,%rdx
          R_X86_64_64  empty_zero_page-0x80000000

Note the sign of the addend.

As a result, ZERO_PAGE(0) returns a wrong value in any function touched
by the patch, which may lead to memory corruption and difficult-to-debug
kernel crashes.

The cause is that 'struct rela' uses 'int' for the addend, which is not
enough to store such values. r_addend from Elf64_Rela is int64_t
(Elf64_Sxword) for that.

Let us use 'long' instead of 'int' for the addend in 'struct rela'.

v2:
* Moved 'addend' field after 'offset' in struct rela to facilitate
  structure packing (suggested by Kamalesh Babulal).

Fixes #1064.

Signed-off-by: Evgenii Shatokhin <eshatokhin@virtuozzo.com>

kpatch-build/create-diff-object.c

@@ -374,14 +374,14 @@ static int rela_equal(struct rela *rela1, struct rela *rela2)
 		 */
 		memcpy(&toc_data1, rela1->sym->sec->data->d_buf + rela1->addend, sizeof(toc_data1));
 		if (!toc_data1)
-			ERROR(".toc entry not found %s + %x", rela1->sym->name, rela1->addend);
+			ERROR(".toc entry not found %s + %lx", rela1->sym->name, rela1->addend);
 	}
 
 	rela_toc2 = toc_rela(rela2);
 	if (!rela_toc2) {
 		memcpy(&toc_data2, rela2->sym->sec->data->d_buf + rela2->addend, sizeof(toc_data2));
 		if (!toc_data2)
-			ERROR(".toc entry not found %s + %x", rela2->sym->name, rela2->addend);
+			ERROR(".toc entry not found %s + %lx", rela2->sym->name, rela2->addend);
 	}
 
 	if (!rela_toc1 && !rela_toc2)
@@ -1369,7 +1369,7 @@ static void kpatch_replace_sections_syms(struct kpatch_elf *kelf)
 					   rela->addend + add_off >= end)
 					continue;
 
-				log_debug("%s: replacing %s+%d reference with %s+%d\n",
+				log_debug("%s: replacing %s+%ld reference with %s+%ld\n",
 					  sec->name,
 					  rela->sym->name, rela->addend,
 					  sym->name, rela->addend - start);
@@ -2070,7 +2070,7 @@ static void kpatch_regenerate_special_section(struct kpatch_elf *kelf,
 			if (is_dynamic_debug_symbol(key->sym))
 				continue;
 
-			ERROR("Found a jump label at %s()+0x%x, using key %s.  Jump labels aren't currently supported.  Use static_key_enabled() instead.",
+			ERROR("Found a jump label at %s()+0x%lx, using key %s.  Jump labels aren't currently supported.  Use static_key_enabled() instead.",
 			      code->sym->name, code->addend, key->sym->name);
 
 			continue;
@@ -2237,8 +2237,8 @@ static void kpatch_check_relocations(struct kpatch_elf *kelf)
 		list_for_each_entry(rela, &sec->relas, list) {
 			if (rela->sym->sec) {
 				sdata = rela->sym->sec->data;
-				if (rela->addend > (int)sdata->d_size) {
-					ERROR("out-of-range relocation %s+%x in %s", rela->sym->sec->name,
+				if (rela->addend > (long)sdata->d_size) {
+					ERROR("out-of-range relocation %s+%lx in %s", rela->sym->sec->name,
 							rela->addend, sec->name);
 				}
 			}

kpatch-build/kpatch-elf.c

@@ -194,15 +194,15 @@ void kpatch_create_rela_list(struct kpatch_elf *kelf, struct section *sec)
 		    (rela->sym->sec->sh.sh_flags & SHF_STRINGS)) {
 			rela->string = rela->sym->sec->data->d_buf + rela->addend;
 			if (!rela->string)
-				ERROR("could not lookup rela string for %s+%d",
+				ERROR("could not lookup rela string for %s+%ld",
 				      rela->sym->name, rela->addend);
 		}
 
 		if (skip)
 			continue;
-		log_debug("offset %d, type %d, %s %s %d", rela->offset,
+		log_debug("offset %d, type %d, %s %s %ld", rela->offset,
 			rela->type, rela->sym->name,
-			(rela->addend < 0)?"-":"+", abs(rela->addend));
+			(rela->addend < 0)?"-":"+", labs(rela->addend));
 		if (rela->string)
 			log_debug(" (string = %s)", rela->string);
 		log_debug("\n");
@@ -403,11 +403,11 @@ void kpatch_dump_kelf(struct kpatch_elf *kelf)
 				goto next;
 			printf("rela section expansion\n");
 			list_for_each_entry(rela, &sec->relas, list) {
-				printf("sym %d, offset %d, type %d, %s %s %d\n",
+				printf("sym %d, offset %d, type %d, %s %s %ld\n",
 				       rela->sym->index, rela->offset,
 				       rela->type, rela->sym->name,
 				       (rela->addend < 0)?"-":"+",
-				       abs(rela->addend));
+				       labs(rela->addend));
 			}
 		} else {
 			if (sec->sym)

kpatch-build/kpatch-elf.h

@@ -90,8 +90,8 @@ struct rela {
 	GElf_Rela rela;
 	struct symbol *sym;
 	unsigned int type;
-	int addend;
 	unsigned int offset;
+	long addend;
 	char *string;
 	bool need_dynrela;
 };