elf/tst-big-note: Improve accuracy of test [BZ #20419]

It is possible that the link editor injects an allocated ABI tag note
before the artificial, allocated large note in the test.  Note parsing
in open_verify stops when the first ABI tag note is encountered, so if
the ABI tag note comes first, the problematic code is not actually
exercised.

Also tweak the artificial note so that it is a syntactically valid
4-byte aligned note, in case the link editor tries to parse notes and
process them.

Improves the testing part of commit 0065aaaaae51cd60210ec3a7e13.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

diff --git a/ChangeLog b/ChangeLog
index 85506ef..1ca155e 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2019-03-01  Florian Weimer  <fweimer@redhat.com>
+
+       [BZ #20419]
+       * elf/tst-big-note-lib.S: Create a syntactically valid note.
+       * elf/Makefile (tst-big-note-lib.so): Do not link with startup
+       code, to avoid creating an ABI tag note.
+       (modules-names-nobuild): Add tst-big-note-lib.
+
 2019-03-01  Stefan Liebler  <stli@linux.ibm.com>
 
        * sysdeps/s390/wcscpy-vx.S: Add strong aliases to

diff --git a/elf/Makefile b/elf/Makefile
index 5520407..310a37c 100644 (file)
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -316,8 +316,8 @@ endif
 modules-execstack-yes = tst-execstack-mod
 extra-test-objs += $(addsuffix .os,$(strip $(modules-names)))
 
-# filtmod1.so has a special rule
-modules-names-nobuild := filtmod1
+# filtmod1.so, tst-big-note-lib.so have special rules.
+modules-names-nobuild := filtmod1 tst-big-note-lib
 
 tests += $(tests-static)
 
@@ -1515,6 +1515,11 @@ tst-libc_dlvsym-static-ENV = \
 $(objpfx)tst-libc_dlvsym-static.out: $(objpfx)tst-libc_dlvsym-dso.so
 
 $(objpfx)tst-big-note: $(objpfx)tst-big-note-lib.so
+# Avoid creating an ABI tag note, which may come before the
+# artificial, large note in tst-big-note-lib.o and invalidate the
+# test.
+$(objpfx)tst-big-note-lib.so: $(objpfx)tst-big-note-lib.o
+       $(LINK.o) -shared -o $@ $(LDFLAGS.so) $<
 
 $(objpfx)tst-unwind-ctor: $(objpfx)tst-unwind-ctor-lib.so
 

diff --git a/elf/tst-big-note-lib.S b/elf/tst-big-note-lib.S
index e2008cf..721686f 100644 (file)
--- a/elf/tst-big-note-lib.S
+++ b/elf/tst-big-note-lib.S
@@ -20,7 +20,13 @@
    On a typical Linux system with 8MiB "ulimit -s", that was enough
    to trigger stack overflow in open_verify.  */
 
+#define NOTE_SIZE 8*1024*1024
+
 .pushsection .note.big,"a"
-.balign 4
-.fill 8*1024*1024, 1, 0
+       .balign 4
+       .long 5                 /* n_namesz.  Length of "GLIBC".  */
+       .long NOTE_SIZE         /* n_descsz.  */
+       .long 0                 /* n_type.  */
+       .ascii "GLIBC\0\0\0"    /* Name and alignment to four bytes.  */
+       .fill NOTE_SIZE, 1, 0
 .popsection