elf/tst-big-note: Improve accuracy of test [BZ #20419]
Commit Message
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.
Tested on ppc64le, including that the test now crashes as expected on a
glibc-2.17-derived glibc without the backport of the original fix.
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.
Comments
On Fri, Mar 1, 2019 at 6:28 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> It is possible that the link editor injects an allocated ABI tag note
> before the artificial, allocated large note in the test.
Looks good to me. Thanks!
> +$(objpfx)tst-big-note-lib.so: $(objpfx)tst-big-note-lib.o
> + $(LINK.o) -shared -o $@ $(LDFLAGS.so) $<
I got lost tracing through Makefile machinery trying to find how
-nostartfiles gets into the link line here, but I'll take your word
for it :-)
@@ -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
@@ -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