elf/rtld: Fix auxiliary vector for enable_secure

Starting with commit
59974938fe
elf/rtld: Count skipped environment variables for enable_secure

The new testcase elf/tst-tunables-enable_secure-env segfaults on s390 (31bit).
There _start parses the auxiliary vector for some additional checks.

Therefore it skips over the zeros after the environment variables ...
0x7fffac20:     0x7fffbd17      0x7fffbd32      0x7fffbd69      0x00000000
------------------------------------------------^^^last environment variable

... and then it parses the auxiliary vector and stops at AT_NULL.
0x7fffac30:     0x00000000      0x00000021      0x00000000      0x00000000
--------------------------------^^^AT_SYSINFO_EHDR--------------^^^AT_NULL
----------------^^^newp-----------------------------------------^^^oldp
Afterwards it tries to access AT_PHDR which points to somewhere and segfaults.

Due to not incorporating the skip_env variable in the computation of oldp
when shuffling down the auxv in rtld.c, it just copies one entry with AT_NULL
and value 0x00000021 and stops the loop.  In reality we have skipped
GLIBC_TUNABLES environment variable (=> skip_env=1). Thus we should copy from
here:
0x7fffac40:     0x00000021      0x7ffff000      0x00000010      0x007fffff
----------------^^^fixed-oldp

This patch fixes the computation of oldp when shuffling down auxiliary vector.
It also adds some checks in the testcase.  Those checks also fail on
s390x (64bit) and x86_64 without the fix.

Co-authored-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

elf/Makefile

@@ -1224,7 +1224,6 @@ tests-special += \
   $(objpfx)tst-trace3.out \
   $(objpfx)tst-trace4.out \
   $(objpfx)tst-trace5.out \
-  $(objpfx)tst-tunables-enable_secure-env.out \
   $(objpfx)tst-unused-dep-cmp.out \
   $(objpfx)tst-unused-dep.out \
   # tests-special
@@ -2252,13 +2251,7 @@ $(objpfx)tst-unused-dep-cmp.out: $(objpfx)tst-unused-dep.out
 	cmp $< /dev/null > $@; \
 	$(evaluate-test)
 
-$(objpfx)tst-tunables-enable_secure-env.out: $(objpfx)tst-tunables-enable_secure-env
-	$(test-wrapper-env) \
-	GLIBC_TUNABLES=glibc.rtld.enable_secure=1 \
-	$(rtld-prefix) \
-	  $< > $@; \
-	$(evaluate-test)
-
+tst-tunables-enable_secure-env-ARGS = -- $(host-test-program-cmd)
 
 $(objpfx)tst-audit11.out: $(objpfx)tst-auditmod11.so $(objpfx)tst-audit11mod1.so
 tst-audit11-ENV = LD_AUDIT=$(objpfx)tst-auditmod11.so

elf/rtld.c

@@ -1327,7 +1327,7 @@ _dl_start_args_adjust (int skip_args, int skip_env)
 
   /* Shuffle auxv down. */
   ElfW(auxv_t) ax;
-  char *oldp = (char *) (p + 1);
+  char *oldp = (char *) (p + 1 + skip_env);
   char *newp = (char *) (sp + 1);
   do
     {

elf/tst-tunables-enable_secure-env.c

@@ -17,15 +17,136 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#include <array_length.h>
+#include <errno.h>
+#include <getopt.h>
+#include <intprops.h>
+#include <stdlib.h>
 #include <support/capture_subprocess.h>
 #include <support/check.h>
+#ifdef __linux__
+# define HAVE_AUXV 1
+# include <sys/auxv.h>
+#else
+# define HAVE_AUXV 0
+#endif
+
+/* Nonzero if the program gets called via `exec'.  */
+#define CMDLINE_OPTIONS \
+  { "restart", no_argument, &restart, 1 },
+static int restart;
+
+/* Hold the four initial argument used to respawn the process, plus the extra
+   '--direct', '--restart', auxiliary vector values, and final NULL.  */
+static char *spargs[11];
+
+#if HAVE_AUXV
+static void
+check_auxv (unsigned long type, char *argv)
+{
+  char *endptr;
+  errno = 0;
+  unsigned long int varg = strtol (argv, &endptr, 10);
+  TEST_VERIFY_EXIT (errno == 0);
+  TEST_VERIFY_EXIT (*endptr == '\0');
+  errno = 0;
+  unsigned long int v = getauxval (type);
+  TEST_COMPARE (errno, 0);
+  TEST_COMPARE (varg, v);
+}
+#endif
+
+/* Called on process re-execution.  */
+_Noreturn static void
+handle_restart (int argc, char *argv[])
+{
+  TEST_VERIFY (getenv ("GLIBC_TUNABLES") == NULL);
+  TEST_VERIFY (getenv ("LD_BIND_NOW") == NULL);
+
+#if HAVE_AUXV
+  TEST_VERIFY_EXIT (argc == 4);
+  check_auxv (AT_PHENT, argv[0]);
+  check_auxv (AT_PHNUM, argv[1]);
+  check_auxv (AT_PAGESZ, argv[2]);
+  check_auxv (AT_HWCAP, argv[3]);
+#endif
+
+  exit (EXIT_SUCCESS);
+}
 
 static int
 do_test (int argc, char *argv[])
 {
-  /* Ensure that no assertions are hit when a dynamically linked application
-     runs.  This test requires that GLIBC_TUNABLES=glibc.rtld.enable_secure=1
-     is set. */
+  /* We must have either:
+
+     - four parameter if called initially:
+       + path for ld.so            [optional]
+       + "--library-path"          [optional]
+       + the library path          [optional]
+       + the application name
+
+     - either parameters left if called through re-execution.
+       + auxiliary vector value 1
+       + auxiliary vector value 2
+       + auxiliary vector value 3
+       + auxiliary vector value 4
+  */
+  if (restart)
+    handle_restart (argc - 1, &argv[1]);
+
+  TEST_VERIFY_EXIT (argc == 2 || argc == 5);
+
+#if HAVE_AUXV
+  struct
+  {
+    unsigned long int type;
+    char str[INT_BUFSIZE_BOUND (unsigned long)];
+  } auxvals[] =
+  {
+    /* Check some auxiliary values that should be constant over process
+       re-execution.  */
+    { AT_PHENT },
+    { AT_PHNUM },
+    { AT_PAGESZ },
+    { AT_HWCAP },
+  };
+  for (int i = 0; i < array_length (auxvals); i++)
+  {
+    unsigned long int v = getauxval (auxvals[i].type);
+    snprintf (auxvals[i].str, sizeof auxvals[i].str, "%lu", v);
+  }
+#endif
+
+  {
+    int i;
+    for (i = 0; i < argc - 1; i++)
+      spargs[i] = argv[i + 1];
+    spargs[i++] = (char *) "--direct";
+    spargs[i++] = (char *) "--restart";
+#if HAVE_AUXV
+    for (int j = 0; j < array_length (auxvals); j++)
+      spargs[i++] = auxvals[j].str;
+#endif
+    spargs[i] = NULL;
+  }
+
+  {
+    char *envs[] =
+    {
+      /* Add some environment variable that should be filtered out.  */
+      (char *) "GLIBC_TUNABLES=glibc.rtld.enable_secure=1",
+      (char* ) "LD_BIND_NOW=0",
+      NULL,
+    };
+    struct support_capture_subprocess result
+      = support_capture_subprogram (spargs[0], spargs, envs);
+    support_capture_subprocess_check (&result,
+				      "tst-tunables-enable_secure-env",
+				      0,
+				      sc_allow_none);
+    support_capture_subprocess_free (&result);
+  }
+
   return 0;
 }