x86-64 strncmp family: Properly handle the length parameter [BZ# 24097]

On x32, the size_t parameter may be passed in the lower 32 bits of a
64-bit register with the non-zero upper 32 bits.  The string/memory
functions written in assembly can only use the lower 32 bits of a
64-bit register as length or must clear the upper 32 bits before using
the full 64-bit register for length.

This pach fixes the strncmp family for x32.  Tested on x86-64 and x32.
On x86-64, libc.so is the same with and withou the fix.

	[BZ# 24097]
	CVE-2019-6488
	* sysdeps/x86_64/multiarch/strcmp-avx2.S: Use RDX_LP for length.
	* sysdeps/x86_64/multiarch/strcmp-sse42.S: Likewise.
	* sysdeps/x86_64/strcmp.S: Likewise.
	* sysdeps/x86_64/x32/Makefile (tests): Add tst-size_t-strncasecmp,
	tst-size_t-strncmp and tst-size_t-wcsncmp.
	* sysdeps/x86_64/x32/tst-size_t-strncasecmp.c: New file.
	* sysdeps/x86_64/x32/tst-size_t-strncmp.c: Likewise.
	* sysdeps/x86_64/x32/tst-size_t-wcsncmp.c: Likewise.

1 files changed, 78 insertions, 0 deletions

diff --git a/sysdeps/x86_64/x32/tst-size_t-strncmp.c b/sysdeps/x86_64/x32/tst-size_t-strncmp.c
new file mode 100644
index 0000000000..54e6bd83ef
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-strncmp.c
@@ -0,0 +1,78 @@
+/* Test strncmp with size_t in the lower 32 bits of 64-bit register.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifdef WIDE
+# define TEST_NAME "wcsncmp"
+#else
+# define TEST_NAME "strncmp"
+#endif
+
+#include "test-size_t.h"
+
+#ifdef WIDE
+# include <wchar.h>
+
+# define STRNCMP wcsncmp
+# define STRNCPY wcsncpy
+# define CHAR wchar_t
+#else
+# define STRNCMP strncmp
+# define STRNCPY strncpy
+# define CHAR char
+#endif
+
+IMPL (STRNCMP, 1)
+
+typedef int (*proto_t) (const CHAR *, const CHAR *, size_t);
+
+
+static int
+__attribute__ ((noinline, noclone))
+do_strncmp (parameter_t a, parameter_t b)
+{
+  return CALL (&b, a.p, b.p, a.len);
+}
+
+static int
+test_main (void)
+{
+  test_init ();
+
+  size_t size = page_size / sizeof (CHAR);
+  parameter_t dest = { { size }, buf1 };
+  parameter_t src = { { 0 }, buf2 };
+
+  STRNCPY ((CHAR *) buf1, (const CHAR *) buf2, size);
+
+  int ret = 0;
+  FOR_EACH_IMPL (impl, 0)
+    {
+      src.fn = impl->fn;
+      int res = do_strncmp (dest, src);
+      if (res)
+	{
+	  error (0, 0, "Wrong result in function %s: %i != 0",
+		 impl->name, res);
+	  ret = 1;
+	}
+    }
+
+  return ret ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
+#include <support/test-driver.c>