x86-64 memrchr: 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 memrchr 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/memrchr.S: Use RDX_LP for length.
	* sysdeps/x86_64/multiarch/memrchr-avx2.S: Likewise.
	* sysdeps/x86_64/x32/Makefile (tests): Add tst-size_t-memrchr.
	* sysdeps/x86_64/x32/tst-size_t-memrchr.c: New file.

2 files changed, 59 insertions, 1 deletions

diff --git a/sysdeps/x86_64/x32/Makefile b/sysdeps/x86_64/x32/Makefile
index 2fe1e5ac5a..e99dbd7c86 100644
--- a/sysdeps/x86_64/x32/Makefile
+++ b/sysdeps/x86_64/x32/Makefile
@@ -6,7 +6,8 @@ CFLAGS-s_llround.c += -fno-builtin-lround
 endif
 
 ifeq ($(subdir),string)
-tests += tst-size_t-memchr tst-size_t-memcmp tst-size_t-memcpy
+tests += tst-size_t-memchr tst-size_t-memcmp tst-size_t-memcpy \
+	 tst-size_t-memrchr
 endif
 
 ifeq ($(subdir),wcsmbs)
diff --git a/sysdeps/x86_64/x32/tst-size_t-memrchr.c b/sysdeps/x86_64/x32/tst-size_t-memrchr.c
new file mode 100644
index 0000000000..c83699c097
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-memrchr.c
@@ -0,0 +1,57 @@
+/* Test memrchr 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/>.  */
+
+#define TEST_NAME "memrchr"
+#include "test-size_t.h"
+
+IMPL (memchr, 1)
+
+typedef void * (*proto_t) (const void *, int, size_t);
+
+static void *
+__attribute__ ((noinline, noclone))
+do_memrchr (parameter_t a, parameter_t b)
+{
+  return CALL (&b, a.p, (uintptr_t) b.p, a.len);
+}
+
+static int
+test_main (void)
+{
+  test_init ();
+
+  parameter_t src = { { page_size }, buf2 };
+  parameter_t c = { { 0 }, (void *) (uintptr_t) 0x12 };
+
+  int ret = 0;
+  FOR_EACH_IMPL (impl, 0)
+    {
+      c.fn = impl->fn;
+      void * res = do_memrchr (src, c);
+      if (res)
+	{
+	  error (0, 0, "Wrong result in function %s: %p != NULL",
+		 impl->name, res);
+	  ret = 1;
+	}
+    }
+
+  return ret ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
+#include <support/test-driver.c>