diff --git a/NEWS b/NEWS
index cc20102fda..2885c42aa5 100644
--- a/NEWS
+++ b/NEWS
@@ -101,6 +101,12 @@ Security related changes:
   denial of service due to resource exhaustion when processing getaddrinfo
   calls with crafted host names.  Reported by Guido Vranken.
 
+  CVE-2019-6488: 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.  When
+  it happens, the string/memory functions written in assembly will cause
+  buffer overflow if the full 64-bit register is used as the 32-bit
+  size_t value.  Reported by Florian Weimer.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/sysdeps/x86_64/memchr.S b/sysdeps/x86_64/memchr.S
index a6f3ebba22..ec96365217 100644
--- a/sysdeps/x86_64/memchr.S
+++ b/sysdeps/x86_64/memchr.S
@@ -34,12 +34,16 @@ ENTRY(MEMCHR)
 	mov	%edi, %ecx
 
 #ifdef USE_AS_WMEMCHR
-	test	%rdx, %rdx
+	test	%RDX_LP, %RDX_LP
 	jz	L(return_null)
-	shl	$2, %rdx
+	shl	$2, %RDX_LP
 #else
+# ifdef __ILP32__
+	/* Clear the upper 32 bits.  */
+	movl	%edx, %edx
+# endif
 	punpcklbw %xmm1, %xmm1
-	test	%rdx, %rdx
+	test	%RDX_LP, %RDX_LP
 	jz	L(return_null)
 	punpcklbw %xmm1, %xmm1
 #endif
diff --git a/sysdeps/x86_64/multiarch/memchr-avx2.S b/sysdeps/x86_64/multiarch/memchr-avx2.S
index 9f98b7ec60..cfec1657b6 100644
--- a/sysdeps/x86_64/multiarch/memchr-avx2.S
+++ b/sysdeps/x86_64/multiarch/memchr-avx2.S
@@ -40,16 +40,20 @@
 ENTRY (MEMCHR)
 # ifndef USE_AS_RAWMEMCHR
 	/* Check for zero length.  */
-	testq	%rdx, %rdx
+	test	%RDX_LP, %RDX_LP
 	jz	L(null)
 # endif
 	movl	%edi, %ecx
 	/* Broadcast CHAR to YMM0.  */
 	vmovd	%esi, %xmm0
 # ifdef USE_AS_WMEMCHR
-	shl	$2, %rdx
+	shl	$2, %RDX_LP
 	vpbroadcastd %xmm0, %ymm0
 # else
+#  ifdef __ILP32__
+	/* Clear the upper 32 bits.  */
+	movl	%edx, %edx
+#  endif
 	vpbroadcastb %xmm0, %ymm0
 # endif
 	/* Check if we may cross page boundary with one vector load.  */
diff --git a/sysdeps/x86_64/x32/Makefile b/sysdeps/x86_64/x32/Makefile
index f2ebc24fb0..7d528889c6 100644
--- a/sysdeps/x86_64/x32/Makefile
+++ b/sysdeps/x86_64/x32/Makefile
@@ -4,3 +4,11 @@ ifeq ($(subdir),math)
 # 64-bit llround.  Add -fno-builtin-lround to silence the compiler.
 CFLAGS-s_llround.c += -fno-builtin-lround
 endif
+
+ifeq ($(subdir),string)
+tests += tst-size_t-memchr
+endif
+
+ifeq ($(subdir),wcsmbs)
+tests += tst-size_t-wmemchr
+endif
diff --git a/sysdeps/x86_64/x32/test-size_t.h b/sysdeps/x86_64/x32/test-size_t.h
new file mode 100644
index 0000000000..78a940863e
--- /dev/null
+++ b/sysdeps/x86_64/x32/test-size_t.h
@@ -0,0 +1,35 @@
+/* Test string/memory functions 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_MAIN
+#include <string/test-string.h>
+
+/* On x32, parameter_t may be passed in a 64-bit register with the LEN
+   field in the lower 32 bits.  When the LEN field of 64-bit register
+   is passed to string/memory function as the size_t parameter, only
+   the lower 32 bits can be used.  */
+typedef struct
+{
+  union
+    {
+      size_t len;
+      void (*fn) (void);
+    };
+  void *p;
+} parameter_t;
diff --git a/sysdeps/x86_64/x32/tst-size_t-memchr.c b/sysdeps/x86_64/x32/tst-size_t-memchr.c
new file mode 100644
index 0000000000..29a3daf102
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-memchr.c
@@ -0,0 +1,72 @@
+/* Test memchr 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/>.  */
+
+#ifndef WIDE
+# define TEST_NAME "memchr"
+#else
+# define TEST_NAME "wmemchr"
+#endif /* WIDE */
+#include "test-size_t.h"
+
+#ifndef WIDE
+# define MEMCHR memchr
+# define CHAR char
+# define UCHAR unsigned char
+#else
+# include <wchar.h>
+# define MEMCHR wmemchr
+# define CHAR wchar_t
+# define UCHAR wchar_t
+#endif /* WIDE */
+
+IMPL (MEMCHR, 1)
+
+typedef CHAR * (*proto_t) (const CHAR*, int, size_t);
+
+static CHAR *
+__attribute__ ((noinline, noclone))
+do_memchr (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 / sizeof (CHAR) }, buf2 };
+  parameter_t c = { { 0 }, (void *) (uintptr_t) 0x12 };
+
+  int ret = 0;
+  FOR_EACH_IMPL (impl, 0)
+    {
+      c.fn = impl->fn;
+      CHAR *res = do_memchr (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>
diff --git a/sysdeps/x86_64/x32/tst-size_t-wmemchr.c b/sysdeps/x86_64/x32/tst-size_t-wmemchr.c
new file mode 100644
index 0000000000..877801d646
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-wmemchr.c
@@ -0,0 +1,20 @@
+/* Test wmemchr 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 WIDE 1
+#include "tst-size_t-memchr.c"
