x86-64 strncpy: 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 strncpy 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/strcpy-avx2.S: Use RDX_LP for length.
	* sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S: Likewise.
	* sysdeps/x86_64/multiarch/strcpy-ssse3.S: Likewise.
	* sysdeps/x86_64/x32/Makefile (tests): Add tst-size_t-strncpy.
	* sysdeps/x86_64/x32/tst-size_t-strncpy.c: New file.

5 files changed, 66 insertions, 8 deletions

diff --git a/sysdeps/x86_64/multiarch/strcpy-avx2.S b/sysdeps/x86_64/multiarch/strcpy-avx2.S
index 81677f9060..e72a0cad7d 100644
--- a/sysdeps/x86_64/multiarch/strcpy-avx2.S
+++ b/sysdeps/x86_64/multiarch/strcpy-avx2.S
@@ -49,8 +49,8 @@
 	.section .text.avx,"ax",@progbits
 ENTRY (STRCPY)
 #  ifdef USE_AS_STRNCPY
-	mov	%rdx, %r8
-	test	%r8, %r8
+	mov	%RDX_LP, %R8_LP
+	test	%R8_LP, %R8_LP
 	jz	L(ExitZero)
 #  endif
 	mov	%rsi, %rcx
diff --git a/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S b/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S
index b7c79976ea..0d6914e113 100644
--- a/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S
+++ b/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S
@@ -40,8 +40,8 @@
 .text
 ENTRY (STRCPY)
 #  ifdef USE_AS_STRNCPY
-	mov	%rdx, %r8
-	test	%r8, %r8
+	mov	%RDX_LP, %R8_LP
+	test	%R8_LP, %R8_LP
 	jz	L(ExitZero)
 #  endif
 	mov	%rsi, %rcx
diff --git a/sysdeps/x86_64/multiarch/strcpy-ssse3.S b/sysdeps/x86_64/multiarch/strcpy-ssse3.S
index ec53f2a632..39e6ad762c 100644
--- a/sysdeps/x86_64/multiarch/strcpy-ssse3.S
+++ b/sysdeps/x86_64/multiarch/strcpy-ssse3.S
@@ -31,13 +31,13 @@ ENTRY (STRCPY)
 
 	mov	%rsi, %rcx
 #  ifdef USE_AS_STRNCPY
-	mov	%rdx, %r8
+	mov	%RDX_LP, %R8_LP
 #  endif
 	mov	%rdi, %rdx
 #  ifdef USE_AS_STRNCPY
-	test	%r8, %r8
+	test	%R8_LP, %R8_LP
 	jz	L(Exit0)
-	cmp	$8, %r8
+	cmp	$8, %R8_LP
 	jbe	L(StrncpyExit8Bytes)
 # endif
 	cmpb	$0, (%rcx)
diff --git a/sysdeps/x86_64/x32/Makefile b/sysdeps/x86_64/x32/Makefile
index db30283977..2a9e20a90b 100644
--- a/sysdeps/x86_64/x32/Makefile
+++ b/sysdeps/x86_64/x32/Makefile
@@ -8,7 +8,7 @@ endif
 ifeq ($(subdir),string)
 tests += tst-size_t-memchr tst-size_t-memcmp tst-size_t-memcpy \
 	 tst-size_t-memrchr tst-size_t-memset tst-size_t-strncasecmp \
-	 tst-size_t-strncmp
+	 tst-size_t-strncmp tst-size_t-strncpy
 endif
 
 ifeq ($(subdir),wcsmbs)
diff --git a/sysdeps/x86_64/x32/tst-size_t-strncpy.c b/sysdeps/x86_64/x32/tst-size_t-strncpy.c
new file mode 100644
index 0000000000..4dec71e6b3
--- /dev/null
+++ b/sysdeps/x86_64/x32/tst-size_t-strncpy.c
@@ -0,0 +1,58 @@
+/* Test strncpy 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 "strncpy"
+#include "test-size_t.h"
+
+IMPL (strncpy, 1)
+
+typedef char *(*proto_t) (char *, const char*, size_t);
+
+static void *
+__attribute__ ((noinline, noclone))
+do_strncpy (parameter_t a, parameter_t b)
+{
+  return CALL (&b, a.p, b.p, a.len);
+}
+
+static int
+test_main (void)
+{
+  test_init ();
+
+  parameter_t dest = { { page_size }, buf1 };
+  parameter_t src = { { 0 }, buf2 };
+
+  int ret = 0;
+  FOR_EACH_IMPL (impl, 0)
+    {
+      src.fn = impl->fn;
+      do_strncpy (dest, src);
+      int res = strncmp (dest.p, src.p, dest.len);
+      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>