[PATCH v3 2/7] x86: Fix __wcsncmp_evex in strcmp-evex.S [BZ# 28755]

[Noah Goldstein]

Fixes [BZ# 28755] for wcsncmp by redirecting length >= 2^56 to
__wcscmp_evex. For x86_64 this covers the entire address range so any
length larger could not possibly be used to bound `s1` or `s2`.

test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass.

Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
 sysdeps/x86_64/multiarch/strcmp-evex.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
index 1d971f3889..0cd939d5af 100644
--- a/sysdeps/x86_64/multiarch/strcmp-evex.S
+++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
@@ -104,6 +104,16 @@ ENTRY (STRCMP)
 	je	L(char0)
 	jb	L(zero)
 #  ifdef USE_AS_WCSCMP
+#  ifndef __ILP32__
+	movq	%rdx, %rcx
+	/* Check if length could overflow when multiplied by
+	   sizeof(wchar_t). Checking top 8 bits will cover all potential
+	   overflow cases as well as redirect cases where its impossible to
+	   length to bound a valid memory region. In these cases just use
+	   'wcscmp'.  */
+	shrq	$56, %rcx
+	jnz	__wcscmp_evex
+#  endif
 	/* Convert units: from wide to byte char.  */
 	shl	$2, %RDX_LP
 #  endif
-- 
2.25.1