x86: Fix __wcsncmp_evex in strcmp-evex.S [BZ# 28755]

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>
(cherry picked from commit 7e08db3359c86c94918feb33a1182cd0ff3bb10b)

diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
index 459eeed09f5e276e6e28694d5b2af85188da473d..d5aa6daa46c7ed25e22d14fc3e272ca5a6718f60 100644 (file)
--- a/sysdeps/x86_64/multiarch/strcmp-evex.S
+++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
@@ -97,6 +97,16 @@ 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