commit 08beb3a3f4f46e306fffe184a08c5664bf0e13d6

Author: Noah Goldstein <goldstein.w.n@gmail.com>

Date:   Sun Jan 9 16:02:28 2022 -0600

    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 459eeed09f5e276e..d5aa6daa46c7ed25 100644

--- 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