commit e3255e7d2188d1731aad83ad0dc147513560aa1e

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

Date:   Tue Sep 20 17:58:04 2022 -0700

    x86: Fix wcsnlen-avx2 page cross length comparison [BZ #29591]

    Previous implementation was adjusting length (rsi) to match

    bytes (eax), but since there is no bound to length this can cause

    overflow.

    Fix is to just convert the byte-count (eax) to length by dividing by

    sizeof (wchar_t) before the comparison.

    Full check passes on x86-64 and build succeeds w/ and w/o multiarch.

    (cherry picked from commit b0969fa53a28b4ab2159806bf6c99a98999502ee)

diff --git a/string/test-strnlen.c b/string/test-strnlen.c

index bb5d9b5f04fa6586..eac84cd17526d5d9 100644

--- a/string/test-strnlen.c

+++ b/string/test-strnlen.c

@@ -75,7 +75,7 @@ do_test (size_t align, size_t len, size_t maxlen, int max_char)

 {

   size_t i;

-  align &= 63;

+  align &= (getpagesize () / sizeof (CHAR) - 1);

   if ((align + len) * sizeof (CHAR) >= page_size)

     return;

@@ -92,36 +92,50 @@ do_test (size_t align, size_t len, size_t maxlen, int max_char)

 static void

 do_overflow_tests (void)

 {

-  size_t i, j, len;

+  size_t i, j, al_idx, repeats, len;

   const size_t one = 1;

   uintptr_t buf_addr = (uintptr_t) buf1;

+  const size_t alignments[] = { 0, 1, 7, 9, 31, 33, 63, 65, 95, 97, 127, 129 };

-  for (i = 0; i < 750; ++i)

+  for (al_idx = 0; al_idx < sizeof (alignments) / sizeof (alignments[0]);

+       al_idx++)

     {

-      do_test (0, i, SIZE_MAX - i, BIG_CHAR);

-      do_test (0, i, i - buf_addr, BIG_CHAR);

-      do_test (0, i, -buf_addr - i, BIG_CHAR);

-      do_test (0, i, SIZE_MAX - buf_addr - i, BIG_CHAR);

-      do_test (0, i, SIZE_MAX - buf_addr + i, BIG_CHAR);

-

-      len = 0;

-      for (j = 8 * sizeof(size_t) - 1; j ; --j)

-        {

-          len |= one << j;

-          do_test (0, i, len - i, BIG_CHAR);

-          do_test (0, i, len + i, BIG_CHAR);

-          do_test (0, i, len - buf_addr - i, BIG_CHAR);

-          do_test (0, i, len - buf_addr + i, BIG_CHAR);

-

-          do_test (0, i, ~len - i, BIG_CHAR);

-          do_test (0, i, ~len + i, BIG_CHAR);

-          do_test (0, i, ~len - buf_addr - i, BIG_CHAR);

-          do_test (0, i, ~len - buf_addr + i, BIG_CHAR);

-

-          do_test (0, i, -buf_addr, BIG_CHAR);

-          do_test (0, i, j - buf_addr, BIG_CHAR);

-          do_test (0, i, -buf_addr - j, BIG_CHAR);

-        }

+      for (repeats = 0; repeats < 2; ++repeats)

+	{

+	  size_t align = repeats ? (getpagesize () - alignments[al_idx])

+				 : alignments[al_idx];

+	  align /= sizeof (CHAR);

+	  for (i = 0; i < 750; ++i)

+	    {

+	      do_test (align, i, SIZE_MAX, BIG_CHAR);

+

+	      do_test (align, i, SIZE_MAX - i, BIG_CHAR);

+	      do_test (align, i, i - buf_addr, BIG_CHAR);

+	      do_test (align, i, -buf_addr - i, BIG_CHAR);

+	      do_test (align, i, SIZE_MAX - buf_addr - i, BIG_CHAR);

+	      do_test (align, i, SIZE_MAX - buf_addr + i, BIG_CHAR);

+

+	      len = 0;

+	      for (j = 8 * sizeof (size_t) - 1; j; --j)

+		{

+		  len |= one << j;

+		  do_test (align, i, len, BIG_CHAR);

+		  do_test (align, i, len - i, BIG_CHAR);

+		  do_test (align, i, len + i, BIG_CHAR);

+		  do_test (align, i, len - buf_addr - i, BIG_CHAR);

+		  do_test (align, i, len - buf_addr + i, BIG_CHAR);

+

+		  do_test (align, i, ~len - i, BIG_CHAR);

+		  do_test (align, i, ~len + i, BIG_CHAR);

+		  do_test (align, i, ~len - buf_addr - i, BIG_CHAR);

+		  do_test (align, i, ~len - buf_addr + i, BIG_CHAR);

+

+		  do_test (align, i, -buf_addr, BIG_CHAR);

+		  do_test (align, i, j - buf_addr, BIG_CHAR);

+		  do_test (align, i, -buf_addr - j, BIG_CHAR);

+		}

+	    }

+	}

     }

 }

diff --git a/sysdeps/x86_64/multiarch/strlen-avx2.S b/sysdeps/x86_64/multiarch/strlen-avx2.S

index b282a75613bf52ab..4d7d68396bcd4049 100644

--- a/sysdeps/x86_64/multiarch/strlen-avx2.S

+++ b/sysdeps/x86_64/multiarch/strlen-avx2.S

@@ -542,14 +542,11 @@ L(return_vzeroupper):

 L(cross_page_less_vec):

 	tzcntl	%eax, %eax

 #  ifdef USE_AS_WCSLEN

-	/* NB: Multiply length by 4 to get byte count.  */

-	sall	$2, %esi

+	/* NB: Divide by 4 to convert from byte-count to length.  */

+	shrl	$2, %eax

 #  endif

 	cmpq	%rax, %rsi

 	cmovb	%esi, %eax

-#  ifdef USE_AS_WCSLEN

-	shrl	$2, %eax

-#  endif

 	VZEROUPPER_RETURN

 # endif