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.

diff --git a/string/test-strnlen.c b/string/test-strnlen.c
index 4a9375112add204fa6466176ee18395ba42794ac..5cbaf4b73489f60b48150cb1a96c4c8fe62a93c2 100644 (file)
--- a/string/test-strnlen.c
+++ b/string/test-strnlen.c
@@ -73,7 +73,7 @@ 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;
 
@@ -90,38 +90,50 @@ 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 (1, i, SIZE_MAX, BIG_CHAR);
-
-      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 0593fb303b3068115b3fba15b1c15b01d44a3a0e..b9b58ef599c19d2b13f9ff27c8af4bfbffecb735 100644 (file)
--- a/sysdeps/x86_64/multiarch/strlen-avx2.S
+++ b/sysdeps/x86_64/multiarch/strlen-avx2.S
@@ -544,14 +544,11 @@ 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