lkdtm/heap: Hide allocation size from -Warray-bounds

With the kmalloc() size annotations, GCC is smart enough to realize that
LKDTM is intentionally writing past the end of the buffer. This is on
purpose, of course, so hide the buffer from the optimizer. Silences:

../drivers/misc/lkdtm/heap.c: In function 'lkdtm_SLAB_LINEAR_OVERFLOW':
../drivers/misc/lkdtm/heap.c:59:13: warning: array subscript 256 is outside array bounds of 'void[1020]' [-Warray-bounds]
   59 |         data[1024 / sizeof(u32)] = 0x12345678;
      |         ~~~~^~~~~~~~~~~~~~~~~~~~
In file included from ../drivers/misc/lkdtm/heap.c:7:
In function 'kmalloc',
    inlined from 'lkdtm_SLAB_LINEAR_OVERFLOW' at ../drivers/misc/lkdtm/heap.c:54:14:
../include/linux/slab.h:581:24: note: at offset 1024 into object of size 1020 allocated by 'kmem_cache_alloc_trace'
  581 |                 return kmem_cache_alloc_trace(
      |                        ^~~~~~~~~~~~~~~~~~~~~~~
  582 |                                 kmalloc_caches[kmalloc_type(flags)][index],
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  583 |                                 flags, size);
      |                                 ~~~~~~~~~~~~

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c
index 5d3b92cd23bd612509ffda71f57f79e08d750214..62516078a619f9408f06077dc7e45107fbdf6f64 100644 (file)
--- a/drivers/misc/lkdtm/heap.c
+++ b/drivers/misc/lkdtm/heap.c
@@ -56,6 +56,7 @@ static void lkdtm_SLAB_LINEAR_OVERFLOW(void)
                return;
 
        pr_info("Attempting slab linear overflow ...\n");
+       OPTIMIZER_HIDE_VAR(data);
        data[1024 / sizeof(u32)] = 0x12345678;
        kfree(data);
 }