Re: [PATCH v3 1/3] lib/test_kasan: Add bitops tests

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

On 5/31/19 6:08 PM, Marco Elver wrote:
> This adds bitops tests to the test_kasan module. In a follow-up patch,
> support for bitops instrumentation will be added.
> 
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> Changes in v3:
> * Use kzalloc instead of kmalloc.
> * Use sizeof(*bits).
> 
> Changes in v2:
> * Use BITS_PER_LONG.
> * Use heap allocated memory for test, as newer compilers (correctly)
>   warn on OOB stack access.
> ---
>  lib/test_kasan.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 72 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 7de2702621dc..1ef9702327d2 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -11,16 +11,17 @@
>  
>  #define pr_fmt(fmt) "kasan test: %s " fmt, __func__
>  
> +#include <linux/bitops.h>
>  #include <linux/delay.h>
> +#include <linux/kasan.h>
>  #include <linux/kernel.h>
> -#include <linux/mman.h>
>  #include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/module.h>
>  #include <linux/printk.h>
>  #include <linux/slab.h>
>  #include <linux/string.h>
>  #include <linux/uaccess.h>
> -#include <linux/module.h>
> -#include <linux/kasan.h>
>  
>  /*
>   * Note: test functions are marked noinline so that their names appear in
> @@ -623,6 +624,73 @@ static noinline void __init kasan_strings(void)
>  	strnlen(ptr, 1);
>  }
>  
> +static noinline void __init kasan_bitops(void)
> +{
> +	long *bits = kzalloc(sizeof(*bits), GFP_KERNEL);

It would be safer to do kzalloc(sizeof(*bits) + 1, GFP_KERNEL) and change tests accordingly to: set_bit(BITS_PER_LONG + 1, bits) ...
kmalloc will internally round up allocation to 16-bytes, so we won't be actually corrupting someone elses memory.


> +	if (!bits)
> +		return;
> +
> +	pr_info("within-bounds in set_bit");
> +	set_bit(0, bits);
> +
> +	pr_info("within-bounds in set_bit");
> +	set_bit(BITS_PER_LONG - 1, bits);


I'd remove these two. There are plenty of within bounds set_bit() in the kernel so they are well tested already.