Re: [Xen-devel] [PATCH v2 2/2] xmalloc: add a Kconfig option to poison free pool memory

[Jan Beulich <JBeulich@xxxxxxxx>]

On 05.07.2019 11:02, Paul Durrant wrote:
> --- a/xen/Kconfig.debug
> +++ b/xen/Kconfig.debug
> @@ -105,6 +105,13 @@ config DEBUG_TRACE
>         either directly to the console or are printed to console in case of
>         a system crash.
>   
> +config XMEM_POOL_POISON
> +       bool "Poison free xenpool blocks"
> +       default DEBUG
> +       ---help---
> +      Poison free blocks with 0xAA bytes and verify them when a block is
> +      allocated in order to spot use-after-free issues.

There looks to be a spaces vs tabs problem here: Only the help
text has tabs for initial indentation.

> --- a/xen/common/xmalloc_tlsf.c
> +++ b/xen/common/xmalloc_tlsf.c
> @@ -238,6 +238,11 @@ static inline void EXTRACT_BLOCK(struct bhdr *b, struct 
> xmem_pool *p, int fl,
>           }
>       }
>       b->ptr.free_ptr = (struct free_ptr) {NULL, NULL};
> +#ifdef CONFIG_XMEM_POOL_POISON
> +    if ( (b->size & BLOCK_SIZE_MASK) > MIN_BLOCK_SIZE )
> +        ASSERT(!memchr_inv(b->ptr.buffer + MIN_BLOCK_SIZE, 0xAA,
> +                           (b->size & BLOCK_SIZE_MASK) - MIN_BLOCK_SIZE));
> +#endif /* CONFIG_XMEM_POOL_POISON */
>   }
>   
>   /**
> @@ -245,6 +250,11 @@ static inline void EXTRACT_BLOCK(struct bhdr *b, struct 
> xmem_pool *p, int fl,
>    */
>   static inline void INSERT_BLOCK(struct bhdr *b, struct xmem_pool *p, int 
> fl, int sl)
>   {
> +#ifdef CONFIG_XMEM_POOL_POISON
> +    if ( (b->size & BLOCK_SIZE_MASK) > MIN_BLOCK_SIZE )
> +        memset(b->ptr.buffer + MIN_BLOCK_SIZE, 0xAA,
> +               (b->size & BLOCK_SIZE_MASK) - MIN_BLOCK_SIZE);
> +#endif /* CONFIG_XMEM_POOL_POISON */

Can you tie together the two instances of 0xAA via a #define,
please?

It would also be nice if both #ifdef blocks were separated from
their neighboring code by a blank line, despite the file using
blank lines rather sparingly so far.

With the adjustments here I think it would be best if you could
also resend patch 1 with the slightly adjusted commit message.

Jan
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