Re: [PATCH] powerpc/kexec: Annotate umem_info members with __counted_by_ptr

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 30/07/26 18:32, Thorsten Blum wrote:
> Add __counted_by_ptr() to umem_info::buf and umem_info::ranges to
> improve access bounds checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
>
> Set the count fields before assigning the corresponding pointers, return
> early on krealloc() failure, and use sizeof(*buf) when deriving
> max_entries from the allocation size.
>
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>   arch/powerpc/kexec/file_load_64.c | 22 ++++++++++++----------
>   1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
> index 8c72e12ea44e..6424b668f0e9 100644
> --- a/arch/powerpc/kexec/file_load_64.c
> +++ b/arch/powerpc/kexec/file_load_64.c
> @@ -34,14 +34,15 @@
>   #include <asm/cputhreads.h>
>   
>   struct umem_info {
> -	__be64 *buf;		/* data buffer for usable-memory property */
> +	/* data buffer for usable-memory property */
> +	__be64 *buf __counted_by_ptr(max_entries);
>   	u32 size;		/* size allocated for the data buffer */
>   	u32 max_entries;	/* maximum no. of entries */
>   	u32 idx;		/* index of current entry */
>   
>   	/* usable memory ranges to look up */
>   	unsigned int nr_ranges;
> -	const struct range *ranges;
> +	const struct range *ranges __counted_by_ptr(nr_ranges);
>   };
[...]
>   
>   const struct kexec_file_ops * const kexec_file_loaders[] = {
> @@ -83,11 +84,12 @@ static __be64 *check_realloc_usable_mem(struct umem_info *um_info, int cnt)
>   
>   	new_size = um_info->size + MEM_RANGE_CHUNK_SZ;
>   	tbuf = krealloc(um_info->buf, new_size, GFP_KERNEL);
> -	if (tbuf) {
> -		um_info->buf = tbuf;
> -		um_info->size = new_size;
> -		um_info->max_entries = (um_info->size / sizeof(u64));
> -	}
> +	if (!tbuf)
> +		return NULL;
> +
> +	um_info->size = new_size;
> +	um_info->max_entries = um_info->size / sizeof(*um_info->buf);
> +	um_info->buf = tbuf;


Could you please explain why size and max_entries are updated before the 
buffer itself?

- Sourabh Jain


>   
>   	return tbuf;
>   }
> @@ -288,13 +290,13 @@ static int update_usable_mem_fdt(void *fdt, struct crash_mem *usable_mem)
>   		return -EINVAL;
>   	}
>   
> -	um_info.buf  = NULL;
>   	um_info.size = 0;
>   	um_info.max_entries = 0;
> -	um_info.idx  = 0;
> +	um_info.buf = NULL;
> +	um_info.idx = 0;
>   	/* Memory ranges to look up */
> -	um_info.ranges = &(usable_mem->ranges[0]);
>   	um_info.nr_ranges = usable_mem->nr_ranges;
> +	um_info.ranges = usable_mem->ranges;
>   
>   	dn = of_find_node_by_path("/ibm,dynamic-reconfiguration-memory");
>   	if (dn) {
>