Re: [PATCH v12 net-next 03/11] bpf: add lookup/update/delete/iterate methods to BPF maps

[David Miller <davem@davemloft.net>]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Mon, 15 Sep 2014 12:18:33 -0700

> @@ -83,6 +112,15 @@ union bpf_attr {
>  		__u32	value_size;	/* size of value in bytes */
>  		__u32	max_entries;	/* max number of entries in a map */
>  	};
> +
> +	struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
> +		int map_fd;
> +		void __user *key;
> +		union {
> +			void __user *value;
> +			void __user *next_key;
> +		};
> +	};
>  };
>  
>  #endif /* _UAPI__LINUX_BPF_H__ */

Depending upon the processor ABI, this change can increase the
alignment requirements of union bpf_attr.  So the structure is not
compatible between patch #1 and patch #3 here.

Also, you haven't implemented any compat layer whatsoever for the
necessary translations.  This happens because you are using pointers
which are different sized between 32-bit and 64-bit ABIs.

I would suggest you use instead something like "aligned_u64" since
these are just arbitrary userland cookies and using "aligned_u64"
vs. "u64" will make it so that you don't have to deal with the 64-bit
type alignment differences between x86-32 and x86-64 while writing the
compat wrappers (if any).