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

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Message-Id: <20140916.151606.448751391205382097.davem@davemloft.net>
Date:	Tue, 16 Sep 2014 15:16:06 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	mingo@...nel.org, torvalds@...ux-foundation.org,
	luto@...capital.net, dborkman@...hat.com,
	hannes@...essinduktion.org, chema@...gle.com, edumazet@...gle.com,
	a.p.zijlstra@...llo.nl, pablo@...filter.org, hpa@...or.com,
	akpm@...ux-foundation.org, keescook@...omium.org,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 net-next 03/11] bpf: add
 lookup/update/delete/iterate methods to BPF maps

From: Alexei Starovoitov <ast@...mgrid.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).
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