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Message-Id: <20230406212136.19716-1-kal.conley@dectris.com> Date: Thu, 6 Apr 2023 23:21:36 +0200 From: Kal Conley <kal.conley@...tris.com> To: Björn Töpel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com> Cc: Kal Conley <kal.conley@...tris.com>, netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH bpf-next] xsk: Elide base_addr comparison in xp_unaligned_validate_desc Remove redundant (base_addr >= pool->addrs_cnt) comparison from the conditional. In particular, addr is computed as: addr = base_addr + offset where base_addr and offset are stored as 48-bit and 16-bit unsigned integers, respectively. The above sum cannot overflow u64 since base_addr has a maximum value of 0x0000ffffffffffff and offset has a maximum value of 0xffff (implying a maximum sum of 0x000100000000fffe). Since overflow is impossible, it follows that addr >= base_addr. Now if (base_addr >= pool->addrs_cnt), then clearly: addr >= base_addr >= pool->addrs_cnt Thus, (base_addr >= pool->addrs_cnt) implies (addr >= pool->addrs_cnt). Subsequently, the former comparison is unnecessary in the conditional since for any boolean expressions A and B, (A || B) && (A -> B) is equivalent to B. Signed-off-by: Kal Conley <kal.conley@...tris.com> --- net/xdp/xsk_queue.h | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h index 66c6f57c9c44..016f3753180a 100644 --- a/net/xdp/xsk_queue.h +++ b/net/xdp/xsk_queue.h @@ -153,16 +153,14 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool, static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool, struct xdp_desc *desc) { - u64 addr, base_addr; - - base_addr = xp_unaligned_extract_addr(desc->addr); - addr = xp_unaligned_add_offset_to_addr(desc->addr); + u64 addr; if (desc->len > pool->chunk_size) return false; - if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt || - addr + desc->len > pool->addrs_cnt || + addr = xp_unaligned_add_offset_to_addr(desc->addr); + + if (addr >= pool->addrs_cnt || addr + desc->len > pool->addrs_cnt || xp_desc_crosses_non_contig_pg(pool, addr, desc->len)) return false; -- 2.39.2
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