From 1ba83f505c53d35eda892ac7f108ef1189da6fa8 Mon Sep 17 00:00:00 2001
From: Kal Conley <kal.conley@dectris.com>
Date: Tue, 11 Apr 2023 15:00:25 +0200
Subject: [PATCH] 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@dectris.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20230411130025.19704-1-kal.conley@dectris.com
---
net/xdp/xsk_queue.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
index 76b574bffd4a6..6d40a77fccbe9 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -149,16 +149,12 @@ 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 = xp_unaligned_add_offset_to_addr(desc->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 ||
+ if (addr >= pool->addrs_cnt || addr + desc->len > pool->addrs_cnt ||
xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
return false;
--
GitLab