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 <[email protected]>
---
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 66c6f57c9c44..dea4f378327d 100644
--- a/net/xdp/xsk_queue.h
+++ b/net/xdp/xsk_queue.h
@@ -153,16 +153,12 @@ 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;
--
2.39.2
On Tue, 11 Apr 2023 at 15:03, Kal Conley <[email protected]> wrote:
>
> 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.
Thanks Kal! Just checking again that you ran the xsk selftests on your
change and that it passed? If so, here is my ack.
Acked-by: Magnus Karlsson <[email protected]>
> Signed-off-by: Kal Conley <[email protected]>
> ---
> 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 66c6f57c9c44..dea4f378327d 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -153,16 +153,12 @@ 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;
>
> --
> 2.39.2
>
> Thanks Kal! Just checking again that you ran the xsk selftests on your
> change and that it passed? If so, here is my ack.
>
> Acked-by: Magnus Karlsson <[email protected]>
>
yep, I ran the tests and they PASSED.
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <[email protected]>:
On Tue, 11 Apr 2023 15:00:25 +0200 you wrote:
> Remove redundant (base_addr >= pool->addrs_cnt) comparison from the
> conditional.
>
> In particular, addr is computed as:
>
> addr = base_addr + offset
>
> [...]
Here is the summary with links:
- [bpf-next,v2] xsk: Elide base_addr comparison in xp_unaligned_validate_desc
https://git.kernel.org/bpf/bpf-next/c/1ba83f505c53
You are awesome, thank you!
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