netdev - [RFC PATCH net-next 1/6] bpf: Access hwtstamp field of hwtstamps directly

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Date:   Sun,  6 Mar 2022 09:56:53 +0100
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     richardcochran@...il.com, yangbo.lu@....com, davem@...emloft.net,
        kuba@...nel.org
Cc:     mlichvar@...hat.com, vinicius.gomes@...el.com,
        netdev@...r.kernel.org,
        Gerhard Engleder <gerhard@...leder-embedded.com>
Subject: [RFC PATCH net-next 1/6] bpf: Access hwtstamp field of hwtstamps directly

skb_shared_hwtstamps contains only the field hwtstamp. That property is
hard-coded and checked during build in BPF. bpf_target_off() gets the
whole structure as argument (hwtstamps) instead of the actually accessed
field hwtstamp.

Access hwtstamp field directly and allow future extensions of
skb_shared_hwtstamps.

Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
---
 net/core/filter.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 88767f7da150..09e202b60060 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -9364,13 +9364,12 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
 		break;
 	case offsetof(struct __sk_buff, hwtstamp):
 		BUILD_BUG_ON(sizeof_field(struct skb_shared_hwtstamps, hwtstamp) != 8);
-		BUILD_BUG_ON(offsetof(struct skb_shared_hwtstamps, hwtstamp) != 0);
 
 		insn = bpf_convert_shinfo_access(si, insn);
 		*insn++ = BPF_LDX_MEM(BPF_DW,
 				      si->dst_reg, si->dst_reg,
 				      bpf_target_off(struct skb_shared_info,
-						     hwtstamps, 8,
+						     hwtstamps.hwtstamp, 8,
 						     target_size));
 		break;
 	}
-- 
2.20.1