diff mbox series

[bpf-next,v5,2/5] bpf: tcp: Mark bpf_load_hdr_opt() arg2 as read-write

Message ID 3de5c7e513e3161e040ee0ad6eb8cc4b7d71aa4c.1734045451.git.dxu@dxuuu.xyz (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Support eliding map lookup nullness | expand

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Commit Message

Daniel Xu Dec. 12, 2024, 11:22 p.m. UTC 
MEM_WRITE attribute is defined as: "Non-presence of MEM_WRITE means that
MEM is only being read". bpf_load_hdr_opt() both reads and writes from
its arg2 - void *search_res.

This matters a lot for the next commit where we more precisely track
stack accesses. Without this annotation, the verifier will make false
assumptions about the contents of memory written to by helpers and
possibly prune valid branches.

Fixes: 6fad274f06f0 ("bpf: Add MEM_WRITE attribute")
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Martin KaFai Lau Dec. 16, 2024, 6:18 p.m. UTC | #1 
On 12/12/24 3:22 PM, Daniel Xu wrote:
> MEM_WRITE attribute is defined as: "Non-presence of MEM_WRITE means that
> MEM is only being read". bpf_load_hdr_opt() both reads and writes from
> its arg2 - void *search_res.
> 
> This matters a lot for the next commit where we more precisely track
> stack accesses. Without this annotation, the verifier will make false
> assumptions about the contents of memory written to by helpers and
> possibly prune valid branches.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
diff mbox series

Patch

diff --git a/net/core/filter.c b/net/core/filter.c
index 6625b3f563a4..09b5cd88e60d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7643,7 +7643,7 @@  static const struct bpf_func_proto bpf_sock_ops_load_hdr_opt_proto = {
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_CTX,
-	.arg2_type	= ARG_PTR_TO_MEM,
+	.arg2_type	= ARG_PTR_TO_MEM | MEM_WRITE,
 	.arg3_type	= ARG_CONST_SIZE,
 	.arg4_type	= ARG_ANYTHING,
 };