* [PATCH] bpf: btf: Fix a var size check in validator
@ 2022-01-08 2:22 Yichun Zhang (agentzh)
2022-01-08 18:53 ` Yonghong Song
0 siblings, 1 reply; 2+ messages in thread
From: Yichun Zhang (agentzh) @ 2022-01-08 2:22 UTC (permalink / raw)
To: yichun
Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend,
KP Singh, Nathan Chancellor, Nick Desaulniers, netdev, bpf,
linux-kernel, llvm
The btf validator should croak when the variable size is larger than
its type size, not less. The LLVM optimizer may use smaller sizes for
the C type.
We ran into this issue with real-world BPF programs emitted by the
latest version of Clang/LLVM.
Fixes: 1dc92851849cc ("bpf: kernel side support for BTF Var and DataSec")
Signed-off-by: Yichun Zhang (agentzh) <yichun@openresty.com>
---
kernel/bpf/btf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 9bdb03767db5..2a6967b13ce1 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3696,7 +3696,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env,
return -EINVAL;
}
- if (vsi->size < type_size) {
+ if (vsi->size > type_size) {
btf_verifier_log_vsi(env, v->t, vsi, "Invalid size");
return -EINVAL;
}
--
2.17.2
^ permalink raw reply [flat|nested] 2+ messages in thread* Re: [PATCH] bpf: btf: Fix a var size check in validator
2022-01-08 2:22 [PATCH] bpf: btf: Fix a var size check in validator Yichun Zhang (agentzh)
@ 2022-01-08 18:53 ` Yonghong Song
0 siblings, 0 replies; 2+ messages in thread
From: Yonghong Song @ 2022-01-08 18:53 UTC (permalink / raw)
To: Yichun Zhang (agentzh)
Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Song Liu, John Fastabend, KP Singh,
Nathan Chancellor, Nick Desaulniers, netdev, bpf, linux-kernel,
llvm
On 1/7/22 6:22 PM, Yichun Zhang (agentzh) wrote:
> The btf validator should croak when the variable size is larger than
> its type size, not less. The LLVM optimizer may use smaller sizes for
> the C type.
>
> We ran into this issue with real-world BPF programs emitted by the
> latest version of Clang/LLVM.
Could you give an example to show we have variable size is less than
type_size?
>
> Fixes: 1dc92851849cc ("bpf: kernel side support for BTF Var and DataSec")
> Signed-off-by: Yichun Zhang (agentzh) <yichun@openresty.com>
> ---
> kernel/bpf/btf.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 9bdb03767db5..2a6967b13ce1 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3696,7 +3696,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env,
> return -EINVAL;
> }
>
> - if (vsi->size < type_size) {
> + if (vsi->size > type_size) {
> btf_verifier_log_vsi(env, v->t, vsi, "Invalid size");
> return -EINVAL;
> }
The fix is incorrect. We do have cases where variable size greater than
type_size. For example,
$ cat t.c
struct t {
int g;
char a[];
} v = {1, {'a', 'b', 'c', 0}};
The type (struct t) size is 4, but the variable size is 8.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-01-08 18:53 ` Yonghong Song
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