From: Martin KaFai Lau <martin.lau@linux.dev>
To: Yonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
kernel-team@fb.com, Martin KaFai Lau <martin.lau@kernel.org>,
bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v9 0/4] bpf: Add bpf_rcu_read_lock() support
Date: Wed, 23 Nov 2022 15:30:33 -0800 [thread overview]
Message-ID: <0bb01f0e-c19f-ad96-80e8-a51679f170c8@linux.dev> (raw)
In-Reply-To: <20221123045350.2322811-1-yhs@fb.com>
On 11/22/22 8:53 PM, Yonghong Song wrote:
> Currently, without rcu attribute info in BTF, the verifier treats
> rcu tagged pointer as a normal pointer. This might be a problem
> for sleepable program where rcu_read_lock()/unlock() is not available.
> For example, for a sleepable fentry program, if rcu protected memory
> access is interleaved with a sleepable helper/kfunc, it is possible
> the memory access after the sleepable helper/kfunc might be invalid
> since the object might have been freed then. Even without
> a sleepable helper/kfunc, without rcu_read_lock() protection,
> it is possible that the rcu protected object might be release
> in the middle of bpf program execution which may cause incorrect
> result.
>
> To prevent above cases, enable btf_type_tag("rcu") attributes,
> introduce new bpf_rcu_read_lock/unlock() kfuncs and add verifier support.
>
> In the rest of patch set, Patch 1 enabled btf_type_tag for __rcu
> attribute. Patche 2 added might_sleep in bpf_func_proto. Patch 3 added new
> bpf_rcu_read_lock/unlock() kfuncs and verifier support.
> Patch 4 added some tests for these two new kfuncs.
>
> Changelogs:
> v8 -> v9:
> . remove sleepable prog check for ld_abs/ind checking in rcu read
> lock region.
> . fix a test failure with gcc-compiled kernel.
> . a couple of other minor fixes.
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
prev parent reply other threads:[~2022-11-23 23:30 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-23 4:53 [PATCH bpf-next v9 0/4] bpf: Add bpf_rcu_read_lock() support Yonghong Song
2022-11-23 4:53 ` [PATCH bpf-next v9 1/4] compiler_types: Define __rcu as __attribute__((btf_type_tag("rcu"))) Yonghong Song
2022-11-23 4:54 ` [PATCH bpf-next v9 2/4] bpf: Introduce might_sleep field in bpf_func_proto Yonghong Song
2022-11-23 4:54 ` [PATCH bpf-next v9 3/4] bpf: Add kfunc bpf_rcu_read_lock/unlock() Yonghong Song
2022-11-23 23:32 ` Martin KaFai Lau
2022-11-24 1:40 ` Alexei Starovoitov
2022-11-24 2:57 ` Yonghong Song
2022-11-24 4:09 ` Alexei Starovoitov
2022-11-24 5:16 ` Yonghong Song
2022-11-23 4:54 ` [PATCH bpf-next v9 4/4] selftests/bpf: Add tests for bpf_rcu_read_lock() Yonghong Song
2022-11-23 23:30 ` Martin KaFai Lau [this message]
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