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Date:   Wed, 23 Nov 2022 15:30:33 -0800
MIME-Version: 1.0
Subject: Re: [PATCH bpf-next v9 0/4] bpf: Add bpf_rcu_read_lock() support
Content-Language: en-US
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
References: <20221123045350.2322811-1-yhs@fb.com>
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From:   Martin KaFai Lau <martin.lau@linux.dev>
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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>