From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A571D613B for ; Thu, 11 May 2023 15:57:53 +0000 (UTC) Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A7E840E4 for ; Thu, 11 May 2023 08:57:52 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id 3f1490d57ef6-ba2d0b391d3so11211585276.2 for ; Thu, 11 May 2023 08:57:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1683820672; x=1686412672; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=Y/pyPNy9qZZ+kH0++6rFd1D1h7SDPYk2nW4BjP//A1I=; b=pgm/3civrevUYpU/KFDdajU9IIsKus2s553qkydi8MKFJyZq7jacMwlrDhU6l8G+L/ Spnl/hAw1bMqIXKqniXrHLDdZg8cy4I9mjbIuIiRFAlxID79t+9Wlp+nYpyE7lOPzZlO GT7BdDzeEKcdCFw5SVDFl3Gf/fiaSVcd0ixUbX8lG53ps+PV5mJl3fA1QTw/tvGsfN1p aJJUyobNczJy1pqsIAOC/nce3IyzNgQps2QlndLvYOXfTau8Qj6bvi4uvBIAj05HkaIw PSPXzW21owRyQXKCQ8/kJ8XInvRftjgyis0PYs0cMwRk4Wc6LMO8JoWYEgKjpk7rQKoB JB3A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1683820672; x=1686412672; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=Y/pyPNy9qZZ+kH0++6rFd1D1h7SDPYk2nW4BjP//A1I=; b=YS018vsKPxJUOp+PWTNeQUKCfro5J86KbtxevbuZGJz5CXwU0TPbdDKqo7PmPfSWRk G/j2hfU9rMjv4SsmDYmlK1TLcKlZaBx4Gy7w+bZLz0wNAW3bLiWjgN5fYl3/B0jF/E0N Xc8pBr4LafCATl9I2+FTF870ta4bruXrOuKlQtZ4r3dYq1hBa5cOHfb2OEfxp11XRqvz IhztgVCOSCqcO+3698UimoTmalobM7VSXLSaR1n6aVER8KAHaACxyHjrw0tMzOXQC5a/ 1HGZa8FJraT27BSAk+1bCXtMaAa9vp3yn9plW2eEYUfFFWSqKW4fedy7O8tdUdx2dIap DTtA== X-Gm-Message-State: AC+VfDxXtET8iPfEBgFc7Je5j3DSEZt7EzHiMafxqTOZ5UypYqlKCM+E 1o965UmjZa7jUE6xtwtwRz9eFlLJoGYOvJe/vYbVFDwLrevFdaqWJ8zzgE3y6DkDOkZz3IjI1V6 ZmqOFIsVDSPXUdSw4+2MlMBKIRqpknRdBwni7VdyLRq8GUeuPLA== X-Google-Smtp-Source: ACHHUZ4Wx+lgthJVPUBgyCz2JuK2/covIwQqoMqteHyLGcmpvQFBpBtFv4O4Gt6KU0iydh7qmIQwaMY= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a25:5f48:0:b0:b9e:6346:514b with SMTP id h8-20020a255f48000000b00b9e6346514bmr13230815ybm.4.1683820671762; Thu, 11 May 2023 08:57:51 -0700 (PDT) Date: Thu, 11 May 2023 08:57:40 -0700 In-Reply-To: <20230511155740.902548-1-sdf@google.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20230511155740.902548-1-sdf@google.com> X-Mailer: git-send-email 2.40.1.521.gf1e218fcd8-goog Message-ID: <20230511155740.902548-6-sdf@google.com> Subject: [PATCH bpf-next v5 4/4] bpf: Document EFAULT changes for sockopt From: Stanislav Fomichev To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-9.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net And add examples for how to correctly handle large optlens. This is less relevant now when we don't EFAULT anymore, but that's still the correct thing to do. Signed-off-by: Stanislav Fomichev --- Documentation/bpf/prog_cgroup_sockopt.rst | 57 ++++++++++++++++++++++- 1 file changed, 56 insertions(+), 1 deletion(-) diff --git a/Documentation/bpf/prog_cgroup_sockopt.rst b/Documentation/bpf/prog_cgroup_sockopt.rst index 172f957204bf..1226a94af07a 100644 --- a/Documentation/bpf/prog_cgroup_sockopt.rst +++ b/Documentation/bpf/prog_cgroup_sockopt.rst @@ -98,10 +98,65 @@ When the ``optval`` is greater than the ``PAGE_SIZE``, the BPF program indicates that the kernel should use BPF's trimmed ``optval``. When the BPF program returns with the ``optlen`` greater than -``PAGE_SIZE``, the userspace will receive ``EFAULT`` errno. +``PAGE_SIZE``, the userspace will receive original kernel +buffers without any modifications that the BPF program might have +applied. Example ======= +Recommended way to handle BPF programs is as follows: + +.. code-block:: c + + SEC("cgroup/getsockopt") + int getsockopt(struct bpf_sockopt *ctx) + { + /* Custom socket option. */ + if (ctx->level == MY_SOL && ctx->optname == MY_OPTNAME) { + ctx->retval = 0; + optval[0] = ...; + ctx->optlen = 1; + return 1; + } + + /* Modify kernel's socket option. */ + if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) { + ctx->retval = 0; + optval[0] = ...; + ctx->optlen = 1; + return 1; + } + + /* optval larger than PAGE_SIZE use kernel's buffer. */ + if (ctx->optlen > PAGE_SIZE) + ctx->optlen = 0; + + return 1; + } + + SEC("cgroup/setsockopt") + int setsockopt(struct bpf_sockopt *ctx) + { + /* Custom socket option. */ + if (ctx->level == MY_SOL && ctx->optname == MY_OPTNAME) { + /* do something */ + ctx->optlen = -1; + return 1; + } + + /* Modify kernel's socket option. */ + if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) { + optval[0] = ...; + return 1; + } + + /* optval larger than PAGE_SIZE use kernel's buffer. */ + if (ctx->optlen > PAGE_SIZE) + ctx->optlen = 0; + + return 1; + } + See ``tools/testing/selftests/bpf/progs/sockopt_sk.c`` for an example of BPF program that handles socket options. -- 2.40.1.521.gf1e218fcd8-goog