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AJvYcCVgRedg+zTDSjcM72iDUZqlnSkaXIu/lnbXdQWwjKLO+/35Q5qOahRrXkmMkYK3Z6jopxI=@vger.kernel.org X-Gm-Message-State: AOJu0YwEMuFkUV2pYPl4+57jQmsTGZQlOqqNE5s8CIlHA3ZeWtiLJPeF sylhqYKrT11ANYSboETyqR8EMWk90Gcxr0UnT6cxeHhlRsNm8PFnWM+zWvzCK0BBWacddMEBIQ= = X-Google-Smtp-Source: AGHT+IG9mRl6GExluYMkHBV45dwKpB6OXH/vz/+odQj2Yxo5GTjngyEuQTo0iu+v+9DVqfFoPyEKI6ujFQ== X-Received: from edbca17.prod.google.com ([2002:aa7:cd71:0:b0:5cf:db39:7001]) (user=elver job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6402:2353:b0:5cf:d198:2a54 with SMTP id 4fb4d7f45d1cf-5d080c56e0cmr8017762a12.19.1732870846213; Fri, 29 Nov 2024 01:00:46 -0800 (PST) Date: Fri, 29 Nov 2024 09:59:33 +0100 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241129090040.2690691-1-elver@google.com> Subject: [PATCH bpf-next v4 1/2] bpf: Remove bpf_probe_write_user() warning message From: Marco Elver To: elver@google.com, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Nikola Grcevski , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net The warning message for bpf_probe_write_user() was introduced in 96ae52279594 ("bpf: Add bpf_probe_write_user BPF helper to be called in tracers"), with the following in the commit message: Given this feature is meant for experiments, and it has a risk of crashing the system, and running programs, we print a warning on when a proglet that attempts to use this helper is installed, along with the pid and process name. After 8 years since 96ae52279594, bpf_probe_write_user() has found successful applications beyond experiments [1, 2], with no other good alternatives. Despite its intended purpose for "experiments", that doesn't stop Hyrum's law, and there are likely many more users depending on this helper: "[..] it does not matter what you promise [..] all observable behaviors of your system will be depended on by somebody." The ominous "helper that may corrupt user memory!" has offered no real benefit, and has been found to lead to confusion where the system administrator is loading programs with valid use cases. As such, remove the warning message. Link: https://lore.kernel.org/lkml/20240404190146.1898103-1-elver@google.com/ [1] Link: https://lore.kernel.org/r/lkml/CAAn3qOUMD81-vxLLfep0H6rRd74ho2VaekdL4HjKq+Y1t9KdXQ@mail.gmail.com/ [2] Link: https://lore.kernel.org/all/CAEf4Bzb4D_=zuJrg3PawMOW3KqF8JvJm9SwF81_XHR2+u5hkUg@mail.gmail.com/ Signed-off-by: Marco Elver Acked-by: Jiri Olsa --- v3: * Collect Ack from Jiri. v2: * Just delete the message entirely (suggested by Andrii Nakryiko) --- kernel/trace/bpf_trace.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 630b763e5240..0ab56af2e298 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -362,9 +362,6 @@ static const struct bpf_func_proto *bpf_get_probe_write_proto(void) if (!capable(CAP_SYS_ADMIN)) return NULL; - pr_warn_ratelimited("%s[%d] is installing a program with bpf_probe_write_user helper that may corrupt user memory!", - current->comm, task_pid_nr(current)); - return &bpf_probe_write_user_proto; } From patchwork Fri Nov 29 08:59:34 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marco Elver X-Patchwork-Id: 13888496 X-Patchwork-Delegate: bpf@iogearbox.net Received: from mail-ej1-f74.google.com (mail-ej1-f74.google.com [209.85.218.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 58195143C40 for ; Fri, 29 Nov 2024 09:00:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732870852; cv=none; b=N6jN7KIarGiqWG5EVjfpPKzATpfItGgc47mcweZ41Fpj0r+p3+Q78F8UQX2N3R3m23lnavlE+MojSbG3L/wTQxjYGm6ivEmNJg/Yz89UNHu6FcDSEC3JQm5N7ljsds/dFXe7EIeC50k7U1Kb31axt5PLnkUQG2yW7MnWMHoXcUg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732870852; c=relaxed/simple; bh=xEslxxsKiLFjjUwGtii3ivKf92ut0unGtMTc00chBhg=; 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AJvYcCVLJkZSdljyplvt5Wc1jsyvkK1ncufTSpkW4YeRPY4cNdDZ62J2qrkIRMwEWDg+/z1ezss=@vger.kernel.org X-Gm-Message-State: AOJu0YyAA6HBz9H1tzR2pdHFSD4dy/a5wGyYar6mqhMPU423FrywjM6C A5naZChctEJLcIlzTyOClj4wDKNuMu1q6EQi8qV5o+MnO3kph2VTeg1wvU4JkLlvfAZCELWb9A= = X-Google-Smtp-Source: AGHT+IGHXhcpcjgkHjA0k7hYdLh0VcYJ721uO/6wKXB9uB8gEZqYP0S/2HCU0HVINTTx/wAZ9JlKx76g5w== X-Received: from ejca24.prod.google.com ([2002:a17:906:3698:b0:aa5:2ede:53bf]) (user=elver job=prod-delivery.src-stubby-dispatcher) by 2002:a17:906:d513:b0:aa5:199f:2bf2 with SMTP id a640c23a62f3a-aa580f56baamr1006472966b.29.1732870848742; Fri, 29 Nov 2024 01:00:48 -0800 (PST) Date: Fri, 29 Nov 2024 09:59:34 +0100 In-Reply-To: <20241129090040.2690691-1-elver@google.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241129090040.2690691-1-elver@google.com> X-Mailer: git-send-email 2.47.0.338.g60cca15819-goog Message-ID: <20241129090040.2690691-2-elver@google.com> Subject: [PATCH bpf-next v4 2/2] bpf: Refactor bpf_tracing_func_proto() and remove bpf_get_probe_write_proto() From: Marco Elver To: elver@google.com, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Nikola Grcevski , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net With bpf_get_probe_write_proto() no longer printing a message, we can avoid it being a special case with its own permission check. Refactor bpf_tracing_func_proto() similar to bpf_base_func_proto() to have a section conditional on bpf_token_capable(CAP_SYS_ADMIN), where the proto for bpf_probe_write_user() is returned. Finally, remove the unnecessary bpf_get_probe_write_proto(). This simplifies the code, and adding additional CAP_SYS_ADMIN-only helpers in future avoids duplicating the same CAP_SYS_ADMIN check. Suggested-by: Andrii Nakryiko Signed-off-by: Marco Elver Acked-by: Jiri Olsa --- v4: * Call bpf_base_func_proto() before bpf_token_capable() (no protos after should override bpf_base_func_proto() protos), so we can avoid indenting the switch-block after bpf_token_capable() (suggested by Alexei). v3: * Fix where bpf_base_func_proto() is called - it needs to be last, because we may override protos (as is e.g. done for BPF_FUNC_get_smp_processor_id). v2: * New patch. --- kernel/trace/bpf_trace.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 0ab56af2e298..b07d8067aa6e 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -357,14 +357,6 @@ static const struct bpf_func_proto bpf_probe_write_user_proto = { .arg3_type = ARG_CONST_SIZE, }; -static const struct bpf_func_proto *bpf_get_probe_write_proto(void) -{ - if (!capable(CAP_SYS_ADMIN)) - return NULL; - - return &bpf_probe_write_user_proto; -} - #define MAX_TRACE_PRINTK_VARARGS 3 #define BPF_TRACE_PRINTK_SIZE 1024 @@ -1417,6 +1409,8 @@ late_initcall(bpf_key_sig_kfuncs_init); static const struct bpf_func_proto * bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) { + const struct bpf_func_proto *func_proto; + switch (func_id) { case BPF_FUNC_map_lookup_elem: return &bpf_map_lookup_elem_proto; @@ -1458,9 +1452,6 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_perf_event_read_proto; case BPF_FUNC_get_prandom_u32: return &bpf_get_prandom_u32_proto; - case BPF_FUNC_probe_write_user: - return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ? - NULL : bpf_get_probe_write_proto(); case BPF_FUNC_probe_read_user: return &bpf_probe_read_user_proto; case BPF_FUNC_probe_read_kernel: @@ -1539,7 +1530,22 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) case BPF_FUNC_trace_vprintk: return bpf_get_trace_vprintk_proto(); default: - return bpf_base_func_proto(func_id, prog); + break; + } + + func_proto = bpf_base_func_proto(func_id, prog); + if (func_proto) + return func_proto; + + if (!bpf_token_capable(prog->aux->token, CAP_SYS_ADMIN)) + return NULL; + + switch (func_id) { + case BPF_FUNC_probe_write_user: + return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ? + NULL : &bpf_probe_write_user_proto; + default: + return NULL; } }