From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 4BC6C36127 for ; Tue, 5 Nov 2024 03:50:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730778624; cv=none; b=lATTG7+BrNbM5pYrZcNvKsarPlCkeq75dIaPDhCayeUpNehMcpyyiW7/JnPH011Z+btaAvIB+qwuQyYZspHHXs4rgRuBcRJ0+p0/lL/7GvCh3cGat1TOpPATkkdxX3135jqgaLJfqxuSSRNpAU9bY068KmFTPyl3oQkeDMYbTuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730778624; c=relaxed/simple; bh=z4Z3nj5bTcX4whZwFtOMLhiWuLxftDLn4iVz9iVaP0g=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=bZvIjQKALonjz4VrAPq4QBTtW+Y1KCMUnUivuNoL1DOyWMvsX8jhmv4gZjvOurgA+8Uc3898d4TCfqnQmFgcnU81C3pnFKY6/JuiF2Q/w+d/WzEckOlo9bz7gQ6Vm3HPLiXNquayHl0x5U3ZrMivxilB7bJaz8Kxke4wjxg8rSk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=U9iuhtwq; arc=none smtp.client-ip=95.215.58.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="U9iuhtwq" Message-ID: <29e2658c-02c9-4ef1-a633-ee5017e72bc3@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1730778616; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Bn6BLaHbRtRjRJdwRqG8uQFIFn47AXGrC8vrstPkl6I=; b=U9iuhtwq9sDUddPYffKoNmfnNMo8p1POrwBe4+bx2mwxdcbCZfl/fB5GK5FN1TtjZKapgc IH5Hr7zRBGZKG3LSTKcT13a6e8HYIQUzf9WVJOw04mvo49U4C0q7jO9NQ6gYNQx7DvEFxH /YJu8WXAu3YSUJRy69Mbtt51JooDXNA= Date: Mon, 4 Nov 2024 19:50:08 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v9 02/10] bpf: Return false for bpf_prog_check_recur() default case Content-Language: en-GB X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song To: Alexei Starovoitov Cc: bpf , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Kernel Team , Martin KaFai Lau , Tejun Heo References: <20241104193455.3241859-1-yonghong.song@linux.dev> <20241104193505.3242662-1-yonghong.song@linux.dev> <36294e71-4d0b-465d-9bf5-c5640aa3a089@linux.dev> <6c78f973-341e-4260-aed4-a5cb8e873acc@linux.dev> In-Reply-To: <6c78f973-341e-4260-aed4-a5cb8e873acc@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 11/4/24 6:53 PM, Yonghong Song wrote: > > On 11/4/24 5:55 PM, Alexei Starovoitov wrote: >> On Mon, Nov 4, 2024 at 5:35 PM Yonghong Song >> wrote: >>> >>> On 11/4/24 5:21 PM, Alexei Starovoitov wrote: >>>> On Mon, Nov 4, 2024 at 11:35 AM Yonghong Song >>>> wrote: >>>>> The bpf_prog_check_recur() funciton is currently used by trampoline >>>>> and tracing programs (also using trampoline) to check whether a >>>>> particular prog supports recursion checking or not. The default case >>>>> (non-trampoline progs) return true in the current implementation. >>>>> >>>>> Let us make the non-trampoline prog recursion check return false >>>>> instead. It does not impact any existing use cases and allows the >>>>> function to be used outside the trampoline context in the next patch. >>>> Does not impact ?! But it does. >>>> This patch removes recursion check from fentry progs. >>>> This cannot be right. >>> The original bpf_prog_check_recur() implementation: >>> >>> static inline bool bpf_prog_check_recur(const struct bpf_prog *prog) >>> { >>>           switch (resolve_prog_type(prog)) { >>>           case BPF_PROG_TYPE_TRACING: >>>                   return prog->expected_attach_type != BPF_TRACE_ITER; >>>           case BPF_PROG_TYPE_STRUCT_OPS: >>>           case BPF_PROG_TYPE_LSM: >>>                   return false; >>>           default: >>>                   return true; >>>           } >>> } >>> >>> fentry prog is a TRACING prog, so it is covered. Did I miss anything? >> I see. This is way too subtle. >> You're correct that fentry is TYPE_TRACING, >> so it could have "worked" if it was used to build trampolines only. >> >> But this helper is called for other prog types: >> >>          case BPF_FUNC_task_storage_get: >>                  if (bpf_prog_check_recur(prog)) >>                          return &bpf_task_storage_get_recur_proto; >>                  return &bpf_task_storage_get_proto; >> >> so it's still not correct, but for a different reason. > > There are four uses for func bpf_prog_check_recur() in kernel based on > cscope: 0 kernel/bpf/trampoline.c bpf_trampoline_enter 1053 if > (bpf_prog_check_recur(prog)) 1 kernel/bpf/trampoline.c > bpf_trampoline_exit 1068 if (bpf_prog_check_recur(prog)) 2 > kernel/trace/bpf_trace.c bpf_tracing_func_proto 1549 if > (bpf_prog_check_recur(prog)) 3 kernel/trace/bpf_trace.c > bpf_tracing_func_proto 1553 if (bpf_prog_check_recur(prog)) The 2nd > and 3rd ones are in bpf_trace.c. 1444 static const struct > bpf_func_proto * 1445 bpf_tracing_func_proto(enum bpf_func_id func_id, > const struct bpf_prog *prog) 1446 { 1447 switch (func_id) { ... 1548 > case BPF_FUNC_task_storage_get: 1549 if (bpf_prog_check_recur(prog)) > 1550 return &bpf_task_storage_get_recur_proto; 1551 return > &bpf_task_storage_get_proto; 1552 case BPF_FUNC_task_storage_delete: > 1553 if (bpf_prog_check_recur(prog)) 1554 return > &bpf_task_storage_delete_recur_proto; 1555 return > &bpf_task_storage_delete_proto; ... 1568 default: 1569 return > bpf_base_func_proto(func_id, prog); 1570 } 1571 } They are used for > tracing programs. So we should be safe here. But if you think that > changing bpf_proc_check_recur() and calling function > bpf_prog_check_recur() in bpf_enable_priv_stack() is too subtle, I can > go back to my original approach which makes all supported prog types > explicit in bpf_enable_priv_stack(). Sorry. Format issue again. The below is a better format: There are four uses for func bpf_prog_check_recur() in kernel based on cscope: 0 kernel/bpf/trampoline.c bpf_trampoline_enter 1053 if (bpf_prog_check_recur(prog)) 1 kernel/bpf/trampoline.c bpf_trampoline_exit 1068 if (bpf_prog_check_recur(prog)) 2 kernel/trace/bpf_trace.c bpf_tracing_func_proto 1549 if (bpf_prog_check_recur(prog)) 3 kernel/trace/bpf_trace.c bpf_tracing_func_proto 1553 if (bpf_prog_check_recur(prog)) The 2nd and 3rd ones are in bpf_trace.c. 1444 static const struct bpf_func_proto * 1445 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) 1446 { 1447     switch (func_id) { ... 1548     case BPF_FUNC_task_storage_get: 1549         if (bpf_prog_check_recur(prog)) 1550             return &bpf_task_storage_get_recur_proto; 1551         return &bpf_task_storage_get_proto; 1552     case BPF_FUNC_task_storage_delete: 1553         if (bpf_prog_check_recur(prog)) 1554             return &bpf_task_storage_delete_recur_proto; 1555         return &bpf_task_storage_delete_proto; ... 1568     default: 1569         return bpf_base_func_proto(func_id, prog); 1570     } 1571 } They are used for tracing programs. So we should be safe here. But if you think that changing bpf_proc_check_recur() and calling function bpf_prog_check_recur() in bpf_enable_priv_stack() is too subtle, I can go back to my original approach which makes all supported prog types explicit in bpf_enable_priv_stack().