From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta1.migadu.com (out-179.mta1.migadu.com [95.215.58.179]) (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 B968A18E030 for ; Tue, 5 Nov 2024 06:02:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730786547; cv=none; b=r5Zr3bWlXkHr+oRtcNBRr6pG3ypePzhVqmYbSUbXdsOIYh2k3FI0IkiOdlV1xjShZd48JH979L8ljSeuRRfyJlGi8nx8pBOjtpTLErTzIfjh0JTfIMV2FVeA2e+7lud3tMzPpCzLrFFPNZOeiUG1LHyFEFa0AvqhDGK+FWwpYeQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730786547; c=relaxed/simple; bh=lvOlIpB5XChXqQE1OQysf49Ka2IV+tjwQKwHB5SL9E8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HjnEy11nG+24YKVK5wTHmkDpR1JlzVXnaVqc4i1l4vBbWbK34oLdCtNIX2RJJMJ0to+IPFFF9XLLeq1X51ghhC1ID5zF3PMSgBMGcLhoe9i0XjojGRcisVVlla4bByllJxl4rlQExIjPsE61zfcaLsJkQxRLvnOprDnwPRZW24I= 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=eof4VMH8; arc=none smtp.client-ip=95.215.58.179 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="eof4VMH8" Message-ID: <97ea8f52-96c3-4109-92b7-cf2631a34e2d@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1730786540; 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=lmJNEv1TmoJq9gllep71bhmn3Ej/RQ01/Q8BC0veUJ0=; b=eof4VMH8ImSCRtUMAFGyQB4W0ssKELjeDNgjplivwUf7gwfTqdzgFokVIAiF+gtaGDpc49 +Jah2p1EeDIQpOdSTRDq22fjgMWMVpGpsgc2PjTxk/HgU+78+tq0bM4xlDDfzBFRgz7nSp 7j20Kd3aNo49bgDkFzAoXfs6I+HMQtw= Date: Mon, 4 Nov 2024 22:02:09 -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 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> <29e2658c-02c9-4ef1-a633-ee5017e72bc3@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 11/4/24 8:28 PM, Alexei Starovoitov wrote: > On Mon, Nov 4, 2024 at 7:50 PM Yonghong Song wrote: >> >> 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(). > What do you mean 'it's safe' ? > If you change bpf_prog_check_recur() to return false like this patch does > then kprobe progs will not have recursion protection > calling task_storage_get() helper. > In the context of this helper it means that kprobe progs have to use: > nobusy = bpf_task_storage_trylock(); > With this patch as-is there will be a deadlock in bpf_task_storage_lock() > when kprobe is using task storage. > So it looks broken to me. > > I also don't understand the point of this patch 2. > The patch 3 can still do: > > + switch (prog->type) { > + case BPF_PROG_TYPE_KPROBE: > + case BPF_PROG_TYPE_TRACEPOINT: > + case BPF_PROG_TYPE_PERF_EVENT: > + case BPF_PROG_TYPE_RAW_TRACEPOINT: > + return PRIV_STACK_ADAPTIVE; > + default: > + break; > + } > + > + if (!bpf_prog_check_recur(prog)) > + return NO_PRIV_STACK; > > which would mean that iter, lsm, struct_ops will not be allowed > to use priv stack. One example is e.g. a TC prog. Since bpf_prog_check_recur(prog) will return true (means supporting recursion), and private stack does not really support TC prog, the logic will become more complicated. I am totally okay with removing patch 2 and go back to my previous approach to explicitly list prog types supporting private stack. > > Unless struct_ops will explicit request priv stack via bool flag. > Then we will also add recursion protection in trampoline.