From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from plesk.hostmyservers.fr (plesk.hostmyservers.fr [45.145.164.37]) (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 A94BC3568F2; Fri, 5 Sep 2025 13:46:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.145.164.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757080007; cv=none; b=UtRlshZMxjlmxKH9n05eXvQ/ccQlXsr6Mzqbx1O2n/WZy/Wj7z0FmAiA65uOpMLlaczywJBM2LwSHk/6Qtbe31pbf6TuYoJBxATnGRve8HWShbfMN7dncPhzrntXTbgbm/CYsBfI3sbjUOr3PTMy9kwtnIo3NqY7ShOVlji55pA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757080007; c=relaxed/simple; bh=0Z+odll08XIx79p7xMrLB0QONIlzENyS3D9paA5KBFI=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=EaH8iySfw7qJV/OoVKKamG2Mpj6aBELNs5dXQF6oQE2dwYCaUKRL7uFRXk7YElP7o13pTvMRRnw2mlbY5AplruxWPigvBfQ7gItz4ot50WhvUHuealWFUIWKfVCDMFeJvRrxV5FZq8rTPyI2NIaN//UBU43SUJmBgZjfbXT1r8U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com; spf=pass smtp.mailfrom=arnaud-lcm.com; arc=none smtp.client-ip=45.145.164.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arnaud-lcm.com Received: from 7cf34ddaca59.ant.amazon.com (unknown [IPv6:2a01:e0a:3e8:c0d0:24ce:2523:e0d0:1c47]) by plesk.hostmyservers.fr (Postfix) with ESMTPSA id D1B61420C4; Fri, 5 Sep 2025 13:46:41 +0000 (UTC) Authentication-Results: Plesk; spf=pass (sender IP is 2a01:e0a:3e8:c0d0:24ce:2523:e0d0:1c47) smtp.mailfrom=contact@arnaud-lcm.com smtp.helo=7cf34ddaca59.ant.amazon.com Received-SPF: pass (Plesk: connection is authenticated) From: Arnaud lecomte To: alexei.starovoitov@gmail.com, yonghong.song@linux.dev, song@kernel.org Cc: andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, haoluo@google.com, john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org, linux-kernel@vger.kernel.org, martin.lau@linux.dev, sdf@fomichev.me, syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com, Arnaud Lecomte Subject: [PATCH bpf-next v8 1/3] bpf: refactor max_depth computation in bpf_get_stack() Date: Fri, 5 Sep 2025 15:46:25 +0200 Message-Id: <20250905134625.26531-1-contact@arnaud-lcm.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-PPP-Message-ID: <175708000245.25943.12706762412363530719@Plesk> X-PPP-Vhost: arnaud-lcm.com From: Arnaud Lecomte A new helper function stack_map_calculate_max_depth() that computes the max depth for a stackmap. Signed-off-by: Arnaud Lecomte Acked-by: Yonghong Song Acked-by: Song Liu --- Changes in v2: - Removed the checking 'map_size % map_elem_size' from stack_map_calculate_max_depth - Changed stack_map_calculate_max_depth params name to be more generic Changes in v3: - Changed map size param to size in max depth helper Changes in v4: - Fixed indentation in max depth helper for args Changes in v5: - Bound back trace_nr to num_elem in __bpf_get_stack - Make a copy of sysctl_perf_event_max_stack in stack_map_calculate_max_depth Changes in v6: - Restrained max_depth computation only when required - Additional cleanup from Song in __bpf_get_stack Changes in v7: - Removed additional cleanup from v6 Link to v7: https://lore.kernel.org/all/20250903233910.29431-1-contact@arnaud-lcm.com/ --- kernel/bpf/stackmap.c | 38 +++++++++++++++++++++++++++----------- 1 file changed, 27 insertions(+), 11 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 3615c06b7dfa..ed707bc07173 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -42,6 +42,28 @@ static inline int stack_map_data_size(struct bpf_map *map) sizeof(struct bpf_stack_build_id) : sizeof(u64); } +/** + * stack_map_calculate_max_depth - Calculate maximum allowed stack trace depth + * @size: Size of the buffer/map value in bytes + * @elem_size: Size of each stack trace element + * @flags: BPF stack trace flags (BPF_F_USER_STACK, BPF_F_USER_BUILD_ID, ...) + * + * Return: Maximum number of stack trace entries that can be safely stored + */ +static u32 stack_map_calculate_max_depth(u32 size, u32 elem_size, u64 flags) +{ + u32 skip = flags & BPF_F_SKIP_FIELD_MASK; + u32 max_depth; + u32 curr_sysctl_max_stack = READ_ONCE(sysctl_perf_event_max_stack); + + max_depth = size / elem_size; + max_depth += skip; + if (max_depth > curr_sysctl_max_stack) + return curr_sysctl_max_stack; + + return max_depth; +} + static int prealloc_elems_and_freelist(struct bpf_stack_map *smap) { u64 elem_size = sizeof(struct stack_map_bucket) + @@ -300,20 +322,17 @@ static long __bpf_get_stackid(struct bpf_map *map, BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, u64, flags) { - u32 max_depth = map->value_size / stack_map_data_size(map); - u32 skip = flags & BPF_F_SKIP_FIELD_MASK; + u32 elem_size = stack_map_data_size(map); bool user = flags & BPF_F_USER_STACK; struct perf_callchain_entry *trace; bool kernel = !user; + u32 max_depth; if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) return -EINVAL; - max_depth += skip; - if (max_depth > sysctl_perf_event_max_stack) - max_depth = sysctl_perf_event_max_stack; - + max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags); trace = get_perf_callchain(regs, 0, kernel, user, max_depth, false, false); @@ -406,8 +425,8 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, struct perf_callchain_entry *trace_in, void *buf, u32 size, u64 flags, bool may_fault) { - u32 trace_nr, copy_len, elem_size, num_elem, max_depth; bool user_build_id = flags & BPF_F_USER_BUILD_ID; + u32 trace_nr, copy_len, elem_size, max_depth; bool crosstask = task && task != current; u32 skip = flags & BPF_F_SKIP_FIELD_MASK; bool user = flags & BPF_F_USER_STACK; @@ -438,10 +457,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, goto clear; } - num_elem = size / elem_size; - max_depth = num_elem + skip; - if (sysctl_perf_event_max_stack < max_depth) - max_depth = sysctl_perf_event_max_stack; + max_depth = stack_map_calculate_max_depth(size, elem_size, flags); if (may_fault) rcu_read_lock(); /* need RCU for perf's callchain below */ -- 2.47.3