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(unknown [IPv6:2a02:8084:255b:aa00:acd6:d96f:40a0:aee]) by plesk.hostmyservers.fr (Postfix) with ESMTPSA id 72F1D4092E; Tue, 12 Aug 2025 19:30:45 +0000 (UTC) Authentication-Results: Plesk; spf=pass (sender IP is 2a02:8084:255b:aa00:acd6:d96f:40a0:aee) smtp.mailfrom=contact@arnaud-lcm.com smtp.helo=arnaudlcm-X570-UD.. Received-SPF: pass (Plesk: connection is authenticated) From: Arnaud Lecomte To: yonghong.song@linux.dev Cc: andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, contact@arnaud-lcm.com, 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, song@kernel.org, syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com Subject: [PATCH bpf-next v3 1/2] bpf: refactor max_depth computation in bpf_get_stack() Date: Tue, 12 Aug 2025 20:30:34 +0100 Message-ID: <20250812193034.18848-1-contact@arnaud-lcm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: 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: <175502704641.29886.4898775155046553663@Plesk> X-PPP-Vhost: arnaud-lcm.com A new helper function stack_map_calculate_max_depth() that computes the max depth for a stackmap. 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 Signed-off-by: Arnaud Lecomte --- kernel/bpf/stackmap.c | 30 ++++++++++++++++++++++++------ 1 file changed, 24 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 3615c06b7dfa..a267567e36dd 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -42,6 +42,27 @@ 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; + + max_depth = size / elem_size; + max_depth += skip; + if (max_depth > sysctl_perf_event_max_stack) + return sysctl_perf_event_max_stack; + + return max_depth; +} + static int prealloc_elems_and_freelist(struct bpf_stack_map *smap) { u64 elem_size = sizeof(struct stack_map_bucket) + @@ -406,7 +427,7 @@ 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; + u32 trace_nr, copy_len, elem_size, max_depth; bool user_build_id = flags & BPF_F_USER_BUILD_ID; bool crosstask = task && task != current; u32 skip = flags & BPF_F_SKIP_FIELD_MASK; @@ -438,10 +459,7 @@ 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 */ @@ -461,7 +479,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task, } trace_nr = trace->nr - skip; - trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem; + trace_nr = min(trace_nr, max_depth - skip); copy_len = trace_nr * elem_size; ips = trace->ip + skip; -- 2.43.0