From: sashiko-bot@kernel.org
To: "Jiri Olsa" <jolsa@kernel.org>
Cc: bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next 5/9] bpf: Disable preemption in bpf_get_stackid
Date: Mon, 20 Jul 2026 09:04:10 +0000 [thread overview]
Message-ID: <20260720090411.61E931F00A3A@smtp.kernel.org> (raw)
In-Reply-To: <20260720085351.655075-6-jolsa@kernel.org>
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [High] Incomplete fix for preemption vulnerability in stack helpers (__bpf_get_stack)
--
--- Patch [5]: [PATCH bpf-next 5/9] bpf: Disable preemption in bpf_get_stackid ---
commit eb097d7647defa7379264dcdf95711bc573a419a
Author: Jiri Olsa <jolsa@kernel.org>
bpf: Disable preemption in bpf_get_stackid
This commit adds preempt_disable() and preempt_enable() around the
get_perf_callchain() call and trace buffer usage in bpf_get_stackid()
to prevent the per-CPU trace entries buffer from being corrupted if the
task is preempted.
Closes: https://lore.kernel.org/bpf/20260206090653.1336687-2-chen.dylane@linux.dev/
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index 83efd5892d907..a64b14ffd1e8e 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -625,30 +625,37 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
> struct perf_callchain_entry *trace;
> struct stackid stackid;
> bool kernel = !user;
> + int err = -EFAULT;
> u32 max_depth;
> - int err;
>
> 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 = stack_map_calculate_max_depth(map->value_size, elem_size, flags);
> +
> + preempt_disable();
> trace = get_perf_callchain(regs, kernel, user, max_depth,
> false, false, 0);
[Severity: High]
This isn't a bug introduced by this patch, but does __bpf_get_stack() also
need this preempt_disable() protection?
__bpf_get_stack() has a similar pattern where it calls get_perf_callchain()
or get_callchain_entry_for_task() and dereferences trace->ip via memcpy().
While it uses rcu_read_lock() when may_fault is true, on CONFIG_PREEMPT_RCU
kernels this does not prevent preemption.
Could a preempting task trigger another stack trace on the same CPU before
the memcpy() finishes, overwriting the per-CPU buffer in __bpf_get_stack()?
> if (unlikely(!trace))
> /* couldn't fetch the stack trace */
> - return -EFAULT;
> + goto out;
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260720085351.655075-1-jolsa@kernel.org?part=5
next prev parent reply other threads:[~2026-07-20 9:04 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 8:53 [PATCH bpf-next 0/9] bpf: Disable preemption in stack map code Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 1/9] bpf: Factor stackid_init function from __bpf_get_stackid Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 2/9] bpf: Factor stackid_fastpath " Jiri Olsa
2026-07-20 9:09 ` sashiko-bot
2026-07-20 20:31 ` Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 3/9] bpf: Factor stackid_new_bucket " Jiri Olsa
2026-07-20 9:01 ` sashiko-bot
2026-07-20 20:31 ` Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 4/9] bpf: Use stack id functions instead of __bpf_get_stackid Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 5/9] bpf: Disable preemption in bpf_get_stackid Jiri Olsa
2026-07-20 9:04 ` sashiko-bot [this message]
2026-07-20 20:31 ` Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 6/9] bpf: Factor callchain_store function from __bpf_get_stack Jiri Olsa
2026-07-20 9:07 ` sashiko-bot
2026-07-20 20:31 ` Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 7/9] bpf: Factor callchain_finalize " Jiri Olsa
2026-07-20 9:08 ` sashiko-bot
2026-07-20 20:31 ` Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 8/9] bpf: Remove trace_in argument " Jiri Olsa
2026-07-20 9:09 ` sashiko-bot
2026-07-20 20:31 ` Jiri Olsa
2026-07-20 8:53 ` [PATCH bpf-next 9/9] bpf: Disable preemption in __bpf_get_stack Jiri Olsa
2026-07-20 9:18 ` sashiko-bot
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