linux-kernel - Re: [Bug] "BUG: soft lockup in perf_event

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Message-ID: <jnrnpz2sms365aleeowcwisbefiekvkhbd6s5x42z7wuqnfxcy@dr6tkjizp3v5>
Date: Wed, 21 May 2025 08:57:11 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: John <john.cs.hey@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	linux-kernel@...r.kernel.org, Paul Moore <paul@...l-moore.com>, 
	Stephen Smalley <stephen.smalley.work@...il.com>
Subject: Re: [Bug] "BUG: soft lockup in perf_event_open" in Linux kernel v6.14

On Wed, May 21, 2025 at 09:49:41PM +0800, John wrote:
> Dear Linux Kernel Maintainers,
> 
> I hope this message finds you well.
> 
> I am writing to report a potential vulnerability I encountered during
> testing of the Linux Kernel version v6.14.
> 
> Git Commit: 38fec10eb60d687e30c8c6b5420d86e8149f7557 (tag: v6.14)
> 
> Bug Location: 0010:orc_find arch/x86/kernel/unwind_orc.c:217
> 
> Bug report: https://pastebin.com/QzuTF9kT
> 
> Complete log: https://pastebin.com/XjZYbiCH
> 
> Entire kernel config: https://pastebin.com/MRWGr3nv
> 
> Root Cause Analysis:
> 
> A soft lockup occurred on CPU#0 in the unwind_next_frame() function
> during stack unwinding triggered by arch_stack_walk().
> This was called in the middle of __kasan_slab_free() as part of RCU
> reclamation path (rcu_do_batch()), likely triggered by a SLAB object
> free in SELinux's avc_reclaim_node().
> The system was under heavy AVC pressure due to continuous audit and
> avc_has_perm() calls (e.g., from selinux_perf_event_open), leading to
> repeated avc_node allocations and reclamations under spinlocks.

I'm out of the office but I couldn't help myself glancing at it.

It looks like a deadlock in the selinux code.  Two of the CPUs are
waiting for a spinlock in avc_reclaim_node().  A third CPU is running in
avc code (currently context_struct_compute_av).

Adding a few selinux folks.

-- 
Josh