linux-kernel - [PATCH v4 0/3] sched_ext: Harden scx_bpf_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250811212150.85759-1-christian.loehle@arm.com>
Date: Mon, 11 Aug 2025 22:21:47 +0100
From: Christian Loehle <christian.loehle@....com>
To: tj@...nel.org,
	arighi@...dia.com,
	void@...ifault.com
Cc: linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	changwoo@...lia.com,
	hodgesd@...a.com,
	mingo@...hat.com,
	peterz@...radead.org,
	jake@...lion.co.uk,
	Christian Loehle <christian.loehle@....com>
Subject: [PATCH v4 0/3] sched_ext: Harden scx_bpf_cpu_rq()

scx_bpf_cpu_rq() currently allows accessing struct rq fields without
holding the associated rq.
It is being used by scx_cosmos, scx_flash, scx_lavd, scx_layered, and
scx_tickless. Fortunately it is only ever used to fetch rq->curr.
So provide an alternative scx_bpf_task_acquire_remote_curr() that
doesn't expose struct rq and provide a hardened scx_bpf_cpu_rq_locked()
by ensuring we hold the rq lock.
Add a deprecation warning to scx_bpf_cpu_rq_locked() that mentions the
two alternatives.

This also simplifies scx code from:

rq = scx_bpf_cpu_rq(cpu);
if (!rq)
	return;
p = rq->curr
if (!p)
	return;
/* ... Do something with p */

into:

p = scx_bpf_task_acquire_remote_curr(cpu);
if (!p)
	return;
/* ... Do something with p */
bpf_task_release(p);


v3:
https://lore.kernel.org/lkml/20250805111036.130121-1-christian.loehle@arm.com/
Don't change scx_bpf_cpu_rq() do not break BPF schedulers without the
grace period. Just add the deprecation warning and do the hardening in
the new scx_bpf_cpu_rq_locked(). (Andrea, Tejun, Jake)
v2:
https://lore.kernel.org/lkml/20250804112743.711816-1-christian.loehle@arm.com/
- Open-code bpf_task_acquire() to avoid the forward declaration (Andrea)
- Rename scx_bpf_task_acquire_remote_curr() to make it more explicit it
behaves like bpf_task_acquire()
- Dis
v1:
https://lore.kernel.org/lkml/20250801141741.355059-1-christian.loehle@arm.com/
- scx_bpf_cpu_rq() now errors when a not locked rq is requested. (Andrea)
- scx_bpf_remote_curr() calls bpf_task_acquire() which BPF user needs to
release. (Andrea)
Christian Loehle (3):
  sched_ext: Introduce scx_bpf_cpu_rq_locked()
  sched_ext: Provide scx_bpf_task_acquire_remote_curr()
  sched_ext: deprecation warn for scx_bpf_cpu_rq()

 kernel/sched/ext.c                       | 49 ++++++++++++++++++++++++
 tools/sched_ext/include/scx/common.bpf.h |  2 +
 2 files changed, 51 insertions(+)

-- 
2.34.1