linux-kernel - [PATCH] x86: profiling: Set prof_cpu

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Date:   Fri, 24 Feb 2023 16:49:45 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <chenzhongjin@...wei.com>, <akpm@...ux-foudation.org>,
        <wuchi.zero@...il.com>, <ben-linux@...ff.org>,
        <rusty@...tcorp.com.au>
Subject: [PATCH] x86: profiling: Set prof_cpu_mask to NULL after free

KASAN reported a UAF problem in profile_tick():

  BUG: KASAN: use-after-free in profile_tick+0x5c/0x80
  Read of size 8 at addr ffff888100928aa0 by task bash/1108

  CPU: 2 PID: 1108 Comm: bash Not tainted 5.10.0+ #72
  Call Trace:
   <IRQ>
   dump_stack+0x93/0xc5
   print_address_description.constprop.0+0x1c/0x3c0
   kasan_report.cold+0x37/0x74
   check_memory_region+0x161/0x1c0
   profile_tick+0x5c/0x80
   tick_sched_timer+0xcd/0x100
   __hrtimer_run_queues+0x23e/0x480
   hrtimer_interrupt+0x1c2/0x440
   asm_call_irq_on_stack+0xf/0x20
   </IRQ>
  ...

It is beacause in profiling_store(), profile_init() is possible to fail
and free prof_cpu_mask. However prof_cpu_mask is not set to NULL and
cpumask_available(prof_cpu_mask) will return true in profile_tick().
Then cpumask_test_cpu() will dereference prof_cpu_mask and trigger the
KASAN warning.

There is no interface to disable profile_tick() even though profile_init()
has been already failed. So just set prof_cpu_mask to NULL when free it.
Then accessing to prof_cpu_mask can be rejected by prof_buffer or
cpumask_available().

Fixes: c309b917cab5 ("cpumask: convert kernel/profile.c")
Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
---
 kernel/profile.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/profile.c b/kernel/profile.c
index 8a77769bc4b4..d60f9634fb2a 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -133,6 +133,7 @@ int __ref profile_init(void)
 		return 0;

 	free_cpumask_var(prof_cpu_mask);
+	prof_cpu_mask = NULL;
 	return -ENOMEM;
 }

@@ -334,7 +335,7 @@ void profile_tick(int type)
 {
 	struct pt_regs *regs = get_irq_regs();

-	if (!user_mode(regs) && cpumask_available(prof_cpu_mask) &&
+	if (!user_mode(regs) && prof_buffer && cpumask_available(prof_cpu_mask) &&
 	    cpumask_test_cpu(smp_processor_id(), prof_cpu_mask))
 		profile_hit(type, (void *)profile_pc(regs));
 }
-- 
2.17.1