RE: [PATCH] ftrace: remove KASAN poison in ftrace_ops_test()

[Zhang Zhizhou(åææ)]

> -----Original Message-----
> From: Mark Rutland [mailto:mark.rutland@xxxxxxx]
> Sent: Monday, November 12, 2018 1:32 AM
> To: Zhang Zhizhou(åææ) <zhizhouzhang@xxxxxxxxxxxx>
> Cc: rostedt@xxxxxxxxxxx; mingo@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; zhizhouzh@xxxxxxxxx
> Subject: Re: [PATCH] ftrace: remove KASAN poison in ftrace_ops_test()
> 
> On Sun, Nov 11, 2018 at 11:10:17PM +0800, Zhizhou Zhang wrote:
> > ftrace_ops_test() passed local varible parameter to
> > hash_contains_ip(), which could result KASAN stack-out-of-bounds
> warning.
> >
> > Signed-off-by: Zhizhou Zhang <zhizhouzhang@xxxxxxxxxxxx>
> > ---
> >  kernel/trace/ftrace.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index
> > f536f60..6e11f90 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -1522,6 +1522,8 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned
> long ip, void *regs)
> >  	rcu_assign_pointer(hash.filter_hash, ops->func_hash->filter_hash);
> >  	rcu_assign_pointer(hash.notrace_hash, ops->func_hash-
> >notrace_hash);
> >
> > +	kasan_unpoison_task_stack(current);
> 
> This is extremely heavy-handed, and will mask legitimate stack-out-of-
> bounds errors.
> 
Yes. I tried to find ways to mark this function no need to poison, but failed. My first thought was just make this function not poison its stack.

> Passing a stack-local variable by reference *should not* result in KASAN
> warnings unless KASAN itself is broken. Can you please give an example
> report when this occurs?
> 
Please excuse my lack of knowledge. Did you mean if a function passing a stack-local variable as parameter to another function, the compiler won't poison the stack-local variable?
The KASAN report is based on 4.4.145, I'm not sure for the latest kernel:

c3 0 (swapper/3) ==================================================================
c3 0 (swapper/3) BUG: KASAN: stack-out-of-bounds in hash_contains_ip.isra.4+0x44/0xd0
c3 0 (swapper/3) Read of size 8 at addr ffffffc0d204bc20 by task swapper/3/0
c3 0 (swapper/3) 
c3 0 (swapper/3) CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.4.145+ #168
c3 0 (swapper/3) Hardware name: ASR AQUILAC EVB (DT)
c3 0 (swapper/3) Call trace:
c3 0 (swapper/3) [<ffffff9008091a50>] dump_backtrace+0x0/0x418
c3 0 (swapper/3) [<ffffff9008091e90>] show_stack+0x28/0x38
c3 0 (swapper/3) [<ffffff90086253a4>] dump_stack+0xe8/0x13c
c3 0 (swapper/3) [<ffffff900831c15c>] print_address_description+0x8c/0x2b0
c3 0 (swapper/3) [<ffffff900831c688>] kasan_report+0x210/0x330
c3 0 (swapper/3) [<ffffff900831aba4>] __asan_load8+0x84/0x98
c3 0 (swapper/3) [<ffffff900821a694>] hash_contains_ip.isra.4+0x44/0xd0
c3 0 (swapper/3) [<ffffff900821a7c8>] ftrace_ops_test.isra.5+0xa8/0xe0
c3 0 (swapper/3) [<ffffff90082239cc>] ftrace_ops_no_ops+0xdc/0x218
c3 0 (swapper/3) [<ffffff90080a1d0c>] ftrace_graph_call+0x0/0x14
c3 0 (swapper/3) [<ffffff900809afbc>] scale_cpu_capacity+0x24/0x70
c3 0 (swapper/3) [<ffffff900813ada0>] sync_entity_load_avg+0xb0/0x4c0
c3 0 (swapper/3) [<ffffff900813b1dc>] remove_entity_load_avg+0x2c/0x80
c3 0 (swapper/3) [<ffffff900813b250>] task_dead_fair+0x20/0x30
c3 0 (swapper/3) [<ffffff900811169c>] finish_task_switch+0x1f4/0x2a0
c3 0 (swapper/3) [<ffffff90092deb94>] __schedule+0x4cc/0xe80
c3 0 (swapper/3) [<ffffff90092df820>] schedule+0x70/0x110
c3 0 (swapper/3) [<ffffff90092dfbdc>] schedule_preempt_disabled+0x24/0x70
c3 0 (swapper/3) [<ffffff9008151dc8>] cpu_startup_entry+0x198/0x538
c3 0 (swapper/3) [<ffffff9008099f38>] secondary_start_kernel+0x258/0x2f0
c3 0 (swapper/3) [<00000001032e803c>] 0x1032e803c
c3 0 (swapper/3) 
c3 0 (swapper/3) The buggy address belongs to the page:
c3 0 (swapper/3) page:ffffffbdc34812c0 count:0 mapcount:0 mapping:          (null) index:0x0
c3 0 (swapper/3) flags: 0x0()
c3 0 (swapper/3) page dumped because: kasan: bad access detected
c3 0 (swapper/3) 
c3 0 (swapper/3) Memory state around the buggy address:
c3 0 (swapper/3)  ffffffc0d204bb00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c3 0 (swapper/3)  ffffffc0d204bb80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
c3 0 (swapper/3) >ffffffc0d204bc00: f1 f1 f1 f1 f3 f3 f3 f3 00 00 00 00 00 00 00 00
c3 0 (swapper/3)                                ^
c3 0 (swapper/3)  ffffffc0d204bc80: 00 00 00 00 00 00 f2 f2 00 00 00 00 00 00 00 00
c3 0 (swapper/3)  ffffffc0d204bd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c3 0 (swapper/3) ==================================================================
c3 1 (init) init: Untracked pid 3103 killed by signal 14
c4 972 (syz-executor) asr-wdt d4080000.watchdog: feed asr_wdt(soc_wdt).
c5 431 (kworker/u16:8) C0_DFC: Time 117510987492 (1248 -> 1600);
c5 431 (kworker/u16:8) C0_DFC: Time 117582358799 (1600 -> 1248);
c5 431 (kworker/u16:8) C1_DFC: Time 51133656270 (1900 -> 1248);
c5 431 (kworker/u16:8) C1_DFC: Time 51133864462 (1248 -> 1600);
c5 431 (kworker/u16:8) DDR_DFC: Time 0 (0 -> 0);
c5 431 (kworker/u16:8) DDR_DFC: Time 0 (0 -> 0);
c5 431 (kworker/u16:8) CLK:      GPU(312000000, 0);VPU(832000000, 0);ISP(312000000, 0);
c5 431 (kworker/u16:8) DVC:      clst0(11); clst1(11); m2(11); peri(1); d1p(1);
c5 431 (kworker/u16:8) Temp:     cpu(82000); gpu(64000); ddr(68000); local(64000); battery(0); pmic(0)
c5 431 (kworker/u16:8) Battery:  soc(57648); i_battery(-941556);
c5 431 (kworker/u16:8) 88pm88x-battery 88pm88x-battery: l=80% v=3957mV t0=25C t1=0C c=-941mA st=UNKNOWN ocv=0

> Which compiler are you using?
> 
I'm using gcc 7.1.0: aarch64-linux-gnu-gcc (GCC) 7.1.0.

> Thanks,
> Mark.
> 
> > +
> >  	if (hash_contains_ip(ip, &hash))
> >  		ret = 1;
> >  	else
> > --
> > 2.7.4
> >