Re: [PATCH] rcu: Fix kernel stack overflow caused by kprobe on rcu_irq_enter_check_tick()

From: Zheng Yejian
Date: Fri Dec 02 2022 - 04:54:56 EST



On 2022/11/22 03:57, Paul E. McKenney wrote:
On Sat, Nov 19, 2022 at 12:00:49PM +0800, Zheng Yejian wrote:
Register kprobe on __rcu_irq_enter_check_tick() can cause kernel stack
overflow [1]. This issue is first found in v5.10 and can be reproduced
by enabling CONFIG_NO_HZ_FULL and doing like:
# cd /sys/kernel/debug/tracing/
# echo 'p:mp1 __rcu_irq_enter_check_tick' >> kprobe_events
# echo 1 > events/kprobes/enable

So __rcu_irq_enter_check_tick() should not be kprobed, mark it as noinstr.

Good catch!

I am inclined to queue this, but noticed that one of its callers need
it to be noinstr but that the others do not.

Need noinstr:

o enter_from_kernel_mode() -> __enter_from_kernel_mode() ->
rcu_irq_enter_check_tick() -> __rcu_irq_enter_check_tick()

Doesn't need noinstr:

o ct_nmi_enter() -> rcu_irq_enter_check_tick() ->
__rcu_irq_enter_check_tick(), courtesy of the call to
instrumentation_begin() in ct_nmi_enter() that precedes the call
to rcu_irq_enter_check_tick().

o irqentry_enter() -> rcu_irq_enter_check_tick() ->
__rcu_irq_enter_check_tick(), courtesy of the call to
instrumentation_begin() in irqentry_enter() that precedes the
call to rcu_irq_enter_check_tick().

Is tagging __rcu_irq_enter_check_tick() with noinstr as
proposed in this patch the right thing to do, or should there
be calls to instrumentation_begin() and instrumentation_end() in
enter_from_kernel_mode()? Or something else entirely?

I have tried the calls to instrumentation_{begin,end}() in
enter_from_kernel_mode(), see [1]. But this problem can still be
reproduced, maybe more complete calltrace info [2] is needed for
analyzing.

Did I add the instrumentation_{begin,end}() in wrong place or is there other caller need noinstr?

[1]
diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 27369fa1c032..deed5a0941d3 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -49,7 +49,9 @@ static __always_inline void __enter_from_kernel_mode(struct pt_regs *regs)
}

lockdep_hardirqs_off(CALLER_ADDR0);
+ instrumentation_begin();
rcu_irq_enter_check_tick();
+ instrumentation_end();
trace_hardirqs_off_finish();
}


[2]
[ 48.921197] Call trace:
[ 48.921241] dump_backtrace+0xf8/0x108
[ 48.921358] show_stack+0x20/0x48
[ 48.921418] dump_stack_lvl+0x68/0x84
[ 48.921477] dump_stack+0x1c/0x38
[ 48.921530] panic+0x214/0x404
[ 48.921598] add_taint+0x0/0xf0
[ 48.921657] panic_bad_stack+0x144/0x160
[ 48.921715] handle_bad_stack+0x38/0x58
[ 48.921774] __bad_stack+0x78/0x7c
[ 48.921825] __rcu_irq_enter_check_tick+0x0/0x1b8
[ 48.921886] arm64_enter_el1_dbg.isra.0+0x14/0x20
[ 48.921949] el1_dbg+0x2c/0x90
[ 48.922001] el1h_64_sync_handler+0xcc/0xe8
[ 48.922061] el1h_64_sync+0x64/0x68
[ 48.922112] __rcu_irq_enter_check_tick+0x0/0x1b8
[...]
[ 48.938382] __rcu_irq_enter_check_tick+0x0/0x1b8
[ 48.938441] arm64_enter_el1_dbg.isra.0+0x14/0x20
[ 48.938500] el1_dbg+0x2c/0x90
[ 48.938549] el1h_64_sync_handler+0xcc/0xe8
[ 48.938607] el1h_64_sync+0x64/0x68
[ 48.938656] __rcu_irq_enter_check_tick+0x0/0x1b8
[ 48.938715] arm64_enter_el1_dbg.isra.0+0x14/0x20
[ 48.938778] el1_dbg+0x2c/0x90
[ 48.938829] el1h_64_sync_handler+0xcc/0xe8
[ 48.938887] el1h_64_sync+0x64/0x68
[ 48.938936] __rcu_irq_enter_check_tick+0x0/0x1b8
[ 48.938995] arm64_enter_el1_dbg.isra.0+0x14/0x20
[ 48.939054] el1_dbg+0x2c/0x90
[ 48.939105] el1h_64_sync_handler+0xcc/0xe8
[ 48.939164] el1h_64_sync+0x64/0x68
[ 48.939215] __rcu_irq_enter_check_tick+0x0/0x1b8
[ 48.939274] el1_interrupt+0x28/0x60
[ 48.939327] el1h_64_irq_handler+0x18/0x28
[ 48.939385] el1h_64_irq+0x64/0x68
[ 48.939434] __asan_load8+0x54/0xa8
[ 48.939500] __ftrace_set_clr_event_nolock+0x6c/0x198
[ 48.939563] __ftrace_set_clr_event+0x58/0x80
[ 48.939618] system_enable_write+0x144/0x178
[ 48.939673] vfs_write+0x174/0x738
[ 48.939734] ksys_write+0xd0/0x188
[ 48.939791] __arm64_sys_write+0x4c/0x60
[ 48.939851] invoke_syscall+0x64/0x180
[ 48.939921] el0_svc_common.constprop.0+0x84/0x160
[ 48.939996] do_el0_svc+0x48/0xf8
[ 48.940062] el0_svc+0x34/0xd0
[ 48.940114] el0t_64_sync_handler+0xb8/0xc0
[ 48.940173] el0t_64_sync+0x18c/0x190
[ 48.940872] SMP: stopping secondary CPUs
[ 48.942844] Kernel Offset: 0x2d9499c00000 from 0xffff800008000000
[ 48.942938] PHYS_OFFSET: 0xffffaa9840000000
[ 48.942999] CPU features: 0x00000,00d00080,0000421b
[ 48.943387] Memory Limit: none



Thoughts?

Sorry, I have no more idea :-(


Thanx, Paul

[1]
Insufficient stack space to handle exception!
Insufficient stack space to handle exception!
[...]
Kernel panic - not syncing: kernel stack overflow
CPU: 3 PID: 34 Comm: migration/3 Not tainted
6.1.0-rc5-00884-g84368d882b96 #2
Hardware name: linux,dummy-virt (DT)
Stopper: multi_cpu_stop+0x0/0x228 <- __stop_cpus.constprop.0+0xa4/0x100
Call trace:
dump_backtrace+0xf8/0x108
show_stack+0x20/0x48
dump_stack_lvl+0x68/0x84
dump_stack+0x1c/0x38
panic+0x214/0x404
add_taint+0x0/0xf0
panic_bad_stack+0x144/0x160
handle_bad_stack+0x38/0x58
__bad_stack+0x78/0x7c
el1h_64_sync_handler+0x4/0xe8
__rcu_irq_enter_check_tick+0x0/0x1b8
arm64_enter_el1_dbg.isra.0+0x14/0x20
el1_dbg+0x2c/0x90
el1h_64_sync_handler+0xcc/0xe8
el1h_64_sync+0x64/0x68
__rcu_irq_enter_check_tick+0x0/0x1b8
arm64_enter_el1_dbg.isra.0+0x14/0x20
el1_dbg+0x2c/0x90
el1h_64_sync_handler+0xcc/0xe8
el1h_64_sync+0x64/0x68
__rcu_irq_enter_check_tick+0x0/0x1b8
arm64_enter_el1_dbg.isra.0+0x14/0x20
el1_dbg+0x2c/0x90
el1h_64_sync_handler+0xcc/0xe8
el1h_64_sync+0x64/0x68
__rcu_irq_enter_check_tick+0x0/0x1b8
arm64_enter_el1_dbg.isra.0+0x14/0x20
el1_dbg+0x2c/0x90
el1h_64_sync_handler+0xcc/0xe8
el1h_64_sync+0x64/0x68
__rcu_irq_enter_check_tick+0x0/0x1b8
arm64_enter_el1_dbg.isra.0+0x14/0x20
el1_dbg+0x2c/0x90
el1h_64_sync_handler+0xcc/0xe8
el1h_64_sync+0x64/0x68
__rcu_irq_enter_check_tick+0x0/0x1b8
[...]

Cc: stable@xxxxxxxxxxxxxxx
Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()")
Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
---
kernel/rcu/tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 93416afebd59..68230f02cfb7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -631,7 +631,7 @@ void rcu_irq_exit_check_preempt(void)
* controlled environments, this function allows RCU to get what it
* needs without creating otherwise useless interruptions.
*/
-void __rcu_irq_enter_check_tick(void)
+noinstr void __rcu_irq_enter_check_tick(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
--
2.25.1

--
Best regards,
Zheng Yejian