harden_branch_predictor() call smp_processor_id() in preemptible
context, this would cause a bug messages.
The bug messages is as follows:
BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor0/17992
caller is harden_branch_predictor arch/arm/include/asm/system_misc.h:27 [inline]
caller is __do_user_fault+0x34/0x114 arch/arm/mm/fault.c:200
CPU: 1 PID: 17992 Comm: syz-executor0 Tainted: G O 4.4.176 #1
Hardware name: Hisilicon A9
[<c0114ae4>] (unwind_backtrace) from [<c010e6fc>] (show_stack+0x18/0x1c)
[<c010e6fc>] (show_stack) from [<c0379514>] (dump_stack+0xc8/0x118)
[<c0379514>] (dump_stack) from [<c039b5a0>] (check_preemption_disabled+0xf4/0x138)
[<c039b5a0>] (check_preemption_disabled) from [<c011abe4>] (__do_user_fault+0x34/0x114)
[<c011abe4>] (__do_user_fault) from [<c053b0d0>] (do_page_fault+0x3b4/0x3d8)
[<c053b0d0>] (do_page_fault) from [<c01013dc>] (do_DataAbort+0x58/0xf8)
[<c01013dc>] (do_DataAbort) from [<c053a880>] (__dabt_usr+0x40/0x60)
Reported-by: Jingwen Qiu <[email protected]>
Signed-off-by: Yongliang Gao <[email protected]>
Cc: <[email protected]>
---
arch/arm/include/asm/system_misc.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
index 66f6a3a..4a55cfb 100644
--- a/arch/arm/include/asm/system_misc.h
+++ b/arch/arm/include/asm/system_misc.h
@@ -22,9 +22,10 @@
static inline void harden_branch_predictor(void)
{
harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
- smp_processor_id());
+ get_cpu());
if (fn)
fn();
+ put_cpu();
}
#else
#define harden_branch_predictor() do { } while (0)
--
1.8.5.6
Hi Marc,
On 2019/6/3 18:17, Marc Zyngier wrote:
> On 27/05/2019 10:39, Yongliang Gao wrote:
>> harden_branch_predictor() call smp_processor_id() in preemptible
>> context, this would cause a bug messages.
>>
>> The bug messages is as follows:
>> BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor0/17992
>> caller is harden_branch_predictor arch/arm/include/asm/system_misc.h:27 [inline]
>> caller is __do_user_fault+0x34/0x114 arch/arm/mm/fault.c:200
>> CPU: 1 PID: 17992 Comm: syz-executor0 Tainted: G O 4.4.176 #1
>> Hardware name: Hisilicon A9
>> [<c0114ae4>] (unwind_backtrace) from [<c010e6fc>] (show_stack+0x18/0x1c)
>> [<c010e6fc>] (show_stack) from [<c0379514>] (dump_stack+0xc8/0x118)
>> [<c0379514>] (dump_stack) from [<c039b5a0>] (check_preemption_disabled+0xf4/0x138)
>> [<c039b5a0>] (check_preemption_disabled) from [<c011abe4>] (__do_user_fault+0x34/0x114)
>> [<c011abe4>] (__do_user_fault) from [<c053b0d0>] (do_page_fault+0x3b4/0x3d8)
>> [<c053b0d0>] (do_page_fault) from [<c01013dc>] (do_DataAbort+0x58/0xf8)
>> [<c01013dc>] (do_DataAbort) from [<c053a880>] (__dabt_usr+0x40/0x60)
>>
>> Reported-by: Jingwen Qiu <[email protected]>
>> Signed-off-by: Yongliang Gao <[email protected]>
>> Cc: <[email protected]>
>> ---
>> arch/arm/include/asm/system_misc.h | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
>> index 66f6a3a..4a55cfb 100644
>> --- a/arch/arm/include/asm/system_misc.h
>> +++ b/arch/arm/include/asm/system_misc.h
>> @@ -22,9 +22,10 @@
>> static inline void harden_branch_predictor(void)
>> {
>> harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
>> - smp_processor_id());
>> + get_cpu());
>> if (fn)
>> fn();
>> + put_cpu();
>> }
>> #else
>> #define harden_branch_predictor() do { } while (0)
>>
>
> This doesn't look like the right fix. If we're in a preemptible context,
> then we could invalidate the branch predictor on the wrong CPU.
Sorry, my bad, thanks a lot for the good catch.
>
> The right fix would be to move the call to a point where we haven't
> enabled preemption yet.
I took a look at the code, and find out that the caller of
harden_branch_predictor(), __do_user_fault(), is called by do_page_fault()
and do_bad_area(), those two function's context are both running with
preemption enabled, so I didn't find a good place to move the call,
could you please give some suggestion for my next step?
Best Regards
Yongliang
On 27/05/2019 10:39, Yongliang Gao wrote:
> harden_branch_predictor() call smp_processor_id() in preemptible
> context, this would cause a bug messages.
>
> The bug messages is as follows:
> BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor0/17992
> caller is harden_branch_predictor arch/arm/include/asm/system_misc.h:27 [inline]
> caller is __do_user_fault+0x34/0x114 arch/arm/mm/fault.c:200
> CPU: 1 PID: 17992 Comm: syz-executor0 Tainted: G O 4.4.176 #1
> Hardware name: Hisilicon A9
> [<c0114ae4>] (unwind_backtrace) from [<c010e6fc>] (show_stack+0x18/0x1c)
> [<c010e6fc>] (show_stack) from [<c0379514>] (dump_stack+0xc8/0x118)
> [<c0379514>] (dump_stack) from [<c039b5a0>] (check_preemption_disabled+0xf4/0x138)
> [<c039b5a0>] (check_preemption_disabled) from [<c011abe4>] (__do_user_fault+0x34/0x114)
> [<c011abe4>] (__do_user_fault) from [<c053b0d0>] (do_page_fault+0x3b4/0x3d8)
> [<c053b0d0>] (do_page_fault) from [<c01013dc>] (do_DataAbort+0x58/0xf8)
> [<c01013dc>] (do_DataAbort) from [<c053a880>] (__dabt_usr+0x40/0x60)
>
> Reported-by: Jingwen Qiu <[email protected]>
> Signed-off-by: Yongliang Gao <[email protected]>
> Cc: <[email protected]>
> ---
> arch/arm/include/asm/system_misc.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
> index 66f6a3a..4a55cfb 100644
> --- a/arch/arm/include/asm/system_misc.h
> +++ b/arch/arm/include/asm/system_misc.h
> @@ -22,9 +22,10 @@
> static inline void harden_branch_predictor(void)
> {
> harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
> - smp_processor_id());
> + get_cpu());
> if (fn)
> fn();
> + put_cpu();
> }
> #else
> #define harden_branch_predictor() do { } while (0)
>
This doesn't look like the right fix. If we're in a preemptible context,
then we could invalidate the branch predictor on the wrong CPU.
The right fix would be to move the call to a point where we haven't
enabled preemption yet.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
On 03/06/2019 15:44, gaoyongliang wrote:
> Hi Marc,
>
> On 2019/6/3 18:17, Marc Zyngier wrote:
>> On 27/05/2019 10:39, Yongliang Gao wrote:
>>> harden_branch_predictor() call smp_processor_id() in preemptible
>>> context, this would cause a bug messages.
>>>
>>> The bug messages is as follows:
>>> BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor0/17992
>>> caller is harden_branch_predictor arch/arm/include/asm/system_misc.h:27 [inline]
>>> caller is __do_user_fault+0x34/0x114 arch/arm/mm/fault.c:200
>>> CPU: 1 PID: 17992 Comm: syz-executor0 Tainted: G O 4.4.176 #1
>>> Hardware name: Hisilicon A9
>>> [<c0114ae4>] (unwind_backtrace) from [<c010e6fc>] (show_stack+0x18/0x1c)
>>> [<c010e6fc>] (show_stack) from [<c0379514>] (dump_stack+0xc8/0x118)
>>> [<c0379514>] (dump_stack) from [<c039b5a0>] (check_preemption_disabled+0xf4/0x138)
>>> [<c039b5a0>] (check_preemption_disabled) from [<c011abe4>] (__do_user_fault+0x34/0x114)
>>> [<c011abe4>] (__do_user_fault) from [<c053b0d0>] (do_page_fault+0x3b4/0x3d8)
>>> [<c053b0d0>] (do_page_fault) from [<c01013dc>] (do_DataAbort+0x58/0xf8)
>>> [<c01013dc>] (do_DataAbort) from [<c053a880>] (__dabt_usr+0x40/0x60)
>>>
>>> Reported-by: Jingwen Qiu <[email protected]>
>>> Signed-off-by: Yongliang Gao <[email protected]>
>>> Cc: <[email protected]>
>>> ---
>>> arch/arm/include/asm/system_misc.h | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
>>> index 66f6a3a..4a55cfb 100644
>>> --- a/arch/arm/include/asm/system_misc.h
>>> +++ b/arch/arm/include/asm/system_misc.h
>>> @@ -22,9 +22,10 @@
>>> static inline void harden_branch_predictor(void)
>>> {
>>> harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn,
>>> - smp_processor_id());
>>> + get_cpu());
>>> if (fn)
>>> fn();
>>> + put_cpu();
>>> }
>>> #else
>>> #define harden_branch_predictor() do { } while (0)
>>>
>>
>> This doesn't look like the right fix. If we're in a preemptible context,
>> then we could invalidate the branch predictor on the wrong CPU.
>
> Sorry, my bad, thanks a lot for the good catch.
>
>>
>> The right fix would be to move the call to a point where we haven't
>> enabled preemption yet.
>
> I took a look at the code, and find out that the caller of
> harden_branch_predictor(), __do_user_fault(), is called by do_page_fault()
> and do_bad_area(), those two function's context are both running with
> preemption enabled, so I didn't find a good place to move the call,
> could you please give some suggestion for my next step?
Since we land here from do_page_fault, it seems natural to move the
invalidation up there, probably before we re-enable interrupts.
Thanks,
M.
--
Jazz is not dead. It just smells funny...