Re: [PATCH RESEND 2/2] x86/mm: Randomize va with generic arch_pick_mmap_layout()

[Xiongwei Song]

> On Sep 21, 2021, at 10:41 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> On Tue, Sep 21, 2021 at 10:34:14PM +0800, sxwjean@xxxxxx wrote:
>> diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
>> index 7516e4199b3c..c697e377644d 100644
>> --- a/arch/x86/include/asm/compat.h
>> +++ b/arch/x86/include/asm/compat.h
>> @@ -151,6 +151,11 @@ struct compat_shmid64_ds {
>> 	compat_ulong_t __unused5;
>> };
>> 
>> +static inline int is_compat_task(void)
>> +{
>> +	return IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT);
>> +}
>> +
> 
> This is still fundamentally broken for x86. x86 doesn't have compat
> tasks, the granularity is at syscall at best.

Hi Peter,

Thank you for pointing this out. I understand now a 64bit task can call a 32bit syscall. 
Here we should use in_compat_syscall() to check if the kernel is in compat mode, right?

Regards,
Xiongwei