[PATCH v3 3/3] arm64: kprobe: disable probe of fault prone ptrauth instruction

[Amit Daniel Kachhap]

On 6/22/20 8:10 PM, Dave Martin wrote:
> On Thu, Jun 18, 2020 at 10:40:29AM +0530, Amit Daniel Kachhap wrote:
>> This patch disables the probing of authenticate ptrauth instruction (AUT*)
>> which falls under the hint instructions region. This is done to disallow
>> probe of authenticate instruction which may lead to ptrauth faults with the
>> addition of Armv8.6 enhanced ptrauth features.
>>
>> The corresponding append pac ptrauth instruction (PAC*) is not disabled
>> and they can still be probed.
> 
> Seems sensible.  Might be worth noting here why we think this is
> reasonable: AUT* instructions make no sense at function entry points,
> so most realistic probes would be unaffected by this change.

Ok sure it make sense to add these details. Thanks for pointing this out.

> 
> Since stepping on older hardware is safe, we could make this conditional
> based on cpufeatures.  It hardly seems worth it, though.

Yes agreed.

> 
>> Signed-off-by: Amit Daniel Kachhap <amit.kachhap at arm.com>
>> ---

>>   
>>   		/*
>> -		 * The HINT instruction is is problematic when single-stepping,
>> +		 * The HINT instruction is problematic when single-stepping,
> 
> Nit: doesn't matter too much, but ideally this should be a separate
> patch (or just don't bother).

ok.

> 
> Cheers
> ---Dave
>