Re: [PATCH v5 1/5] arm64: Add utilities to save restore pointer authentication keys

Amit Daniel Kachhap
2019-02-14T10:53:53Z

Hi,

On 2/13/19 11:02 PM, Kristina Martsenko wrote:
> On 31/01/2019 16:20, James Morse wrote:
>> Hi Amit,
>>
>> On 28/01/2019 06:58, Amit Daniel Kachhap wrote:
>>> The keys can be switched either inside an assembly or such
>>> functions which do not have pointer authentication checks, so a GCC
>>> attribute is added to enable it.
>>>
>>> A function ptrauth_keys_store is added which is similar to existing
>>> function ptrauth_keys_switch but saves the key values in memory.
>>> This may be useful for save/restore scenarios when CPU changes
>>> privilege levels, suspend/resume etc.
>>
>>
>>> diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
>>> index 15d4951..98441ce 100644
>>> --- a/arch/arm64/include/asm/pointer_auth.h
>>> +++ b/arch/arm64/include/asm/pointer_auth.h
>>> @@ -11,6 +11,13 @@
>>>
>>> #ifdef CONFIG_ARM64_PTR_AUTH
>>> /*
>>> + * Compile the function without pointer authentication instructions. This
>>> + * allows pointer authentication to be enabled/disabled within the function
>>> + * (but leaves the function unprotected by pointer authentication).
>>> + */
>>> +#define __no_ptrauth __attribute__((target("sign-return-address=none")))
>>
>> The documentation[0] for this says 'none' is the default. Will this only
>> take-effect once the kernel supports pointer-auth for the host? (Is this just
>> documentation until then?)
>
> Yes, I don't think this should be in this series, since we're not
> building the kernel with pointer auth yet.
I added it to stress on some functions which should be pointer
authentication safe. Yes this can be dropped and a small comment may
also do.

//Amit D
>
>>
>> ('noptrauth' would fit with 'notrace' slightly better)
>
> (But worse with e.g. __noreturn, __notrace_funcgraph, __init,
> __always_inline, __exception. Not sure what the pattern is. Would
> __noptrauth be better?)
>
> Thanks,
> Kristina
>
>>
>> [0]
>> https://gcc.gnu.org/onlinedocs/gcc/AArch64-Function-Attributes.html#AArch64-Function-Attributes
>>
>