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

Kristina Martsenko
2019-02-13T17:32:37Z

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.

>
> ('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
>