Re: [PATCH v3 01/16] arm64: cpufeature: add pointer auth meta-capabilities

From: Suzuki Kuruppassery Poulose <suzuki.poulose@arm.com>
To: Catalin Marinas <Catalin.Marinas@arm.com>,
	Amit Kachhap <Amit.Kachhap@arm.com>
Cc: Mark Rutland <Mark.Rutland@arm.com>,
	Kees Cook <keescook@chromium.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Richard Henderson <richard.henderson@linaro.org>,
	Kristina Martsenko <Kristina.Martsenko@arm.com>,
	James Morse <James.Morse@arm.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Mark Brown <Mark.Brown@arm.com>,
	Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
	Will Deacon <will@kernel.org>,
	Dave P Martin <Dave.Martin@arm.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3 01/16] arm64: cpufeature: add pointer auth meta-capabilities
Date: Wed, 15 Jan 2020 13:52:24 +0000	[thread overview]
Message-ID: <4aac989f-3d9e-53e0-e2c9-1aa163e6baa0@arm.com> (raw)
In-Reply-To: <20200115122657.GB3429@arrakis.emea.arm.com>

On 15/01/2020 12:26, Catalin Marinas wrote:
> On Mon, Dec 16, 2019 at 02:17:03PM +0530, Amit Daniel Kachhap wrote:
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index 04cf64e..cf42c46 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -1249,6 +1249,20 @@ static void cpu_enable_address_auth(struct arm64_cpu_capabilities const *cap)
>>   	sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ENIA | SCTLR_ELx_ENIB |
>>   				       SCTLR_ELx_ENDA | SCTLR_ELx_ENDB);
>>   }
>> +
>> +static bool has_address_auth(const struct arm64_cpu_capabilities *entry,
>> +			     int __unused)
>> +{
>> +	return cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH_ARCH) ||
>> +	       cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH_IMP_DEF);
>> +}
>> +
>> +static bool has_generic_auth(const struct arm64_cpu_capabilities *entry,
>> +			     int __unused)
>> +{
>> +	return cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH_ARCH) ||
>> +	       cpus_have_const_cap(ARM64_HAS_GENERIC_AUTH_IMP_DEF);
>> +}
> 
> Do these rely on the order in which the entries are listed in the
> arm64_features[] array? It looks like we do the same for PAN_NOT_UAO but
> that's pretty fragile.

Yes, it surely depends on the order in which they are listed.

> 
> I'd prefer if we invoked the
> cpu_hwcaps_ptrs[ARM64_HAS_ADDRESS_AUTH]->matches() directly here, maybe

Yes, calling the matches(cap, SYSTEM_SCOPE), that should work and is 
much better.

> hidden behind a helper (I couldn't find one at a quick look).
> 

There are no helpers for this operation to  do it on a SYSTEM_SCOPE
and this is only needed for caps dependent on the other caps.

May be we could hide the conversion of the number to "cap" as:

static inline struct arm64_cpu_capabilities *cpu_cap_from_number(int n)
{
	if (n < ARM64_NCAPS)
		return cpu_hwcaps_ptr[n];
	return NULL;
}

And use this for "this_cpu_has_cap()" too.

Suzuki

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