Re: [PATCH v9 02/12] kselftest: arm64: mangle_pstate_invalid_compat_toggle and common utils

From: Cristian Marussi <cristian.marussi@arm.com>
To: Suzuki K Poulose <suzuki.poulose@arm.com>,
	linux-kselftest@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, shuah@kernel.org
Cc: amit.kachhap@arm.com, andreyknvl@google.com, dave.martin@arm.com
Subject: Re: [PATCH v9 02/12] kselftest: arm64: mangle_pstate_invalid_compat_toggle and common utils
Date: Fri, 25 Oct 2019 10:56:39 +0100	[thread overview]
Message-ID: <d098f030-f3b7-82b6-8489-fa8985870237@arm.com> (raw)
In-Reply-To: <dde06d83-4c3b-0be4-db98-e740a1dd327e@arm.com>

On 24/10/2019 23:41, Suzuki K Poulose wrote:
> Hi Cristian,
> 
> On 10/09/2019 01:04 PM, Cristian Marussi wrote:
>> Add some arm64/signal specific boilerplate and utility code to help
>> further testcases' development.
>>
>> Introduce also one simple testcase mangle_pstate_invalid_compat_toggle
>> and some related helpers: it is a simple mangle testcase which messes
>> with the ucontext_t from within the signal handler, trying to toggle
>> PSTATE state bits to switch the system between 32bit/64bit execution
>> state. Expects SIGSEGV on test PASS.
>>
>> Reviewed-by: Dave Martin <Dave.Martin@arm.com>
>> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> 
> [...]
> 
>> +
>> +#define get_regval(regname, out)			\
>> +{							\
>> +	asm volatile("mrs %0, " __stringify(regname)	\
>> +	: "=r" (out)					\
>> +	:						\
>> +	: "memory");					\
>> +}
>> +
>> +/* Regs encoding and masks naming copied in from sysreg.h */
>> +#define SYS_ID_AA64MMFR1_EL1	S3_0_C0_C7_1	/* MRS Emulated */
>> +#define SYS_ID_AA64MMFR2_EL1	S3_0_C0_C7_2	/* MRS Emulated */
>> +#define ID_AA64MMFR1_PAN_SHIFT	20
>> +#define ID_AA64MMFR2_UAO_SHIFT	4
>> +
>> +/* Local Helpers */
>> +#define ID_AA64MMFR1_EL1_PAN_SUPPORTED(val) \
>> +	(!!((val) & (0xfUL << ID_AA64MMFR1_PAN_SHIFT)))
>> +#define ID_AA64MMFR2_EL1_UAO_SUPPORTED(val) \
>> +	(!!((val) & (0xfUL << ID_AA64MMFR2_UAO_SHIFT)))
>> +
>> +/*
>> + * Feature flags used in tdescr.feats_required to specify
>> + * any feature by the test
>> + */
>> +enum {
>> +	FSSBS_BIT,
>> +	FPAN_BIT,
>> +	FUAO_BIT,
>> +	FMAX_END
>> +};
>> +
>> +#define FEAT_SSBS		(1UL << FSSBS_BIT)
>> +#define FEAT_PAN		(1UL << FPAN_BIT)
>> +#define FEAT_UAO		(1UL << FUAO_BIT)
>> +
> 
> [...]
> 
>> +static int test_init(struct tdescr *td)
>> +{
>> +	td->minsigstksz = getauxval(AT_MINSIGSTKSZ);
>> +	if (!td->minsigstksz)
>> +		td->minsigstksz = MINSIGSTKSZ;
>> +	fprintf(stderr, "Detected MINSTKSIGSZ:%d\n", td->minsigstksz);
>> +
>> +	if (td->feats_required) {
>> +		td->feats_supported = 0;
>> +		/*
>> +		 * Checking for CPU required features using both the
>> +		 * auxval and the arm64 MRS Emulation to read sysregs.
>> +		 */
>> +		if (getauxval(AT_HWCAP) & HWCAP_SSBS)
>> +			td->feats_supported |= FEAT_SSBS;
>> +		if (getauxval(AT_HWCAP) & HWCAP_CPUID) {
>> +			uint64_t val = 0;
>> +
>> +			/* Uses MRS emulation to check capability */
>> +			get_regval(SYS_ID_AA64MMFR1_EL1, val);
>> +			if (ID_AA64MMFR1_EL1_PAN_SUPPORTED(val))
>> +				td->feats_supported |= FEAT_PAN;
>> +			/* Uses MRS emulation to check capability */
>> +			get_regval(SYS_ID_AA64MMFR2_EL1, val);
>> +			if (ID_AA64MMFR2_EL1_UAO_SUPPORTED(val))
>> +				td->feats_supported |= FEAT_UAO;
> 
> As discussed, these fields are never exposed to userspace via mrs. So
> you may as well drop these features.
> 

Yes I'm going to drop this code in v10 (which is also un-needed in fact by the current testcases)

Thanks

Cristian
> Cheers
> Suzuki
>