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Subject: RE: [PATCH Part2 v6 06/49] x86/sev: Add helper functions for
 RMPUPDATE and PSMASH instruction
Thread-Topic: [PATCH Part2 v6 06/49] x86/sev: Add helper functions for
 RMPUPDATE and PSMASH instruction
Thread-Index: AQHYn4NDulHh/HmbIUq97K70l/FApa2bEhKQ
Date:   Tue, 2 Aug 2022 04:49:51 +0000
Message-ID: <SN6PR12MB27675C337244C0A6848167AA8E9D9@SN6PR12MB2767.namprd12.prod.outlook.com>
References: <cover.1655761627.git.ashish.kalra@amd.com>
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 <240cc182-4628-bef4-2b99-47331b0874f1@linux.ibm.com>
In-Reply-To: <240cc182-4628-bef4-2b99-47331b0874f1@linux.ibm.com>
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[AMD Official Use Only - General]

Hello Dov,

>> +int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid,=20
>> +bool immutable) {
>> +	struct rmpupdate val;
>> +
>> +	if (!pfn_valid(pfn))
>> +		return -EINVAL;
>> +

>Should we add more checks on the arguments?

>1. asid must be > 0
>2. gpa must be aligned according to 'level'
>3. gpa must be below the maximal address for the guest

Ok, yes it surely makes sense to add more checks on the arguments.

>"Note that the guest physical address space is limited according to CPUID =
Fn80000008_EAX and thus the GPAs used by the firmware in measurement calcul=
ation are equally limited. Hypervisors should not attempt to map pages outs=
ide of this limit."
>(-SNP ABI spec page 86, section 8.17 SNP_LAUNCH_UPDATE)


>But note that in patch 28 of this series we have:

>+		/* Transition the VMSA page to a firmware state. */
>+		ret =3D rmp_make_private(pfn, -1, PG_LEVEL_4K, sev->asid, true);

>That (u64)(-1) value for the gpa argument violates conditions 2 and 3 from=
 my list above.

>And indeed when calculating measurements we see that the GPA value for the=
 VMSA pages is 0x0000FFFF_FFFFF000, and not (u64)(-1). [1] [2]

>Instead of checks, we can mask the gpa argument so that rmpupdate will get=
 the correct value.  Not sure which approach is preferable.

Well, the firmware is anyway masking the gpa argument as you observe in the=
 launch digest, so probably we should do the same here too.

Thanks,
Ashish