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SubjectRe: [PATCH 2/3] x86/tme: Detect if TME and MKTME is activated by BIOS
On Wed, Feb 07, 2018 at 05:34:10PM +1300, Kai Huang wrote:
> On Wed, 2018-01-31 at 12:15 +0300, Kirill A. Shutemov wrote:
> > IA32_TME_ACTIVATE MSR (0x982) can be used to check if BIOS has
> > enabled
> > TME and MKTME. It includes which encryption policy/algorithm is
> > selected
> > for TME or available for MKTME. For MKTME, the MSR also enumerates
> > how
> > many KeyIDs are available.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> > arch/x86/kernel/cpu/intel.c | 83
> > +++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 83 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/intel.c
> > b/arch/x86/kernel/cpu/intel.c
> > index 6936d14d4c77..5b95fa484837 100644
> > --- a/arch/x86/kernel/cpu/intel.c
> > +++ b/arch/x86/kernel/cpu/intel.c
> > @@ -517,6 +517,86 @@ static void detect_vmx_virtcap(struct
> > cpuinfo_x86 *c)
> > }
> > }
> >
> > +#define MSR_IA32_TME_ACTIVATE 0x982
>
> Should this MSR go into msr-index.h?

No. Comment from msr-index.h:

* Do not add new entries to this file unless the definitions are shared
* between multiple compilation units.

> > +
> > +#define TME_ACTIVATE_LOCKED(x) (x & 0x1)
> > +#define TME_ACTIVATE_ENABLED(x) (x & 0x2)
> > +
> > +#define TME_ACTIVATE_POLICY(x) ((x >> 4) & 0xf)
> > /* Bits 7:4 */
> > +#define TME_ACTIVATE_POLICY_AES_XTS 0
> > +
> > +#define TME_ACTIVATE_KEYID_BITS(x) ((x >> 32) & 0xf) /
> > * Bits 35:32 */
> > +
> > +#define TME_ACTIVATE_CRYPTO_ALGS(x) ((x >> 48) & 0xffff)
> > /* Bits 63:48 */
> > +#define TME_ACTIVATE_CRYPTO_AES_XTS 1
> > +
> > +#define MKTME_ENABLED 0
> > +#define MKTME_DISABLED 1
> > +#define MKTME_UNINITIALIZED 2
> > +static int mktme_status = MKTME_UNINITIALIZED;
> > +
> > +static void detect_tme(struct cpuinfo_x86 *c)
> > +{
> > + u64 tme_activate, tme_policy, tme_crypto_algs;
> > + int keyid_bits = 0, nr_keyids = 0;
> > + static u64 tme_activate_cpu0 = 0;
> > +
> > + rdmsrl(MSR_IA32_TME_ACTIVATE, tme_activate);
> > +
> > + if (mktme_status != MKTME_UNINITIALIZED) {
> > + /* Broken BIOS? */
> > + if (tme_activate != tme_activate_cpu0) {
> > + pr_err_once("TME: configuation is
> > inconsistent between CPUs\n");
> > + mktme_status = MKTME_DISABLED;
> > + }
> > + goto out;
>
> Why goto out here? If something goes wrong, I think it is pointless to
> read keyID bits staff? IMHO if something goes wrong, you should set
> mktme_status to disabled, and clear tme_activate_cpu0?

We still have to mask out keyid bits from x86_phys_bits if CPU has TME
enabled. But yeah, as you pointed below, I need to check that it actually
locked and enabled.

> > + }
> > +
> > + tme_activate_cpu0 = tme_activate;
> > +
> > + if (!TME_ACTIVATE_LOCKED(tme_activate) ||
> > !TME_ACTIVATE_ENABLED(tme_activate)) {
> > + pr_info("TME: not enabled by BIOS\n");
> > + mktme_status = MKTME_DISABLED;
> > + goto out;
>
> I think it is pointless to read keyID bits staff if TME is not even
> enabled.
>
> > + }
> > +
> > + pr_info("TME: enabled by BIOS\n");
> > +
> > + tme_policy = TME_ACTIVATE_POLICY(tme_activate);
> > + if (tme_policy != TME_ACTIVATE_POLICY_AES_XTS)
> > + pr_warn("TME: Unknown policy is active: %#llx\n",
> > tme_policy);
> > +
> > + tme_crypto_algs = TME_ACTIVATE_CRYPTO_ALGS(tme_activate);
> > + if (!(tme_crypto_algs & TME_ACTIVATE_CRYPTO_AES_XTS)) {
> > + pr_err("MKTME: No known encryption algorithm is
> > supported: %#llx\n",
> > + tme_crypto_algs);
> > + mktme_status = MKTME_DISABLED;
> > + }
>
> To me it is a little bit confusing about the naming. tme_policy is the
> crypto_alg used by TME keyID (0), and tme_crypto_algs is bitmap of
> supported crypto_algs for MK-TME. Probably a better naming is needed?
> And the naming of TME_ACTIVATE_POLICY(x), TME_ACTIVATE_CRYPTO_ALGS(x)
> above as well?

Suggestions?

--
Kirill A. Shutemov

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