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Message-ID: <DM8PR11MB575000AEB9CC3A318651AAABE7A42@DM8PR11MB5750.namprd11.prod.outlook.com>
Date: Mon, 24 Mar 2025 12:26:38 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
CC: "Hansen, Dave" <dave.hansen@...el.com>, "linux-sgx@...r.kernel.org"
<linux-sgx@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, "Mallick,
Asit K" <asit.k.mallick@...el.com>, "Scarlata, Vincent R"
<vincent.r.scarlata@...el.com>, "Cai, Chong" <chongc@...gle.com>, "Aktas,
Erdem" <erdemaktas@...gle.com>, "Annapurve, Vishal" <vannapurve@...gle.com>,
"dionnaglaze@...gle.com" <dionnaglaze@...gle.com>, "bondarn@...gle.com"
<bondarn@...gle.com>, "Raynor, Scott" <scott.raynor@...el.com>, "Zhang,
Cathy" <cathy.zhang@...el.com>
Subject: RE: [PATCH 4/4] x86/sgx: Implement ENCLS[EUPDATESVN] and
opportunistically call it during first EPC page alloc
> On Fri, Mar 21, 2025 at 02:34:43PM +0200, Elena Reshetova wrote:
> > SGX architecture introduced a new instruction called EUPDATESVN [1]
> > to Ice Lake. It allows updating security SVN version, given that EPC
> > is completely empty. The latter is required for security reasons
> > in order to reason that enclave security posture is as secure as the
> > security SVN version of the TCB that created it.
> >
> > Additionally it is important to ensure that while ENCLS[EUPDATESVN]
> > runs, no concurrent page creation happens in EPC, because it might
> > result in #GP delivered to the creator. Legacy SW might not be prepared
> > to handle such unexpected #GPs and therefore this patch introduces
> > a locking mechanism to ensure no concurrent EPC allocations can happen.
> >
> > It is also ensured that ENCLS[EUPDATESVN] is not called when running
> > in a VM since it does not have a meaning in this context (microcode
> > updates application is limited to the host OS) and will create
> > unnecessary load.
> >
> > The implementation of ENCLS[EUPDATESVN] is based on previous
> submision in [2]
> >
> > [1] https://cdrdv2.intel.com/v1/dl/getContent/648682?explicitVersion=true
>
> I don't think for Intel opcodes a link is needed. We know where to look
> them up.
Ok, I can drop this reference. It is just a whitepaper explaining to readers
the background and operation of EUPDATESVN. It is not part of standard
SDM, so I thought I would put a link.
>
> > [2] https://lore.kernel.org/all/20220520103904.1216-1-
> cathy.zhang@...el.com/T/#medb89e6a916337b4f9e68c736a295ba0ae99ac90
>
> Link:
? Not sure what you mean by it.
>
> >
> > Co-developed-by: Cathy Zhang <cathy.zhang@...el.com>
> > Signed-off-by: Cathy Zhang <cathy.zhang@...el.com>
> > Co-developed-by: Elena Reshetova <elena.reshetova@...el.com>
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> > ---
> > arch/x86/include/asm/sgx.h | 33 +++++++++--------
> > arch/x86/kernel/cpu/sgx/encls.h | 6 +++
> > arch/x86/kernel/cpu/sgx/main.c | 65
> ++++++++++++++++++++++++++++++++-
> > arch/x86/kernel/cpu/sgx/sgx.h | 2 +
> > 4 files changed, 90 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> > index 8ba39bbf4e91..5caf5c31ebc6 100644
> > --- a/arch/x86/include/asm/sgx.h
> > +++ b/arch/x86/include/asm/sgx.h
> > @@ -26,23 +26,26 @@
> > #define SGX_CPUID_EPC_SECTION 0x1
> > /* The bitmask for the EPC section type. */
> > #define SGX_CPUID_EPC_MASK GENMASK(3, 0)
> > +/* EUPDATESVN presence indication */
> > +#define SGX_CPUID_EUPDATESVN BIT(10)
> >
> > enum sgx_encls_function {
> > - ECREATE = 0x00,
> > - EADD = 0x01,
> > - EINIT = 0x02,
> > - EREMOVE = 0x03,
> > - EDGBRD = 0x04,
> > - EDGBWR = 0x05,
> > - EEXTEND = 0x06,
> > - ELDU = 0x08,
> > - EBLOCK = 0x09,
> > - EPA = 0x0A,
> > - EWB = 0x0B,
> > - ETRACK = 0x0C,
> > - EAUG = 0x0D,
> > - EMODPR = 0x0E,
> > - EMODT = 0x0F,
> > + ECREATE = 0x00,
> > + EADD = 0x01,
> > + EINIT = 0x02,
> > + EREMOVE = 0x03,
> > + EDGBRD = 0x04,
> > + EDGBWR = 0x05,
> > + EEXTEND = 0x06,
> > + ELDU = 0x08,
> > + EBLOCK = 0x09,
> > + EPA = 0x0A,
> > + EWB = 0x0B,
> > + ETRACK = 0x0C,
> > + EAUG = 0x0D,
> > + EMODPR = 0x0E,
> > + EMODT = 0x0F,
> > + EUPDATESVN = 0x18,
> > };
> >
> > /**
> > diff --git a/arch/x86/kernel/cpu/sgx/encls.h
> b/arch/x86/kernel/cpu/sgx/encls.h
> > index 99004b02e2ed..3d83c76dc91f 100644
> > --- a/arch/x86/kernel/cpu/sgx/encls.h
> > +++ b/arch/x86/kernel/cpu/sgx/encls.h
> > @@ -233,4 +233,10 @@ static inline int __eaug(struct sgx_pageinfo *pginfo,
> void *addr)
> > return __encls_2(EAUG, pginfo, addr);
> > }
> >
> > +/* Update CPUSVN at runtime. */
> > +static inline int __eupdatesvn(void)
> > +{
> > + return __encls_ret_1(EUPDATESVN, "");
> > +}
> > +
> > #endif /* _X86_ENCLS_H */
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c
> b/arch/x86/kernel/cpu/sgx/main.c
> > index b61d3bad0446..698921229094 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -32,6 +32,11 @@ static DEFINE_XARRAY(sgx_epc_address_space);
> > static LIST_HEAD(sgx_active_page_list);
> > static DEFINE_SPINLOCK(sgx_reclaimer_lock);
> >
> > +/* This lock is held to prevent new EPC pages from being created
> > + * during the execution of ENCLS[EUPDATESVN].
> > + */
> > +static DEFINE_SPINLOCK(sgx_epc_eupdatesvn_lock);
> > +
> > static atomic_long_t sgx_nr_used_pages = ATOMIC_LONG_INIT(0);
> > static unsigned long sgx_nr_total_pages;
> >
> > @@ -457,7 +462,17 @@ static struct sgx_epc_page
> *__sgx_alloc_epc_page_from_node(int nid)
> > page->flags = 0;
> >
> > spin_unlock(&node->lock);
> > - atomic_long_inc(&sgx_nr_used_pages);
> > +
> > + if (!atomic_long_inc_not_zero(&sgx_nr_used_pages)) {
> > + spin_lock(&sgx_epc_eupdatesvn_lock);
> > + /* Only call sgx_updatesvn() once the first enclave's
> > + * page is allocated from EPC
> > + */
> > + if (atomic_long_read(&sgx_nr_used_pages) == 0)
> > + sgx_updatesvn();
> > + atomic_long_inc(&sgx_nr_used_pages);
> > + spin_unlock(&sgx_epc_eupdatesvn_lock);
> > + }
> >
> > return page;
> > }
> > @@ -970,3 +985,51 @@ static int __init sgx_init(void)
> > }
> >
> > device_initcall(sgx_init);
> > +
> > +/**
> > + * sgx_updatesvn() - Issue ENCLS[EUPDATESVN]
> > + * If EPC is ready, this instruction will update CPUSVN to the currently
> > + * loaded microcode update SVN and generate new cryptographic assets.
> > + */
> > +void sgx_updatesvn(void)
> > +{
> > + int ret;
> > + int retry = 10;
>
> Reverse declaration order.
Sure, will fix.
>
> > +
> > + lockdep_assert_held(&sgx_epc_eupdatesvn_lock);
> > +
> > + /* Do not execute EUPDATESVN if instruction is unavalible or running
> in a VM */
> > + if (!(cpuid_eax(SGX_CPUID) & SGX_CPUID_EUPDATESVN) ||
> > + boot_cpu_has(X86_FEATURE_HYPERVISOR))
> > + return;
>
>
> if (!(cpuid_eax(SGX_CPUID) & SGX_CPUID_EUPDATESVN))
> return;
>
> /* ... */
> if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
> return;
>
> The first check really does not need a comment. The second would benefit
> from explaining why bail out inside a VM.
Sure, I can change. The reason why we dont want the execution in a VM is explained
in the commit message, I can duplicate it in the code comment also.
>
>
>
>
>
> > +
> > + do {
> > + ret = __eupdatesvn();
> > + if (ret != SGX_INSUFFICIENT_ENTROPY)
> > + break;
> > +
> > + } while (--retry);
> > +
> > + switch (ret) {
> > + case 0:
> > + pr_debug("EUPDATESVN was successful!\n");
> > + break;
> > + case SGX_NO_UPDATE:
> > + pr_debug("EUPDATESVN was successful, but CPUSVN was not
> updated, "
> > + "because current SVN was not newer than
> CPUSVN.\n");
> > + break;
> > + case SGX_EPC_NOT_READY:
> > + pr_debug("EPC is not ready for SVN update.");
> > + break;
> > + case SGX_INSUFFICIENT_ENTROPY:
> > + pr_debug("CPUSVN update is failed due to Insufficient
> entropy in RNG, "
> > + "please try it later.\n");
> > + break;
> > + case SGX_EPC_PAGE_CONFLICT:
> > + pr_debug("CPUSVN update is failed due to concurrency
> violation, please "
> > + "stop running any other ENCLS leaf and try it
> later.\n");
> > + break;
> > + default:
> > + break;
>
> Remove pr_debug() statements.
This I am not sure it is good idea. I think it would be useful for system
admins to have a way to see that update either happened or not.
It is true that you can find this out by requesting a new SGX attestation
quote (and see if newer SVN is used), but it is not the faster way.
>
> > + }
> > +}
> > diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
> > index d2dad21259a8..92c9e226f1b5 100644
> > --- a/arch/x86/kernel/cpu/sgx/sgx.h
> > +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> > @@ -104,4 +104,6 @@ static inline int __init sgx_vepc_init(void)
> >
> > void sgx_update_lepubkeyhash(u64 *lepubkeyhash);
> >
>
> I don't think we need a newline in-between.
Sure, will fix.
Thank you very much for your prompt review Jarkko!
Best Regards,
Elena.
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