RE: [PATCH v4 1/9] x86/sgx: Introduce mechanism to prevent new initializations of EPC pages

Zhang, Cathy
2022-04-24T02:27:50Z

Hi Jarkko,

> -----Original Message-----
> From: Jarkko Sakkinen <jarkko@kernel.org>
> Sent: Friday, April 22, 2022 12:02 AM
> To: Zhang, Cathy <cathy.zhang@intel.com>
> Cc: linux-sgx@vger.kernel.org; x86@kernel.org; Chatre, Reinette
> <reinette.chatre@intel.com>; Hansen, Dave <dave.hansen@intel.com>; Raj,
> Ashok <ashok.raj@intel.com>; Peng, Chao P <chao.p.peng@intel.com>;
> Zhong, Yang <yang.zhong@intel.com>
> Subject: Re: [PATCH v4 1/9] x86/sgx: Introduce mechanism to prevent new
> initializations of EPC pages
>
> On Thu, Apr 21, 2022 at 07:03:18PM +0800, Cathy Zhang wrote:
> > == Background ==
> >
> > EUPDATESVN is a new SGX instruction which allows enclave attestation
> > to include information about updated microcode without a reboot.
> >
> > The SGX hardware maintains metadata for each enclave page to help
> > enforce its security guarantees. This includes things like a record of
> > the enclave to which the page belongs and the type of the page:
> > SGX metadata like "VA" or "SECS" pages, or regular enclave pages like
> > those that store user data.
> >
> > Before an EUPDATESVN operation can be successful, all SGX memory (aka.
> > EPC) must be marked as "unused" in the SGX hardware metadata (aka,
> > EPCM). The SGX microcode now maintains a reference count of pages
> > which are unused to aid in determining when all pages reach the
> > "unused" state.
> >
> > Both bare-metal and KVM guest EPC must be made unused. To increase the
> > chance of a successful EUPDATESVN, the kernel prevents existing
> > enclaves from creating new, valid pages and prevents new enclave
> > creation (creating an enclave involves initializing a "SECS" page).
> >
> > The entire EUPDATESVN process is very slow since it potentially
> > affects gigabytes of enclave memory. It can potentially take seconds
> > or minutes to complete. Userspace may encounter -EBUSY errors during
> > the update and is expected to retry.
> >
> > == Patch contents ==
> >
> > Introduce mechanism to prevent new initializations of EPC pages.
> >
> > Use a flag to indicate when SGX EPC pages are "locked", which means
> > it's not allowed to allocate new EPC page for use. Check it in all
> > paths that can initialize an EPC page. Use SRCU to ensure that the
> > flag is visible across the system before proceeding with an update.
> >
> > Add checks to all sites that call SGX instructions that can transition
> > pages from unused to initialized to ensure that the SRCU lock is held.
> >
> > Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>
> >
> > ---
> > Changes since v3:
> > - Rename lable "out" as "err" in sgx_ioc_enclave_create, update error
> > branch accordingly. (Jarrko Sakkinen)
> >
> > Changes since v2:
> > - Move out the SGX2 related change to remove the dependency.
> > (Jarkko Sakkinen, Reinette Chatre).
> > ---
> > arch/x86/kernel/cpu/sgx/encls.h | 8 ++++++
> > arch/x86/kernel/cpu/sgx/sgx.h | 3 +++
> > arch/x86/kernel/cpu/sgx/encl.c | 19 +++++++++++++++
> > arch/x86/kernel/cpu/sgx/ioctl.c | 43 +++++++++++++++++++++++++++------
> > arch/x86/kernel/cpu/sgx/main.c | 37 ++++++++++++++++++++++++++++
> > arch/x86/kernel/cpu/sgx/virt.c | 20 +++++++++++++++
> > 6 files changed, 123 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/sgx/encls.h
> > b/arch/x86/kernel/cpu/sgx/encls.h index fa04a73daf9c..60321c5f5718
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/encls.h
> > +++ b/arch/x86/kernel/cpu/sgx/encls.h
> > @@ -138,6 +138,8 @@ static inline bool encls_failed(int ret)
> >
> > static inline int __ecreate(struct sgx_pageinfo *pginfo, void *secs)
> > {
> > + lockdep_assert_held(&sgx_lock_epc_srcu);
> > +
> > return __encls_2(ECREATE, pginfo, secs); }
> >
> > @@ -148,6 +150,8 @@ static inline int __eextend(void *secs, void
> > *addr)
> >
> > static inline int __eadd(struct sgx_pageinfo *pginfo, void *addr) {
> > + lockdep_assert_held(&sgx_lock_epc_srcu);
> > +
> > return __encls_2(EADD, pginfo, addr); }
> >
> > @@ -179,6 +183,8 @@ static inline int __etrack(void *addr) static
> > inline int __eldu(struct sgx_pageinfo *pginfo, void *addr,
> > void *va)
> > {
> > + lockdep_assert_held(&sgx_lock_epc_srcu);
> > +
> > return __encls_ret_3(ELDU, pginfo, addr, va); }
> >
> > @@ -191,6 +197,8 @@ static inline int __epa(void *addr) {
> > unsigned long rbx = SGX_PAGE_TYPE_VA;
> >
> > + lockdep_assert_held(&sgx_lock_epc_srcu);
> > +
> > return __encls_2(EPA, rbx, addr);
> > }
> >
> > diff --git a/arch/x86/kernel/cpu/sgx/sgx.h
> > b/arch/x86/kernel/cpu/sgx/sgx.h index b30cee4de903..d7a1490d90bb
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/sgx.h
> > +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> > @@ -103,4 +103,7 @@ static inline int __init sgx_vepc_init(void)
> >
> > void sgx_update_lepubkeyhash(u64 *lepubkeyhash);
> >
> > +extern struct srcu_struct sgx_lock_epc_srcu; bool
> > +sgx_epc_is_locked(void);
> > +
> > #endif /* _X86_SGX_H */
> > diff --git a/arch/x86/kernel/cpu/sgx/encl.c
> > b/arch/x86/kernel/cpu/sgx/encl.c index 02ff9ac83985..68c8d65a8dee
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/encl.c
> > +++ b/arch/x86/kernel/cpu/sgx/encl.c
> > @@ -142,6 +142,7 @@ static vm_fault_t sgx_vma_fault(struct vm_fault
> *vmf)
> > unsigned long phys_addr;
> > struct sgx_encl *encl;
> > vm_fault_t ret;
> > + int srcu_idx;
> >
> > encl = vma->vm_private_data;
> >
> > @@ -153,11 +154,18 @@ static vm_fault_t sgx_vma_fault(struct vm_fault
> *vmf)
> > if (unlikely(!encl))
> > return VM_FAULT_SIGBUS;
> >
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > + if (sgx_epc_is_locked()) {
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > + return VM_FAULT_SIGBUS;
> > + }
> > +
> > mutex_lock(&encl->lock);
> >
> > entry = sgx_encl_load_page(encl, addr, vma->vm_flags);
> > if (IS_ERR(entry)) {
> > mutex_unlock(&encl->lock);
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> >
> > if (PTR_ERR(entry) == -EBUSY)
> > return VM_FAULT_NOPAGE;
> > @@ -170,12 +178,14 @@ static vm_fault_t sgx_vma_fault(struct vm_fault
> *vmf)
> > ret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr));
> > if (ret != VM_FAULT_NOPAGE) {
> > mutex_unlock(&encl->lock);
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> >
> > return VM_FAULT_SIGBUS;
> > }
> >
> > sgx_encl_test_and_clear_young(vma->vm_mm, entry);
> > mutex_unlock(&encl->lock);
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> >
> > return VM_FAULT_NOPAGE;
> > }
> > @@ -323,6 +333,7 @@ static int sgx_vma_access(struct vm_area_struct
> *vma, unsigned long addr,
> > struct sgx_encl_page *entry = NULL;
> > char data[sizeof(unsigned long)];
> > unsigned long align;
> > + int srcu_idx;
> > int offset;
> > int cnt;
> > int ret = 0;
> > @@ -339,8 +350,15 @@ static int sgx_vma_access(struct vm_area_struct
> *vma, unsigned long addr,
> > return -EFAULT;
> >
> > for (i = 0; i < len; i += cnt) {
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > + if (sgx_epc_is_locked()) {
> > + ret = -EBUSY;
> > + goto out;
> > + }
> > +
> > entry = sgx_encl_reserve_page(encl, (addr + i) & PAGE_MASK,
> > vma->vm_flags);
> > +
> > if (IS_ERR(entry)) {
> > ret = PTR_ERR(entry);
> > break;
> > @@ -366,6 +384,7 @@ static int sgx_vma_access(struct vm_area_struct
> > *vma, unsigned long addr,
> >
> > out:
> > mutex_unlock(&encl->lock);
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> >
> > if (ret)
> > break;
> > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c
> > b/arch/x86/kernel/cpu/sgx/ioctl.c index b3c2e8d58142..a4df72f715d7
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> > @@ -147,24 +147,42 @@ static int sgx_encl_create(struct sgx_encl
> > *encl, struct sgx_secs *secs) static long
> > sgx_ioc_enclave_create(struct sgx_encl *encl, void __user *arg) {
> > struct sgx_enclave_create create_arg;
> > + int srcu_idx;
> > void *secs;
> > int ret;
> >
> > - if (test_bit(SGX_ENCL_CREATED, &encl->flags))
> > - return -EINVAL;
> > + if (test_bit(SGX_ENCL_CREATED, &encl->flags)) {
> > + ret = -EINVAL;
> > + goto err;
> > + }
> >
> > - if (copy_from_user(&create_arg, arg, sizeof(create_arg)))
> > - return -EFAULT;
> > + if (copy_from_user(&create_arg, arg, sizeof(create_arg))) {
> > + ret = -EFAULT;
> > + goto err;
> > + }
> >
> > secs = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > - if (!secs)
> > - return -ENOMEM;
> > + if (!secs) {
> > + ret = -ENOMEM;
> > + goto err;
> > + }
> >
> > if (copy_from_user(secs, (void __user *)create_arg.src, PAGE_SIZE))
> > ret = -EFAULT;
>
> if (copy_from_user(secs, (void __user *)create_arg.src, PAGE_SIZE)) {
> ret = -EFAULT;
> goto err;
> }
>
> Right?

Right! I don't change the if branch for I see it will go to the err label directly.
But it's changed now :-)

>
>
> > - else
> > + else {
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > + if (sgx_epc_is_locked()) {
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > + ret = -EBUSY;
> > + goto err;
> > + }
> > +
> > ret = sgx_encl_create(encl, secs);
> >
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > + }
>
> I mean less branching for the common (success) case.

Do you mean to change as follows:

if (copy_from_user(secs, (void __user *)create_arg.src, PAGE_SIZE)) {
ret = -EFAULT;
goto err;

srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
if (sgx_epc_is_locked()) {
srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
ret = -EBUSY;
goto err;
}

ret = sgx_encl_create(encl, secs);

srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);

err:
kfree(secs);
return ret;

>
> > +
> > +err:
> > kfree(secs);
> > return ret;
> > }
> > @@ -418,6 +436,7 @@ static long sgx_ioc_enclave_add_pages(struct
> sgx_encl *encl, void __user *arg)
> > struct sgx_enclave_add_pages add_arg;
> > struct sgx_secinfo secinfo;
> > unsigned long c;
> > + int srcu_idx;
> > int ret;
> >
> > if (!test_bit(SGX_ENCL_CREATED, &encl->flags) || @@ -455,8 +474,18
> > @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void
> __user *arg)
> > if (need_resched())
> > cond_resched();
> >
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > + if (sgx_epc_is_locked()) {
> > + ret = -EBUSY;
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > + break;
> > + }
> > +
> > ret = sgx_encl_add_page(encl, add_arg.src + c,
> add_arg.offset + c,
> > &secinfo, add_arg.flags);
> > +
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > +
> > if (ret)
> > break;
> > }
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c
> > b/arch/x86/kernel/cpu/sgx/main.c index b3aba1e1274c..10360f06c0df
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -23,6 +23,17 @@ static int sgx_nr_epc_sections; static struct
> > task_struct *ksgxd_tsk; static DECLARE_WAIT_QUEUE_HEAD(ksgxd_waitq);
> > static DEFINE_XARRAY(sgx_epc_address_space);
> > +/*
> > + * The flag sgx_epc_locked prevents any new SGX flows that
> > + * may attempt to allocate a new EPC page.
> > + */
> > +static bool __rcu sgx_epc_locked;
> > +/*
> > + * By synchronizing around sgx_epc_locked SRCU ensures that any
> > +executing
> > + * SGX flows have completed before proceeding with an SVN update. New
> > +SGX flows
> > + * will be prevented from starting during an SVN update.
> > + */
> > +DEFINE_SRCU(sgx_lock_epc_srcu);
> >
> > /*
> > * These variables are part of the state of the reclaimer, and must
> > be accessed @@ -407,6 +418,8 @@ static bool
> > sgx_should_reclaim(unsigned long watermark)
> >
> > static int ksgxd(void *p)
> > {
> > + int srcu_idx;
> > +
> > set_freezable();
> >
> > /*
> > @@ -427,9 +440,15 @@ static int ksgxd(void *p)
> > kthread_should_stop() ||
> >
> sgx_should_reclaim(SGX_NR_HIGH_PAGES));
> >
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > + if (sgx_epc_is_locked())
> > + goto maybe_resched;
> > +
> > if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
> > sgx_reclaim_pages();
> >
> > +maybe_resched:
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > cond_resched();
> > }
> >
> > @@ -972,3 +991,21 @@ static int __init sgx_init(void) }
> >
> > device_initcall(sgx_init);
> > +
> > +static void sgx_lock_epc(void)
> > +{
> > + sgx_epc_locked = true;
> > + synchronize_srcu(&sgx_lock_epc_srcu);
> > +}
> > +
> > +static void sgx_unlock_epc(void)
> > +{
> > + sgx_epc_locked = false;
> > + synchronize_srcu(&sgx_lock_epc_srcu);
> > +}
> > +
> > +bool sgx_epc_is_locked(void)
> > +{
> > + lockdep_assert_held(&sgx_lock_epc_srcu);
> > + return sgx_epc_locked;
> > +}
> > diff --git a/arch/x86/kernel/cpu/sgx/virt.c
> > b/arch/x86/kernel/cpu/sgx/virt.c index 6a77a14eee38..e953816d7c8b
> > 100644
> > --- a/arch/x86/kernel/cpu/sgx/virt.c
> > +++ b/arch/x86/kernel/cpu/sgx/virt.c
> > @@ -75,10 +75,21 @@ static vm_fault_t sgx_vepc_fault(struct vm_fault
> > *vmf) {
> > struct vm_area_struct *vma = vmf->vma;
> > struct sgx_vepc *vepc = vma->vm_private_data;
> > + int srcu_idx;
> > int ret;
> >
> > mutex_lock(&vepc->lock);
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > +
> > + if (sgx_epc_is_locked()) {
> > + ret = -EBUSY;
> > + goto out_unlock;
> > + }
> > +
> > ret = __sgx_vepc_fault(vepc, vma, vmf->address);
> > +
> > +out_unlock:
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > mutex_unlock(&vepc->lock);
> >
> > if (!ret)
> > @@ -331,6 +342,7 @@ int __init sgx_vepc_init(void) int
> > sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
> > int *trapnr)
> > {
> > + int srcu_idx;
> > int ret;
> >
> > /*
> > @@ -347,6 +359,12 @@ int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo,
> void __user *secs,
> > if (WARN_ON_ONCE(!access_ok(secs, PAGE_SIZE)))
> > return -EINVAL;
> >
> > + srcu_idx = srcu_read_lock(&sgx_lock_epc_srcu);
> > + if (sgx_epc_is_locked()) {
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > + return -EBUSY;
> > + }
> > +
> > __uaccess_begin();
> > ret = __ecreate(pageinfo, (void *)secs);
> > __uaccess_end();
> > @@ -356,6 +374,8 @@ int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo,
> void __user *secs,
> > return -EFAULT;
> > }
> >
> > + srcu_read_unlock(&sgx_lock_epc_srcu, srcu_idx);
> > +
> > /* ECREATE doesn't return an error code, it faults or succeeds. */
> > WARN_ON_ONCE(ret);
> > return 0;
> > --
> > 2.17.1
> >
>
> BR, Jarkko