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

Jarkko Sakkinen
2022-04-25T13:59:40Z

On Sun, 2022-04-24 at 02:27 +0000, Zhang, Cathy wrote:
> 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;

Yeah, quickly skimmed, looks right.

BR, Jarkko