Re: [PATCH V3 17/30] x86/sgx: Support modifying SGX page type

Jarkko Sakkinen
2022-04-05T22:23:54Z

On Tue, 2022-04-05 at 10:06 +0300, Jarkko Sakkinen wrote:
> On Mon, Apr 04, 2022 at 09:49:25AM -0700, Reinette Chatre wrote:
> > Every enclave contains one or more Thread Control Structures (TCS). The
> > TCS contains meta-data used by the hardware to save and restore thread
> > specific information when entering/exiting the enclave. With SGX1 an
> > enclave needs to be created with enough TCSs to support the largest
> > number of threads expecting to use the enclave and enough enclave pages
> > to meet all its anticipated memory demands. In SGX1 all pages remain in
> > the enclave until the enclave is unloaded.
> >
> > SGX2 introduces a new function, ENCLS[EMODT], that is used to change
> > the type of an enclave page from a regular (SGX_PAGE_TYPE_REG) enclave
> > page to a TCS (SGX_PAGE_TYPE_TCS) page or change the type from a
> > regular (SGX_PAGE_TYPE_REG) or TCS (SGX_PAGE_TYPE_TCS)
> > page to a trimmed (SGX_PAGE_TYPE_TRIM) page (setting it up for later
> > removal).
> >
> > With the existing support of dynamically adding regular enclave pages
> > to an initialized enclave and changing the page type to TCS it is
> > possible to dynamically increase the number of threads supported by an
> > enclave.
> >
> > Changing the enclave page type to SGX_PAGE_TYPE_TRIM is the first step
> > of dynamically removing pages from an initialized enclave. The complete
> > page removal flow is:
> > 1) Change the type of the pages to be removed to SGX_PAGE_TYPE_TRIM
> >    using the SGX_IOC_ENCLAVE_MODIFY_TYPE ioctl() introduced here.
> > 2) Approve the page removal by running ENCLU[EACCEPT] from within
> >    the enclave.
> > 3) Initiate actual page removal using the ioctl() introduced in the
> >    following patch.
> >
> > Add ioctl() SGX_IOC_ENCLAVE_MODIFY_TYPE to support changing SGX
> > enclave page types within an initialized enclave. With
> > SGX_IOC_ENCLAVE_MODIFY_TYPE the user specifies a page range and the
> > enclave page type to be applied to all pages in the provided range.
> > The ioctl() itself can return an error code based on failures
> > encountered by the kernel. It is also possible for SGX specific
> > failures to be encountered.  Add a result output parameter to
> > communicate the SGX return code. It is possible for the enclave page
> > type change request to fail on any page within the provided range.
> > Support partial success by returning the number of pages that were
> > successfully changed.
> >
> > After the page type is changed the page continues to be accessible
> > from the kernel perspective with page table entries and internal
> > state. The page may be moved to swap. Any access until ENCLU[EACCEPT]
> > will encounter a page fault with SGX flag set in error code.
> >
> > Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> > ---
> > Changes since V2:
> > - Adjust ioctl number after removal of SGX_IOC_ENCLAVE_RELAX_PERMISSIONS.
> > - Remove attempt at runtime tracking of EPCM permissions
> >   (sgx_encl_page->vm_run_prot_bits). (Jarkko)
> > - Change names to follow guidance of using detailed names (Jarkko):
> >   struct sgx_enclave_modt -> struct sgx_enclave_modify_type
> >   sgx_enclave_modt() -> sgx_enclave_modify_type()
> >   sgx_ioc_enclave_modt() -> sgx_ioc_enclave_modify_type()
> >
> > Changes since V1:
> > - Remove the "Earlier changes ..." paragraph (Jarkko).
> > - Change "new ioctl" text to "Add SGX_IOC_ENCLAVE_MOD_TYPE" (Jarkko).
> > - Discussion about EPCM interaction and the EPCM MODIFIED bit is moved
> >   to new patch that introduces the ENCLS[EMODT] wrapper while keeping
> >   the higher level discussion on page accessibility in
> >   this commit log (Jarkko).
> > - Rename SGX_IOC_PAGE_MODT ioctl() to SGX_IOC_ENCLAVE_MODIFY_TYPE
> >   (Jarkko).
> > - Rename struct sgx_page_modt to struct sgx_enclave_modt in support
> >   of ioctl() rename.
> > - Rename sgx_page_modt() to sgx_enclave_modt() and sgx_ioc_page_modt()
> >   to sgx_ioc_enclave_modt() in support of ioctl() rename.
> > - Provide secinfo as parameter to ioctl() instead of just
> >   page type (Jarkko).
> > - Update comments to refer to new ioctl() names.
> > - Use new SGX2 checking helper().
> > - Use ETRACK flow utility.
> > - Move kernel-doc to function that provides documentation for
> >   Documentation/x86/sgx.rst.
> > - Remove redundant comment.
> > - Use offset/length validation utility.
> > - Make explicit which members of struct sgx_enclave_modt are for
> >   output (Dave).
> >
> >  arch/x86/include/uapi/asm/sgx.h |  20 +++
> >  arch/x86/kernel/cpu/sgx/ioctl.c | 209 ++++++++++++++++++++++++++++++++
> >  2 files changed, 229 insertions(+)
> >
> > diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> > index a0a24e94fb27..529f4ab28410 100644
> > --- a/arch/x86/include/uapi/asm/sgx.h
> > +++ b/arch/x86/include/uapi/asm/sgx.h
> > @@ -31,6 +31,8 @@ enum sgx_page_flags {
> >         _IO(SGX_MAGIC, 0x04)
> >  #define SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS \
> >         _IOWR(SGX_MAGIC, 0x05, struct sgx_enclave_restrict_permissions)
> > +#define SGX_IOC_ENCLAVE_MODIFY_TYPE \
> > +       _IOWR(SGX_MAGIC, 0x06, struct sgx_enclave_modify_type)
> >
> >  /**
> >   * struct sgx_enclave_create - parameter structure for the
> > @@ -97,6 +99,24 @@ struct sgx_enclave_restrict_permissions {
> >         __u64 count;
> >  };
> >
> > +/**
> > + * struct sgx_enclave_modify_type - parameters for %SGX_IOC_ENCLAVE_MODIFY_TYPE
> > + * @offset:    starting page offset (page aligned relative to enclave base
> > + *             address defined in SECS)
> > + * @length:    length of memory (multiple of the page size)
> > + * @secinfo:   address for the SECINFO data containing the new type
> > + *             for pages in range described by @offset and @length
> > + * @result:    (output) SGX result code of ENCLS[EMODT] function
> > + * @count:     (output) bytes successfully changed (multiple of page size)
> > + */
> > +struct sgx_enclave_modify_type {
> > +       __u64 offset;
> > +       __u64 length;
> > +       __u64 secinfo;
> > +       __u64 result;
> > +       __u64 count;
> > +};
> > +
> >  struct sgx_enclave_run;
> >
> >  /**
> > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> > index 4d88bfd163e7..6f769e67ec2d 100644
> > --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> > @@ -898,6 +898,212 @@ static long sgx_ioc_enclave_restrict_permissions(struct sgx_encl *encl,
> >         return ret;
> >  }
> >
> > +/**
> > + * sgx_enclave_modify_type() - Modify type of SGX enclave pages
> > + * @encl:      Enclave to which the pages belong.
> > + * @modt:      Checked parameters from user about which pages need modifying.
> > + * @page_type: New page type.
> > + *
> > + * Return:
> > + * - 0:                Success
> > + * - -errno:   Otherwise
> > + */
> > +static long sgx_enclave_modify_type(struct sgx_encl *encl,
> > +                                   struct sgx_enclave_modify_type *modt,
> > +                                   enum sgx_page_type page_type)
> > +{
> > +       unsigned long max_prot_restore;
> > +       struct sgx_encl_page *entry;
> > +       struct sgx_secinfo secinfo;
> > +       unsigned long prot;
> > +       unsigned long addr;
> > +       unsigned long c;
> > +       void *epc_virt;
> > +       int ret;
> > +
> > +       /*
> > +        * The only new page types allowed by hardware are PT_TCS and PT_TRIM.
> > +        */
> > +       if (page_type != SGX_PAGE_TYPE_TCS && page_type != SGX_PAGE_TYPE_TRIM)
> > +               return -EINVAL;
> > +
> > +       memset(&secinfo, 0, sizeof(secinfo));
> > +
> > +       secinfo.flags = page_type << 8;
> > +
> > +       for (c = 0 ; c < modt->length; c += PAGE_SIZE) {
> > +               addr = encl->base + modt->offset + c;
> > +
> > +               mutex_lock(&encl->lock);
> > +
> > +               entry = sgx_encl_load_page(encl, addr);
> > +               if (IS_ERR(entry)) {
> > +                       ret = PTR_ERR(entry) == -EBUSY ? -EAGAIN : -EFAULT;
> > +                       goto out_unlock;
> > +               }
> > +
> > +               /*
> > +                * Borrow the logic from the Intel SDM. Regular pages
> > +                * (SGX_PAGE_TYPE_REG) can change type to SGX_PAGE_TYPE_TCS
> > +                * or SGX_PAGE_TYPE_TRIM but TCS pages can only be trimmed.
> > +                * CET pages not supported yet.
> > +                */
> > +               if (!(entry->type == SGX_PAGE_TYPE_REG ||
> > +                     (entry->type == SGX_PAGE_TYPE_TCS &&
> > +                      page_type == SGX_PAGE_TYPE_TRIM))) {
> > +                       ret = -EINVAL;
> > +                       goto out_unlock;
> > +               }
> > +
> > +               max_prot_restore = entry->vm_max_prot_bits;
> > +
> > +               /*
> > +                * Once a regular page becomes a TCS page it cannot be
> > +                * changed back. So the maximum allowed protection reflects
> > +                * the TCS page that is always RW from kernel perspective but
> > +                * will be inaccessible from within enclave. Before doing
> > +                * so, do make sure that the new page type continues to
> > +                * respect the originally vetted page permissions.
> > +                */
> > +               if (entry->type == SGX_PAGE_TYPE_REG &&
> > +                   page_type == SGX_PAGE_TYPE_TCS) {
> > +                       if (~entry->vm_max_prot_bits & (VM_READ | VM_WRITE)) {
> > +                               ret = -EPERM;
> > +                               goto out_unlock;
> > +                       }
> > +                       prot = PROT_READ | PROT_WRITE;
> > +                       entry->vm_max_prot_bits = calc_vm_prot_bits(prot, 0);
> > +
> > +                       /*
> > +                        * Prevent page from being reclaimed while mutex
> > +                        * is released.
> > +                        */
> > +                       if (sgx_unmark_page_reclaimable(entry->epc_page)) {
> > +                               ret = -EAGAIN;
> > +                               goto out_entry_changed;
> > +                       }
> > +
> > +                       /*
> > +                        * Do not keep encl->lock because of dependency on
> > +                        * mmap_lock acquired in sgx_zap_enclave_ptes().
> > +                        */
> > +                       mutex_unlock(&encl->lock);
> > +
> > +                       sgx_zap_enclave_ptes(encl, addr);
> > +
> > +                       mutex_lock(&encl->lock);
> > +
> > +                       sgx_mark_page_reclaimable(entry->epc_page);
> > +               }
> > +
> > +               /* Change EPC type */
> > +               epc_virt = sgx_get_epc_virt_addr(entry->epc_page);
> > +               ret = __emodt(&secinfo, epc_virt);
> > +               if (encls_faulted(ret)) {
> > +                       /*
> > +                        * All possible faults should be avoidable:
> > +                        * parameters have been checked, will only change
> > +                        * valid page types, and no concurrent
> > +                        * SGX1/SGX2 ENCLS instructions since these are
> > +                        * protected with mutex.
> > +                        */
> > +                       pr_err_once("EMODT encountered exception %d\n",
> > +                                   ENCLS_TRAPNR(ret));
> > +                       ret = -EFAULT;
> > +                       goto out_entry_changed;
> > +               }
> > +               if (encls_failed(ret)) {
> > +                       modt->result = ret;
> > +                       ret = -EFAULT;
> > +                       goto out_entry_changed;
> > +               }
> > +
> > +               ret = sgx_enclave_etrack(encl);
> > +               if (ret) {
> > +                       ret = -EFAULT;
> > +                       goto out_unlock;
> > +               }
> > +
> > +               entry->type = page_type;
> > +
> > +               mutex_unlock(&encl->lock);
> > +       }
> > +
> > +       ret = 0;
> > +       goto out;
> > +
> > +out_entry_changed:
> > +       entry->vm_max_prot_bits = max_prot_restore;
> > +out_unlock:
> > +       mutex_unlock(&encl->lock);
> > +out:
> > +       modt->count = c;
> > +
> > +       return ret;
> > +}
> > +
> > +/**
> > + * sgx_ioc_enclave_modify_type() - handler for %SGX_IOC_ENCLAVE_MODIFY_TYPE
> > + * @encl:      an enclave pointer
> > + * @arg:       userspace pointer to a &struct sgx_enclave_modify_type instance
> > + *
> > + * Ability to change the enclave page type supports the following use cases:
> > + *
> > + * * It is possible to add TCS pages to an enclave by changing the type of
> > + *   regular pages (%SGX_PAGE_TYPE_REG) to TCS (%SGX_PAGE_TYPE_TCS) pages.
> > + *   With this support the number of threads supported by an initialized
> > + *   enclave can be increased dynamically.
> > + *
> > + * * Regular or TCS pages can dynamically be removed from an initialized
> > + *   enclave by changing the page type to %SGX_PAGE_TYPE_TRIM. Changing the
> > + *   page type to %SGX_PAGE_TYPE_TRIM marks the page for removal with actual
> > + *   removal done by handler of %SGX_IOC_ENCLAVE_REMOVE_PAGES ioctl() called
> > + *   after ENCLU[EACCEPT] is run on %SGX_PAGE_TYPE_TRIM page from within the
> > + *   enclave.
> > + *
> > + * Return:
> > + * - 0:                Success
> > + * - -errno:   Otherwise
> > + */
> > +static long sgx_ioc_enclave_modify_type(struct sgx_encl *encl, void __user *arg)
> > +{
> > +       struct sgx_enclave_modify_type params;
> > +       enum sgx_page_type page_type;
> > +       struct sgx_secinfo secinfo;
> > +       long ret;
> > +
> > +       ret = sgx_ioc_sgx2_ready(encl);
> > +       if (ret)
> > +               return ret;
> > +
> > +       if (copy_from_user(&params, arg, sizeof(params)))
> > +               return -EFAULT;
> > +
> > +       if (sgx_validate_offset_length(encl, params.offset, params.length))
> > +               return -EINVAL;
> > +
> > +       if (copy_from_user(&secinfo, (void __user *)params.secinfo,
> > +                          sizeof(secinfo)))
> > +               return -EFAULT;
> > +
> > +       if (secinfo.flags & ~SGX_SECINFO_PAGE_TYPE_MASK)
> > +               return -EINVAL;
> > +
> > +       if (memchr_inv(secinfo.reserved, 0, sizeof(secinfo.reserved)))
> > +               return -EINVAL;
> > +
> > +       if (params.result || params.count)
> > +               return -EINVAL;
> > +
> > +       page_type = (secinfo.flags & SGX_SECINFO_PAGE_TYPE_MASK) >> 8;
> > +       ret = sgx_enclave_modify_type(encl, &params, page_type);
> > +
> > +       if (copy_to_user(arg, &params, sizeof(params)))
> > +               return -EFAULT;
> > +
> > +       return ret;
> > +}
> > +
> >  long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> >  {
> >         struct sgx_encl *encl = filep->private_data;
> > @@ -923,6 +1129,9 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> >                 ret = sgx_ioc_enclave_restrict_permissions(encl,
> >                                                            (void __user *)arg);
> >                 break;
> > +       case SGX_IOC_ENCLAVE_MODIFY_TYPE:
> > +               ret = sgx_ioc_enclave_modify_type(encl, (void __user *)arg);
> > +               break;
> >         default:
> >                 ret = -ENOIOCTLCMD;
> >                 break;
> > --
> > 2.25.1
> >
>
> To be coherent with other names, this should be
> SGX_IOC_ENCLAVE_MODIFY_TYPES.

This should take only page type given that flags are zeroed:

EPCM(DS:RCX).R := 0;
EPCM(DS:RCX).W := 0;
EPCM(DS:RCX).X := 0;

BR, Jarkko