[PATCH RFC 3/3] x86/sgx: Implement EAUG population with MAP_POPULATE

Jarkko Sakkinen
2022-03-06T05:33:20Z

With SGX1 an enclave needs to be created with its maximum memory demands
pre-allocated. Pages cannot be added to an enclave after it is initialized.
SGX2 introduces a new function, ENCLS[EAUG] for adding pages to an
initialized enclave.

Add support for dynamically adding pages to an initialized enclave with
mmap() by populating pages with EAUG. Use f_ops->populate() callback to
achieve this behaviour.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
arch/x86/kernel/cpu/sgx/driver.c | 129 +++++++++++++++++++++++++++++++
1 file changed, 129 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index aa9b8b868867..0e97e7476076 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -9,6 +9,7 @@
#include <asm/traps.h>
#include "driver.h"
#include "encl.h"
+#include "encls.h"

u64 sgx_attributes_reserved_mask;
u64 sgx_xfrm_reserved_mask = ~0x3;
@@ -101,6 +102,133 @@ static int sgx_mmap(struct file *file, struct vm_area_struct *vma)
return 0;
}

+static int sgx_encl_augment_page(struct sgx_encl *encl, unsigned long offset)
+{
+ struct sgx_pageinfo pginfo = {0};
+ struct sgx_encl_page *encl_page;
+ struct sgx_epc_page *epc_page;
+ struct sgx_va_page *va_page;
+ u64 secinfo_flags;
+ int ret;
+
+ /*
+ * Ignore internal permission checking for dynamically added pages.
+ * They matter only for data added during the pre-initialization phase.
+ * The enclave decides the permissions by the means of EACCEPT,
+ * EACCEPTCOPY and EMODPE.
+ */
+ secinfo_flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_X;
+ encl_page = sgx_encl_page_alloc(encl, offset, secinfo_flags);
+ if (IS_ERR(encl_page))
+ return PTR_ERR(encl_page);
+
+ epc_page = sgx_alloc_epc_page(encl_page, true);
+ if (IS_ERR(epc_page)) {
+ ret = PTR_ERR(epc_page);
+ goto err_alloc_epc_page;
+ }
+
+ va_page = sgx_encl_grow(encl);
+ if (IS_ERR(va_page)) {
+ ret = PTR_ERR(va_page);
+ goto err_grow;
+ }
+
+ mutex_lock(&encl->lock);
+
+ /*
+ * Adding to encl->va_pages must be done under encl->lock. Ditto for
+ * deleting (via sgx_encl_shrink()) in the error path.
+ */
+ if (va_page)
+ list_add(&va_page->list, &encl->va_pages);
+
+ /*
+ * Insert prior to EADD in case of OOM. EADD modifies MRENCLAVE, i.e.
+ * can't be gracefully unwound, while failure on EADD/EXTEND is limited
+ * to userspace errors (or kernel/hardware bugs).
+ */
+ ret = xa_insert(&encl->page_array, PFN_DOWN(encl_page->desc),
+ encl_page, GFP_KERNEL);
+
+ /*
+ * If ret == -EBUSY then page was created in another flow while
+ * running without encl->lock
+ */
+ if (ret)
+ goto err_xa_insert;
+
+ pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page);
+ pginfo.addr = encl_page->desc & PAGE_MASK;
+ pginfo.metadata = 0;
+
+ ret = __eaug(&pginfo, sgx_get_epc_virt_addr(epc_page));
+ if (ret)
+ goto err_eaug;
+
+ encl_page->encl = encl;
+ encl_page->epc_page = epc_page;
+ encl_page->type = SGX_PAGE_TYPE_REG;
+ encl->secs_child_cnt++;
+
+ sgx_mark_page_reclaimable(encl_page->epc_page);
+
+ mutex_unlock(&encl->lock);
+
+ return 0;
+
+err_eaug:
+ xa_erase(&encl->page_array, PFN_DOWN(encl_page->desc));
+
+err_xa_insert:
+ sgx_encl_shrink(encl, va_page);
+ mutex_unlock(&encl->lock);
+
+err_grow:
+ sgx_encl_free_epc_page(epc_page);
+
+err_alloc_epc_page:
+ kfree(encl_page);
+
+ return VM_FAULT_SIGBUS;
+}
+
+/*
+ * Add new pages to the enclave sequentially with ENCLS[EAUG]. Note that
+ * sgx_mmap() validates that the given VMA is within the enclave range. Calling
+ * here sgx_encl_may_map() second time would too time consuming.
+ */
+static int sgx_populate(struct file *file, struct vm_area_struct *vma)
+{
+ unsigned long length = vma->vm_end - vma->vm_start;
+ struct sgx_encl *encl = file->private_data;
+ unsigned long start = encl->base - vma->vm_start;
+ unsigned long pos;
+ int ret;
+
+ /* EAUG works only for initialized enclaves. */
+ if (!test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
+ return -EINVAL;
+
+ for (pos = 0 ; pos < length; pos += PAGE_SIZE) {
+ if (signal_pending(current)) {
+ if (!pos)
+ ret = -ERESTARTSYS;
+
+ break;
+ }
+
+ if (need_resched())
+ cond_resched();
+
+ ret = sgx_encl_augment_page(encl, start + pos);
+ if (ret)
+ break;
+ }
+
+ return ret;
+}
+
static unsigned long sgx_get_unmapped_area(struct file *file,
unsigned long addr,
unsigned long len,
@@ -133,6 +261,7 @@ static const struct file_operations sgx_encl_fops = {
.compat_ioctl = sgx_compat_ioctl,
#endif
.mmap = sgx_mmap,
+ .populate = sgx_populate,
.get_unmapped_area = sgx_get_unmapped_area,
};

--
2.35.1