[PATCH v21 18/28] x86/sgx: Add swapping code to the core and SGX driver

From: Jarkko Sakkinen
Date: Sat Jul 13 2019 - 13:11:46 EST

Because the kernel is untrusted, swapping pages in/out of the Enclave
Page Cache (EPC) has specialized requirements:

* The kernel cannot directly access EPC memory, i.e. cannot copy data
to/from the EPC.
* To evict a page from the EPC, the kernel must "prove" to hardware that
are no valid TLB entries for said page since a stale TLB entry would
allow an attacker to bypass SGX access controls.
* When loading a page back into the EPC, hardware must be able to verify
the integrity and freshness of the data.
* When loading an enclave page, e.g. regular pages and Thread Control
Structures (TCS), hardware must be able to associate the page with a
Secure Enclave Control Structure (SECS).

To satisfy the above requirements, the CPU provides dedicated ENCLS
functions to support paging data in/out of the EPC:

* EBLOCK: Mark a page as blocked in the EPC Map (EPCM). Attempting
to access a blocked page that misses the TLB will fault.
* ETRACK: Activate blocking tracking. Hardware verifies that all
translations for pages marked as "blocked" have been flushed
from the TLB.
* EPA: Add version array page to the EPC. As the name suggests, a
VA page is an 512-entry array of version numbers that are
used to uniquely identify pages evicted from the EPC.
* EWB: Write back a page from EPC to memory, e.g. RAM. Software
must supply a VA slot, memory to hold the a Paging Crypto
Metadata (PCMD) of the page and obviously backing for the
evicted page.
* ELD{B,U}: Load a page in {un}blocked state from memory to EPC. The
driver only uses the ELDU variant as there is no use case
for loading a page as "blocked" in a bare metal environment.

To top things off, all of the above ENCLS functions are subject to
strict concurrency rules, e.g. many operations will #GP fault if two
or more operations attempt to access common pages/structures.

To put it succinctly, paging in/out of the EPC requires coordinating
with the SGX driver where all of an enclave's tracking resides. But,
simply shoving all reclaim logic into the driver is not desirable as
doing so has unwanted long term implications:

* Oversubscribing EPC to KVM guests, i.e. virtualizing SGX in KVM and
swapping a guest's EPC pages (without the guest's cooperation) needs
the same high level flows for reclaim but has painfully different
semantics in the details.
* Accounting EPC, i.e. adding an EPC cgroup controller, is desirable
as EPC is effectively a specialized memory type and even more scarce
than system memory. Providing a single touchpoint for EPC accounting
regardless of end consumer greatly simplifies the EPC controller.
* Allowing the userspace-facing driver to be built as a loaded module
is desirable, e.g. for debug, testing and development. The cgroup
infrastructure does not support dependencies on loadable modules.
* Separating EPC swapping from the driver once it has been tightly
coupled to the driver is non-trivial (speaking from experience).

So, although the SGX driver is currently the sole consumer of EPC,
encapsulate EPC swapping in the driver to minimize the dependencies
between the core SGX code and driver, and do so in a way that can be
extended to an abstracted interface with minimal effort.

To that end, add functions to swap EPC pages to the driver. The user
of these functions will be the core SGX subsystem, which will be enabled
in a future patch.

* sgx_encl_page_{get,put}() - Attempt to pin/unpin (the owner of) an EPC
page so that it can be operated on by a reclaimer.
* sgx_encl_page_reclaim() - Mark a page as being reclaimed. The
page is considered reclaimable if it hasn't been accessed recently and
it isn't reserved by the driver for other use.
* sgx_encl_page_block() - EBLOCK an EPC page
* sgx_encl_page_write() - Evict an EPC page to the regular memory via
EWB. Activates ETRACK (via sgx_encl_track()) if necessary.

Since we also need to be able to fault pages back into the EPC, add a
page fault handler to allocate an EPC page and ELDU a previously evicted
page.

Wire up the EPC manager's reclaim flow to the SGX driver's swapping
functionality. In the long term there will be multiple users of the
EPC manager, e.g. SGX driver and KVM, thus the interface between the
EPC manager and the driver is fairly genericized and decoupled. But
to avoid adding unusued infrastructure, do not add any indirection
between the EPC manager and the SGX driver. This has the unfortunate
and odd side effect of preventing the SGX driver from being compiled
as a loadable module. However, this should be a temporary situation
that is remedied when a second user of EPC is added, i.e. KVM.

The swapper thread ksgxswapd reclaims pages on the event when the number
of free EPC pages goes below %SGX_NR_LOW_PAGES up until it reaches
%SGX_NR_HIGH_PAGES.

Pages are reclaimed in LRU fashion from a global list. The consumers
take care of calling EBLOCK (block page from new accesses), ETRACK
(restart counting the entering hardware threads) and EWB (write page to
the regular memory) because executing these operations usually (if not
always) requires to do some subsystem-internal locking operations.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
Co-developed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Co-developed-by: Serge Ayoun <serge.ayoun@xxxxxxxxx>
Signed-off-by: Serge Ayoun <serge.ayoun@xxxxxxxxx>
Co-developed-by: Shay Katz-zamir <shay.katz-zamir@xxxxxxxxx>
Signed-off-by: Shay Katz-zamir <shay.katz-zamir@xxxxxxxxx>
---
arch/x86/kernel/cpu/sgx/driver/ioctl.c | 58 +++-
arch/x86/kernel/cpu/sgx/driver/main.c | 1 +
arch/x86/kernel/cpu/sgx/encl.c | 265 +++++++++++++++++-
arch/x86/kernel/cpu/sgx/encl.h | 38 +++
arch/x86/kernel/cpu/sgx/main.c | 92 ++++--
arch/x86/kernel/cpu/sgx/reclaim.c | 371 ++++++++++++++++++++++++-
arch/x86/kernel/cpu/sgx/sgx.h | 18 +-
7 files changed, 820 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
index 958c1dbc02e7..f4a80585a519 100644
--- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
@@ -22,6 +22,51 @@ struct sgx_add_page_req {
struct list_head list;
};

+static int sgx_encl_grow(struct sgx_encl *encl)
+{
+ struct sgx_va_page *va_page;
+ int ret;
+
+ BUILD_BUG_ON(SGX_VA_SLOT_COUNT !=
+ (SGX_ENCL_PAGE_VA_OFFSET_MASK >> 3) + 1);
+
+ mutex_lock(&encl->lock);
+ if (encl->flags & SGX_ENCL_DEAD) {
+ mutex_unlock(&encl->lock);
+ return -EFAULT;
+ }
+
+ if (!(encl->page_cnt % SGX_VA_SLOT_COUNT)) {
+ mutex_unlock(&encl->lock);
+
+ va_page = kzalloc(sizeof(*va_page), GFP_KERNEL);
+ if (!va_page)
+ return -ENOMEM;
+ va_page->epc_page = sgx_alloc_va_page();
+ if (IS_ERR(va_page->epc_page)) {
+ ret = PTR_ERR(va_page->epc_page);
+ kfree(va_page);
+ return ret;
+ }
+
+ mutex_lock(&encl->lock);
+ if (encl->flags & SGX_ENCL_DEAD) {
+ sgx_free_page(va_page->epc_page);
+ kfree(va_page);
+ mutex_unlock(&encl->lock);
+ return -EFAULT;
+ } else if (encl->page_cnt % SGX_VA_SLOT_COUNT) {
+ sgx_free_page(va_page->epc_page);
+ kfree(va_page);
+ } else {
+ list_add(&va_page->list, &encl->va_pages);
+ }
+ }
+ encl->page_cnt++;
+ mutex_unlock(&encl->lock);
+ return 0;
+}
+
static bool sgx_process_add_page_req(struct sgx_add_page_req *req,
struct sgx_epc_page *epc_page)
{
@@ -80,6 +125,7 @@ static bool sgx_process_add_page_req(struct sgx_add_page_req *req,
encl_page->encl = encl;
encl_page->epc_page = epc_page;
encl->secs_child_cnt++;
+ sgx_mark_page_reclaimable(encl_page->epc_page);

return true;
}
@@ -110,7 +156,7 @@ static void sgx_add_page_worker(struct work_struct *work)
if (skip_rest)
goto next;

- epc_page = sgx_alloc_page();
+ epc_page = sgx_alloc_page(req->encl_page, true);

mutex_lock(&encl->lock);

@@ -223,6 +269,10 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)
struct file *backing;
long ret;

+ ret = sgx_encl_grow(encl);
+ if (ret)
+ return ret;
+
mutex_lock(&encl->lock);

if (encl->flags & SGX_ENCL_CREATED) {
@@ -247,7 +297,7 @@ static int sgx_encl_create(struct sgx_encl *encl, struct sgx_secs *secs)

INIT_WORK(&encl->work, sgx_add_page_worker);

- secs_epc = sgx_alloc_page();
+ secs_epc = sgx_alloc_page(&encl->secs, true);
if (IS_ERR(secs_epc)) {
ret = PTR_ERR(secs_epc);
goto err_out;
@@ -460,6 +510,10 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr,
return ret;
}

+ ret = sgx_encl_grow(encl);
+ if (ret)
+ return ret;
+
mutex_lock(&encl->lock);

if (!(encl->flags & SGX_ENCL_CREATED) ||
diff --git a/arch/x86/kernel/cpu/sgx/driver/main.c b/arch/x86/kernel/cpu/sgx/driver/main.c
index 5defd1ed3de5..bb7f1932529f 100644
--- a/arch/x86/kernel/cpu/sgx/driver/main.c
+++ b/arch/x86/kernel/cpu/sgx/driver/main.c
@@ -33,6 +33,7 @@ static int sgx_open(struct inode *inode, struct file *file)

kref_init(&encl->refcount);
INIT_LIST_HEAD(&encl->add_page_reqs);
+ INIT_LIST_HEAD(&encl->va_pages);
INIT_RADIX_TREE(&encl->page_tree, GFP_KERNEL);
mutex_init(&encl->lock);
INIT_LIST_HEAD(&encl->mm_list);
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 1a2f2a500634..6bde020e8cfa 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -9,11 +9,91 @@
#include <linux/sched/mm.h>
#include "arch.h"
#include "encl.h"
+#include "encls.h"
#include "sgx.h"

+static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
+ struct sgx_epc_page *epc_page)
+{
+ unsigned long addr = SGX_ENCL_PAGE_ADDR(encl_page);
+ unsigned long va_offset = SGX_ENCL_PAGE_VA_OFFSET(encl_page);
+ struct sgx_encl *encl = encl_page->encl;
+ pgoff_t page_index = sgx_encl_get_index(encl, encl_page);
+ pgoff_t pcmd_index = sgx_pcmd_index(encl, page_index);
+ unsigned long pcmd_offset = sgx_pcmd_offset(page_index);
+ struct sgx_pageinfo pginfo;
+ struct page *backing;
+ struct page *pcmd;
+ int ret;
+
+ backing = sgx_encl_get_backing_page(encl, page_index);
+ if (IS_ERR(backing)) {
+ ret = PTR_ERR(backing);
+ goto err_backing;
+ }
+
+ pcmd = sgx_encl_get_backing_page(encl, pcmd_index);
+ if (IS_ERR(pcmd)) {
+ ret = PTR_ERR(pcmd);
+ goto err_pcmd;
+ }
+
+ pginfo.addr = addr;
+ pginfo.contents = (unsigned long)kmap_atomic(backing);
+ pginfo.metadata = (unsigned long)kmap_atomic(pcmd) + pcmd_offset;
+ pginfo.secs = addr ? (unsigned long)sgx_epc_addr(encl->secs.epc_page) :
+ 0;
+
+ ret = __eldu(&pginfo, sgx_epc_addr(epc_page),
+ sgx_epc_addr(encl_page->va_page->epc_page) + va_offset);
+ if (ret) {
+ if (encls_failed(ret) || encls_returned_code(ret))
+ ENCLS_WARN(ret, "ELDU");
+
+ ret = -EFAULT;
+ }
+
+ kunmap_atomic((void *)(unsigned long)(pginfo.metadata - pcmd_offset));
+ kunmap_atomic((void *)(unsigned long)pginfo.contents);
+
+ put_page(pcmd);
+
+err_pcmd:
+ put_page(backing);
+
+err_backing:
+ return ret;
+}
+
+static struct sgx_epc_page *sgx_encl_eldu(struct sgx_encl_page *encl_page)
+{
+ unsigned long va_offset = SGX_ENCL_PAGE_VA_OFFSET(encl_page);
+ struct sgx_encl *encl = encl_page->encl;
+ struct sgx_epc_page *epc_page;
+ int ret;
+
+ epc_page = sgx_alloc_page(encl_page, false);
+ if (IS_ERR(epc_page))
+ return epc_page;
+
+ ret = __sgx_encl_eldu(encl_page, epc_page);
+ if (ret) {
+ sgx_free_page(epc_page);
+ return ERR_PTR(ret);
+ }
+
+ sgx_free_va_slot(encl_page->va_page, va_offset);
+ list_move(&encl_page->va_page->list, &encl->va_pages);
+ encl_page->desc &= ~SGX_ENCL_PAGE_VA_OFFSET_MASK;
+ encl_page->epc_page = epc_page;
+
+ return epc_page;
+}
+
static struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
unsigned long addr)
{
+ struct sgx_epc_page *epc_page;
struct sgx_encl_page *entry;

/* If process was forked, VMA is still there but vm_private_data is set
@@ -31,10 +111,27 @@ static struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
return ERR_PTR(-EFAULT);

/* Page is already resident in the EPC. */
- if (entry->epc_page)
+ if (entry->epc_page) {
+ if (entry->desc & SGX_ENCL_PAGE_RECLAIMED)
+ return ERR_PTR(-EBUSY);
+
return entry;
+ }

- return ERR_PTR(-EFAULT);
+ if (!(encl->secs.epc_page)) {
+ epc_page = sgx_encl_eldu(&encl->secs);
+ if (IS_ERR(epc_page))
+ return ERR_CAST(epc_page);
+ }
+
+ epc_page = entry->epc_page ? entry->epc_page : sgx_encl_eldu(entry);
+ if (IS_ERR(epc_page))
+ return ERR_CAST(epc_page);
+
+ encl->secs_child_cnt++;
+ sgx_mark_page_reclaimable(entry->epc_page);
+
+ return entry;
}

static void sgx_encl_mm_release_deferred(struct rcu_head *rcu)
@@ -184,6 +281,8 @@ static unsigned int sgx_vma_fault(struct vm_fault *vmf)
goto out;
}

+ sgx_encl_test_and_clear_young(vma->vm_mm, entry);
+
out:
mutex_unlock(&encl->lock);
return ret;
@@ -281,6 +380,7 @@ int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
*/
void sgx_encl_destroy(struct sgx_encl *encl)
{
+ struct sgx_va_page *va_page;
struct sgx_encl_page *entry;
struct radix_tree_iter iter;
void **slot;
@@ -305,6 +405,15 @@ void sgx_encl_destroy(struct sgx_encl *encl)
sgx_free_page(encl->secs.epc_page);
encl->secs.epc_page = NULL;
}
+
+
+ while (!list_empty(&encl->va_pages)) {
+ va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
+ list);
+ list_del(&va_page->list);
+ sgx_free_page(va_page->epc_page);
+ kfree(va_page);
+ }
}

/**
@@ -360,3 +469,155 @@ struct page *sgx_encl_get_backing_page(struct sgx_encl *encl, pgoff_t index)

return shmem_read_mapping_page_gfp(mapping, index, gfpmask);
}
+
+static int sgx_encl_test_and_clear_young_cb(pte_t *ptep, pgtable_t token,
+ unsigned long addr, void *data)
+{
+ pte_t pte;
+ int ret;
+
+ ret = pte_young(*ptep);
+ if (ret) {
+ pte = pte_mkold(*ptep);
+ set_pte_at((struct mm_struct *)data, addr, ptep, pte);
+ }
+
+ return ret;
+}
+
+/**
+ * sgx_encl_test_and_clear_young() - Test and reset the accessed bit
+ * @mm: mm_struct that is checked
+ * @page: enclave page to be tested for recent access
+ *
+ * Checks the Access (A) bit from the PTE corresponding to the enclave page and
+ * clears it.
+ *
+ * Return: 1 if the page has been recently accessed and 0 if not.
+ */
+int sgx_encl_test_and_clear_young(struct mm_struct *mm,
+ struct sgx_encl_page *page)
+{
+ unsigned long addr = SGX_ENCL_PAGE_ADDR(page);
+ struct sgx_encl *encl = page->encl;
+ struct vm_area_struct *vma;
+ int ret;
+
+ ret = sgx_encl_find(mm, addr, &vma);
+ if (ret)
+ return 0;
+
+ if (encl != vma->vm_private_data)
+ return 0;
+
+ ret = apply_to_page_range(vma->vm_mm, addr, PAGE_SIZE,
+ sgx_encl_test_and_clear_young_cb, vma->vm_mm);
+ if (ret < 0)
+ return 0;
+
+ return ret;
+}
+
+/**
+ * sgx_encl_reserve_page() - Reserve an enclave page
+ * @encl: an enclave
+ * @addr: a page address
+ *
+ * Load an enclave page and lock the enclave so that the page can be used by
+ * EDBG* and EMOD*.
+ *
+ * Return:
+ * an enclave page on success
+ * -EFAULT if the load fails
+ */
+struct sgx_encl_page *sgx_encl_reserve_page(struct sgx_encl *encl,
+ unsigned long addr)
+{
+ struct sgx_encl_page *entry;
+
+ for ( ; ; ) {
+ mutex_lock(&encl->lock);
+
+ entry = sgx_encl_load_page(encl, addr);
+ if (PTR_ERR(entry) != -EBUSY)
+ break;
+
+ mutex_unlock(&encl->lock);
+ }
+
+ if (IS_ERR(entry))
+ mutex_unlock(&encl->lock);
+
+ return entry;
+}
+
+/**
+ * sgx_alloc_page - allocate a VA page
+ *
+ * Allocates an &sgx_epc_page instance and converts it to a VA page.
+ *
+ * Return:
+ * a &struct sgx_va_page instance,
+ * -errno otherwise
+ */
+struct sgx_epc_page *sgx_alloc_va_page(void)
+{
+ struct sgx_epc_page *epc_page;
+ int ret;
+
+ epc_page = sgx_alloc_page(NULL, true);
+ if (IS_ERR(epc_page))
+ return ERR_CAST(epc_page);
+
+ ret = __epa(sgx_epc_addr(epc_page));
+ if (ret) {
+ WARN_ONCE(1, "sgx: EPA returned %d (0x%x)", ret, ret);
+ sgx_free_page(epc_page);
+ return ERR_PTR(-EFAULT);
+ }
+
+ return epc_page;
+}
+
+/**
+ * sgx_alloc_va_slot - allocate a VA slot
+ * @va_page: a &struct sgx_va_page instance
+ *
+ * Allocates a slot from a &struct sgx_va_page instance.
+ *
+ * Return: offset of the slot inside the VA page
+ */
+unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page)
+{
+ int slot = find_first_zero_bit(va_page->slots, SGX_VA_SLOT_COUNT);
+
+ if (slot < SGX_VA_SLOT_COUNT)
+ set_bit(slot, va_page->slots);
+
+ return slot << 3;
+}
+
+/**
+ * sgx_free_va_slot - free a VA slot
+ * @va_page: a &struct sgx_va_page instance
+ * @offset: offset of the slot inside the VA page
+ *
+ * Frees a slot from a &struct sgx_va_page instance.
+ */
+void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset)
+{
+ clear_bit(offset >> 3, va_page->slots);
+}
+
+/**
+ * sgx_va_page_full - is the VA page full?
+ * @va_page: a &struct sgx_va_page instance
+ *
+ * Return: true if all slots have been taken
+ */
+bool sgx_va_page_full(struct sgx_va_page *va_page)
+{
+ int slot = find_first_zero_bit(va_page->slots, SGX_VA_SLOT_COUNT);
+
+ return slot == SGX_VA_SLOT_COUNT;
+}
diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
index 3a186e56f54a..379fe4c22b5d 100644
--- a/arch/x86/kernel/cpu/sgx/encl.h
+++ b/arch/x86/kernel/cpu/sgx/encl.h
@@ -19,6 +19,10 @@
/**
* enum sgx_encl_page_desc - defines bits for an enclave page's descriptor
* %SGX_ENCL_PAGE_TCS: The page is a TCS page.
+ * %SGX_ENCL_PAGE_RECLAIMED: The page is in the process of being
+ * reclaimed.
+ * %SGX_ENCL_PAGE_VA_OFFSET_MASK: Holds the offset in the Version Array
+ * (VA) page for a swapped page.
* %SGX_ENCL_PAGE_ADDR_MASK: Holds the virtual address of the page.
*
* The page address for SECS is zero and is used by the subsystem to recognize
@@ -27,6 +31,8 @@
enum sgx_encl_page_desc {
SGX_ENCL_PAGE_TCS = BIT(0),
/* Bits 11:3 are available when the page is not swapped. */
+ SGX_ENCL_PAGE_RECLAIMED = BIT(3),
+ SGX_ENCL_PAGE_VA_OFFSET_MASK = GENMASK_ULL(11, 3),
SGX_ENCL_PAGE_ADDR_MASK = PAGE_MASK,
};

@@ -39,6 +45,7 @@ struct sgx_encl_page {
unsigned long desc;
unsigned long vm_prot_bits;
struct sgx_epc_page *epc_page;
+ struct sgx_va_page *va_page;
struct sgx_encl *encl;
};

@@ -72,6 +79,7 @@ struct sgx_encl {
unsigned long base;
unsigned long size;
unsigned long ssaframesize;
+ struct list_head va_pages;
struct radix_tree_root page_tree;
struct list_head add_page_reqs;
struct work_struct work;
@@ -79,8 +87,28 @@ struct sgx_encl {
cpumask_t cpumask;
};

+#define SGX_VA_SLOT_COUNT 512
+
+struct sgx_va_page {
+ struct sgx_epc_page *epc_page;
+ DECLARE_BITMAP(slots, SGX_VA_SLOT_COUNT);
+ struct list_head list;
+};
+
extern const struct vm_operations_struct sgx_vm_ops;

+static inline pgoff_t sgx_pcmd_index(struct sgx_encl *encl,
+ pgoff_t page_index)
+{
+ return PFN_DOWN(encl->size) + 1 + (page_index >> 5);
+}
+
+static inline unsigned long sgx_pcmd_offset(pgoff_t page_index)
+{
+ return (page_index & (PAGE_SIZE / sizeof(struct sgx_pcmd) - 1)) *
+ sizeof(struct sgx_pcmd);
+}
+
enum sgx_encl_mm_iter {
SGX_ENCL_MM_ITER_DONE = 0,
SGX_ENCL_MM_ITER_NEXT = 1,
@@ -94,7 +122,17 @@ void sgx_encl_release(struct kref *ref);
pgoff_t sgx_encl_get_index(struct sgx_encl *encl, struct sgx_encl_page *page);
struct page *sgx_encl_get_backing_page(struct sgx_encl *encl, pgoff_t index);
int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm);
+int sgx_encl_test_and_clear_young(struct mm_struct *mm,
+ struct sgx_encl_page *page);
+struct sgx_encl_page *sgx_encl_reserve_page(struct sgx_encl *encl,
+ unsigned long addr);
+
+struct sgx_epc_page *sgx_alloc_va_page(void);
+unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page);
+void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset);
+bool sgx_va_page_full(struct sgx_va_page *va_page);

int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
unsigned long end, unsigned long vm_prot_bits);
+
#endif /* _X86_ENCL_H */
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 9d5871f3f5dd..f790a03571c5 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -19,7 +19,7 @@ int sgx_nr_epc_sections;
/* A per-cpu cache for the last known values of IA32_SGXLEPUBKEYHASHx MSRs. */
static DEFINE_PER_CPU(u64 [4], sgx_lepubkeyhash_cache);

-static struct sgx_epc_page *sgx_section_get_page(
+static struct sgx_epc_page *sgx_section_try_take_page(
struct sgx_epc_section *section)
{
struct sgx_epc_page *page;
@@ -27,23 +27,14 @@ static struct sgx_epc_page *sgx_section_get_page(
if (!section->free_cnt)
return NULL;

- page = list_first_entry(&section->page_list,
- struct sgx_epc_page, list);
+ page = list_first_entry(&section->page_list, struct sgx_epc_page,
+ list);
list_del_init(&page->list);
section->free_cnt--;
return page;
}

-/**
- * sgx_alloc_page - Allocate an EPC page
- *
- * Try to grab a page from the free EPC page list.
- *
- * Return:
- * a pointer to a &struct sgx_epc_page instance,
- * -errno on error
- */
-struct sgx_epc_page *sgx_alloc_page(void)
+static struct sgx_epc_page *sgx_try_alloc_page(void *owner)
{
struct sgx_epc_section *section;
struct sgx_epc_page *page;
@@ -52,24 +43,73 @@ struct sgx_epc_page *sgx_alloc_page(void)
for (i = 0; i < sgx_nr_epc_sections; i++) {
section = &sgx_epc_sections[i];
spin_lock(&section->lock);
- page = sgx_section_get_page(section);
+ page = sgx_section_try_take_page(section);
spin_unlock(&section->lock);

- if (page)
+ if (page) {
+ page->owner = owner;
return page;
+ }
}

- return ERR_PTR(-ENOMEM);
+ return NULL;
+}
+
+/**
+ * sgx_alloc_page - Allocate an EPC page
+ * @owner: the owner of the EPC page
+ * @reclaim: reclaim pages if necessary
+ *
+ * Try to grab a page from the free EPC page list. If there is a free page
+ * available, it is returned to the caller. The @reclaim parameter hints
+ * the EPC memory manager to swap pages when required.
+ *
+ * Return:
+ * a pointer to a &struct sgx_epc_page instance,
+ * -errno on error
+ */
+struct sgx_epc_page *sgx_alloc_page(void *owner, bool reclaim)
+{
+ struct sgx_epc_page *entry;
+
+ for ( ; ; ) {
+ entry = sgx_try_alloc_page(owner);
+ if (entry)
+ break;
+
+ if (list_empty(&sgx_active_page_list))
+ return ERR_PTR(-ENOMEM);
+
+ if (!reclaim) {
+ entry = ERR_PTR(-EBUSY);
+ break;
+ }
+
+ if (signal_pending(current)) {
+ entry = ERR_PTR(-ERESTARTSYS);
+ break;
+ }
+
+ sgx_reclaim_pages();
+ schedule();
+ }
+
+ if (sgx_calc_free_cnt() < SGX_NR_LOW_PAGES)
+ wake_up(&ksgxswapd_waitq);
+
+ return entry;
}

/**
* __sgx_free_page - Free an EPC page
* @page: pointer a previously allocated EPC page
*
- * EREMOVE an EPC page and insert it back to the list of free pages.
+ * EREMOVE an EPC page and insert it back to the list of free pages. If the
+ * page is reclaimable, delete it from the active page list.
*
* Return:
* 0 on success
+ * -EBUSY if the page cannot be removed from the active list
* SGX error code if EREMOVE fails
*/
int __sgx_free_page(struct sgx_epc_page *page)
@@ -77,6 +117,23 @@ int __sgx_free_page(struct sgx_epc_page *page)
struct sgx_epc_section *section = sgx_epc_section(page);
int ret;

+ /*
+ * Remove the page from the active list if necessary. If the page
+ * is actively being reclaimed, i.e. RECLAIMABLE is set but the
+ * page isn't on the active list, return -EBUSY as we can't free
+ * the page at this time since it is "owned" by the reclaimer.
+ */
+ spin_lock(&sgx_active_page_list_lock);
+ if (page->desc & SGX_EPC_PAGE_RECLAIMABLE) {
+ if (list_empty(&page->list)) {
+ spin_unlock(&sgx_active_page_list_lock);
+ return -EBUSY;
+ }
+ list_del(&page->list);
+ page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
+ }
+ spin_unlock(&sgx_active_page_list_lock);
+
ret = __eremove(sgx_epc_addr(page));
if (ret)
return ret;
@@ -102,6 +159,7 @@ void sgx_free_page(struct sgx_epc_page *page)
int ret;

ret = __sgx_free_page(page);
+ WARN(ret < 0, "sgx: cannot free page, reclaim in-progress");
WARN(ret > 0, "sgx: EREMOVE returned %d (0x%x)", ret, ret);
}

diff --git a/arch/x86/kernel/cpu/sgx/reclaim.c b/arch/x86/kernel/cpu/sgx/reclaim.c
index 62a9233330f9..e9427220415b 100644
--- a/arch/x86/kernel/cpu/sgx/reclaim.c
+++ b/arch/x86/kernel/cpu/sgx/reclaim.c
@@ -9,10 +9,13 @@
#include <linux/slab.h>
#include <linux/sched/mm.h>
#include <linux/sched/signal.h>
-#include "encls.h"
+#include "driver/driver.h"
#include "sgx.h"

struct task_struct *ksgxswapd_tsk;
+DECLARE_WAIT_QUEUE_HEAD(ksgxswapd_waitq);
+LIST_HEAD(sgx_active_page_list);
+DEFINE_SPINLOCK(sgx_active_page_list_lock);

static void sgx_sanitize_section(struct sgx_epc_section *section)
{
@@ -58,6 +61,12 @@ static void sgx_sanitize_section(struct sgx_epc_section *section)
}
}

+static inline bool sgx_should_reclaim(void)
+{
+ return sgx_calc_free_cnt() < SGX_NR_HIGH_PAGES &&
+ !list_empty(&sgx_active_page_list);
+}
+
static int ksgxswapd(void *p)
{
int i;
@@ -67,6 +76,19 @@ static int ksgxswapd(void *p)
for (i = 0; i < sgx_nr_epc_sections; i++)
sgx_sanitize_section(&sgx_epc_sections[i]);

+ while (!kthread_should_stop()) {
+ if (try_to_freeze())
+ continue;
+
+ wait_event_freezable(ksgxswapd_waitq, kthread_should_stop() ||
+ sgx_should_reclaim());
+
+ if (sgx_should_reclaim())
+ sgx_reclaim_pages();
+
+ cond_resched();
+ }
+
return 0;
}

@@ -82,3 +104,350 @@ int sgx_page_reclaimer_init(void)

return 0;
}
+
+/**
+ * sgx_mark_page_reclaimable() - Mark a page as reclaimable
+ * @page: EPC page
+ *
+ * Mark a page as reclaimable and add it to the active page list. Pages
+ * are automatically removed from the active list when freed.
+ */
+void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
+{
+ spin_lock(&sgx_active_page_list_lock);
+ page->desc |= SGX_EPC_PAGE_RECLAIMABLE;
+ list_add_tail(&page->list, &sgx_active_page_list);
+ spin_unlock(&sgx_active_page_list_lock);
+}
+
+bool sgx_reclaimer_get(struct sgx_epc_page *epc_page)
+{
+ struct sgx_encl_page *encl_page = epc_page->owner;
+ struct sgx_encl *encl = encl_page->encl;
+
+ return kref_get_unless_zero(&encl->refcount) != 0;
+}
+
+void sgx_reclaimer_put(struct sgx_epc_page *epc_page)
+{
+ struct sgx_encl_page *encl_page = epc_page->owner;
+ struct sgx_encl *encl = encl_page->encl;
+
+ kref_put(&encl->refcount, sgx_encl_release);
+}
+
+static bool sgx_reclaimer_evict(struct sgx_epc_page *epc_page)
+{
+ struct sgx_encl_page *page = epc_page->owner;
+ struct sgx_encl *encl = page->encl;
+ struct sgx_encl_mm *encl_mm;
+ bool ret = true;
+ int idx;
+
+ idx = srcu_read_lock(&encl->srcu);
+
+ list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+ if (!mmget_not_zero(encl_mm->mm))
+ continue;
+
+ down_read(&encl_mm->mm->mmap_sem);
+ ret = !sgx_encl_test_and_clear_young(encl_mm->mm, page);
+ up_read(&encl_mm->mm->mmap_sem);
+
+ mmput_async(encl_mm->mm);
+
+ if (!ret || (encl->flags & SGX_ENCL_DEAD))
+ break;
+ }
+
+ srcu_read_unlock(&encl->srcu, idx);
+
+ /*
+ * Do not reclaim this page if it has been recently accessed by any
+ * mm_struct *and* if the enclave is still alive. No need to take
+ * the enclave's lock, worst case scenario reclaiming pages from a
+ * dead enclave is delayed slightly. A live enclave with a recently
+ * accessed page is more common and avoiding lock contention in that
+ * case is a boon to performance.
+ */
+ if (!ret && !(encl->flags & SGX_ENCL_DEAD))
+ return false;
+
+ mutex_lock(&encl->lock);
+ page->desc |= SGX_ENCL_PAGE_RECLAIMED;
+ mutex_unlock(&encl->lock);
+
+ return true;
+}
+
+static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
+{
+ struct sgx_encl_page *page = epc_page->owner;
+ unsigned long addr = SGX_ENCL_PAGE_ADDR(page);
+ struct sgx_encl *encl = page->encl;
+ struct sgx_encl_mm *encl_mm;
+ struct vm_area_struct *vma;
+ int idx, ret;
+
+ idx = srcu_read_lock(&encl->srcu);
+
+ list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+ if (!mmget_not_zero(encl_mm->mm))
+ continue;
+
+ down_read(&encl_mm->mm->mmap_sem);
+
+ ret = sgx_encl_find(encl_mm->mm, addr, &vma);
+ if (!ret && encl == vma->vm_private_data)
+ zap_vma_ptes(vma, addr, PAGE_SIZE);
+
+ up_read(&encl_mm->mm->mmap_sem);
+
+ mmput_async(encl_mm->mm);
+ }
+
+ srcu_read_unlock(&encl->srcu, idx);
+
+ mutex_lock(&encl->lock);
+
+ if (!(encl->flags & SGX_ENCL_DEAD)) {
+ ret = __eblock(sgx_epc_addr(epc_page));
+ if (encls_failed(ret))
+ ENCLS_WARN(ret, "EBLOCK");
+ }
+
+ mutex_unlock(&encl->lock);
+}
+
+static int __sgx_encl_ewb(struct sgx_encl *encl, struct sgx_epc_page *epc_page,
+ struct sgx_va_page *va_page, unsigned int va_offset)
+{
+ struct sgx_encl_page *encl_page = epc_page->owner;
+ pgoff_t page_index = sgx_encl_get_index(encl, encl_page);
+ pgoff_t pcmd_index = sgx_pcmd_index(encl, page_index);
+ unsigned long pcmd_offset = sgx_pcmd_offset(page_index);
+ struct sgx_pageinfo pginfo;
+ struct page *backing;
+ struct page *pcmd;
+ int ret;
+
+ backing = sgx_encl_get_backing_page(encl, page_index);
+ if (IS_ERR(backing)) {
+ ret = PTR_ERR(backing);
+ goto err_backing;
+ }
+
+ pcmd = sgx_encl_get_backing_page(encl, pcmd_index);
+ if (IS_ERR(pcmd)) {
+ ret = PTR_ERR(pcmd);
+ goto err_pcmd;
+ }
+
+ pginfo.addr = 0;
+ pginfo.contents = (unsigned long)kmap_atomic(backing);
+ pginfo.metadata = (unsigned long)kmap_atomic(pcmd) + pcmd_offset;
+ pginfo.secs = 0;
+ ret = __ewb(&pginfo, sgx_epc_addr(epc_page),
+ sgx_epc_addr(va_page->epc_page) + va_offset);
+ kunmap_atomic((void *)(unsigned long)(pginfo.metadata - pcmd_offset));
+ kunmap_atomic((void *)(unsigned long)pginfo.contents);
+
+ set_page_dirty(pcmd);
+ put_page(pcmd);
+ set_page_dirty(backing);
+
+err_pcmd:
+ put_page(backing);
+
+err_backing:
+ return ret;
+}
+
+static void sgx_ipi_cb(void *info)
+{
+}
+
+static const cpumask_t *sgx_encl_ewb_cpumask(struct sgx_encl *encl)
+{
+ cpumask_t *cpumask = &encl->cpumask;
+ struct sgx_encl_mm *encl_mm;
+ int idx;
+
+ cpumask_clear(cpumask);
+
+ idx = srcu_read_lock(&encl->srcu);
+
+ list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+ if (!mmget_not_zero(encl_mm->mm))
+ continue;
+
+ cpumask_or(cpumask, cpumask, mm_cpumask(encl_mm->mm));
+
+ mmput_async(encl_mm->mm);
+ }
+
+ srcu_read_unlock(&encl->srcu, idx);
+
+ return cpumask;
+}
+
+static void sgx_encl_ewb(struct sgx_epc_page *epc_page, bool do_free)
+{
+ struct sgx_encl_page *encl_page = epc_page->owner;
+ struct sgx_encl *encl = encl_page->encl;
+ struct sgx_va_page *va_page;
+ unsigned int va_offset;
+ int ret;
+
+ encl_page->desc &= ~SGX_ENCL_PAGE_RECLAIMED;
+
+ if (!(encl->flags & SGX_ENCL_DEAD)) {
+ va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
+ list);
+ va_offset = sgx_alloc_va_slot(va_page);
+ if (sgx_va_page_full(va_page))
+ list_move_tail(&va_page->list, &encl->va_pages);
+
+ ret = __sgx_encl_ewb(encl, epc_page, va_page, va_offset);
+ if (ret == SGX_NOT_TRACKED) {
+ ret = __etrack(sgx_epc_addr(encl->secs.epc_page));
+ if (ret) {
+ if (encls_failed(ret) ||
+ encls_returned_code(ret))
+ ENCLS_WARN(ret, "ETRACK");
+ }
+
+ ret = __sgx_encl_ewb(encl, epc_page, va_page,
+ va_offset);
+ if (ret == SGX_NOT_TRACKED) {
+ /*
+ * Slow path, send IPIs to kick cpus out of the
+ * enclave. Note, it's imperative that the cpu
+ * mask is generated *after* ETRACK, else we'll
+ * miss cpus that entered the enclave between
+ * generating the mask and incrementing epoch.
+ */
+ on_each_cpu_mask(sgx_encl_ewb_cpumask(encl),
+ sgx_ipi_cb, NULL, 1);
+ ret = __sgx_encl_ewb(encl, epc_page, va_page,
+ va_offset);
+ }
+ }
+
+ if (ret)
+ if (encls_failed(ret) || encls_returned_code(ret))
+ ENCLS_WARN(ret, "EWB");
+
+ encl_page->desc |= va_offset;
+ encl_page->va_page = va_page;
+ } else if (!do_free) {
+ ret = __eremove(sgx_epc_addr(epc_page));
+ WARN(ret, "EREMOVE returned %d\n", ret);
+ }
+
+ if (do_free)
+ sgx_free_page(epc_page);
+
+ encl_page->epc_page = NULL;
+}
+
+static void sgx_reclaimer_write(struct sgx_epc_page *epc_page)
+{
+ struct sgx_encl_page *encl_page = epc_page->owner;
+ struct sgx_encl *encl = encl_page->encl;
+
+ mutex_lock(&encl->lock);
+
+ sgx_encl_ewb(epc_page, false);
+ encl->secs_child_cnt--;
+ if (!encl->secs_child_cnt &&
+ (encl->flags & (SGX_ENCL_DEAD | SGX_ENCL_INITIALIZED))) {
+ sgx_encl_ewb(encl->secs.epc_page, true);
+ }
+
+ mutex_unlock(&encl->lock);
+}
+
+/**
+ * sgx_reclaim_pages() - Reclaim EPC pages from the consumers
+ * Takes a fixed chunk of pages from the global list of consumed EPC pages and
+ * tries to swap them. Only the pages that are either being freed by the
+ * consumer or actively used are skipped.
+ */
+void sgx_reclaim_pages(void)
+{
+ struct sgx_epc_page *chunk[SGX_NR_TO_SCAN + 1];
+ struct sgx_epc_page *epc_page;
+ struct sgx_epc_section *section;
+ int i, j;
+
+ spin_lock(&sgx_active_page_list_lock);
+ for (i = 0, j = 0; i < SGX_NR_TO_SCAN; i++) {
+ if (list_empty(&sgx_active_page_list))
+ break;
+
+ epc_page = list_first_entry(&sgx_active_page_list,
+ struct sgx_epc_page, list);
+ list_del_init(&epc_page->list);
+
+ if (sgx_reclaimer_get(epc_page))
+ chunk[j++] = epc_page;
+ else
+ /* The owner is freeing the page. No need to add the
+ * page back to the list of reclaimable pages.
+ */
+ epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
+ }
+ spin_unlock(&sgx_active_page_list_lock);
+
+ for (i = 0; i < j; i++) {
+ epc_page = chunk[i];
+ if (sgx_reclaimer_evict(epc_page))
+ continue;
+
+ sgx_reclaimer_put(epc_page);
+
+ spin_lock(&sgx_active_page_list_lock);
+ list_add_tail(&epc_page->list, &sgx_active_page_list);
+ spin_unlock(&sgx_active_page_list_lock);
+
+ chunk[i] = NULL;
+ }
+
+ for (i = 0; i < j; i++) {
+ epc_page = chunk[i];
+ if (epc_page)
+ sgx_reclaimer_block(epc_page);
+ }
+
+ for (i = 0; i < j; i++) {
+ epc_page = chunk[i];
+ if (epc_page) {
+ sgx_reclaimer_write(epc_page);
+ sgx_reclaimer_put(epc_page);
+ epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
+
+ section = sgx_epc_section(epc_page);
+
+ spin_lock(&section->lock);
+ list_add_tail(&epc_page->list,
+ &section->page_list);
+ section->free_cnt++;
+ spin_unlock(&section->lock);
+ }
+ }
+}
+
+unsigned long sgx_calc_free_cnt(void)
+{
+ struct sgx_epc_section *section;
+ unsigned long free_cnt = 0;
+ int i;
+
+ for (i = 0; i < sgx_nr_epc_sections; i++) {
+ section = &sgx_epc_sections[i];
+ free_cnt += section->free_cnt;
+ }
+
+ return free_cnt;
+}
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index fa37da4c7b63..f0ff7bd3d18e 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -12,6 +12,7 @@

struct sgx_epc_page {
unsigned long desc;
+ struct sgx_encl_page *owner;
struct list_head list;
};

@@ -42,9 +43,14 @@ extern struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
* physical memory. The existing and near-future
* hardware defines at most eight sections, hence
* three bits to hold a section.
+ * %SGX_EPC_PAGE_RECLAIMABLE: The page has been been marked as reclaimable.
+ * Pages need to be colored this way because a page
+ * can be out of the active page list in the
+ * process of being swapped out.
*/
enum sgx_epc_page_desc {
SGX_EPC_SECTION_MASK = GENMASK_ULL(3, 0),
+ SGX_EPC_PAGE_RECLAIMABLE = BIT(4),
/* bits 12-63 are reserved for the physical page address of the page */
};

@@ -60,12 +66,22 @@ static inline void *sgx_epc_addr(struct sgx_epc_page *page)
return section->va + (page->desc & PAGE_MASK) - section->pa;
}

+#define SGX_NR_TO_SCAN 16
+#define SGX_NR_LOW_PAGES 32
+#define SGX_NR_HIGH_PAGES 64
+
extern int sgx_nr_epc_sections;
extern struct task_struct *ksgxswapd_tsk;
+extern struct wait_queue_head(ksgxswapd_waitq);
+extern struct list_head sgx_active_page_list;
+extern spinlock_t sgx_active_page_list_lock;

int sgx_page_reclaimer_init(void);
+void sgx_mark_page_reclaimable(struct sgx_epc_page *page);
+unsigned long sgx_calc_free_cnt(void);
+void sgx_reclaim_pages(void);

-struct sgx_epc_page *sgx_alloc_page(void);
+struct sgx_epc_page *sgx_alloc_page(void *owner, bool reclaim);
int __sgx_free_page(struct sgx_epc_page *page);
void sgx_free_page(struct sgx_epc_page *page);
int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken *token,
--
2.20.1