[RFC PATCH 16/20] x86/sgx: Add EPC OOM path to forcefully reclaim EPC

Kristen Carlson Accardi
2022-09-22T17:13:13Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

Introduce the OOM path for killing an enclave with the reclaimer
is no longer able to reclaim enough EPC pages. Find a victim enclave,
which will be an enclave with EPC pages remaining that are not
accessible to the reclaimer ("unreclaimable"). Once a victim is
identified, mark the enclave as OOM and zap the enclaves entire
page range. Release all the enclaves resources except for the
struct sgx_encl memory itself.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>
---
arch/x86/kernel/cpu/sgx/encl.c | 74 +++++++++++++++---
arch/x86/kernel/cpu/sgx/encl.h | 2 +
arch/x86/kernel/cpu/sgx/main.c | 135 +++++++++++++++++++++++++++++++++
arch/x86/kernel/cpu/sgx/sgx.h | 1 +
4 files changed, 201 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 672b302f3688..fe6f0a62c4f1 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -622,7 +622,8 @@ static int sgx_vma_access(struct vm_area_struct *vma, unsigned long addr,
if (!encl)
return -EFAULT;

- if (!test_bit(SGX_ENCL_DEBUG, &encl->flags))
+ if (!test_bit(SGX_ENCL_DEBUG, &encl->flags) ||
+ test_bit(SGX_ENCL_OOM, &encl->flags))
return -EFAULT;

for (i = 0; i < len; i += cnt) {
@@ -668,16 +669,8 @@ const struct vm_operations_struct sgx_vm_ops = {
.access = sgx_vma_access,
};

-/**
- * sgx_encl_release - Destroy an enclave instance
- * @ref: address of a kref inside &sgx_encl
- *
- * Used together with kref_put(). Frees all the resources associated with the
- * enclave and the instance itself.
- */
-void sgx_encl_release(struct kref *ref)
+static void __sgx_encl_release(struct sgx_encl *encl)
{
- struct sgx_encl *encl = container_of(ref, struct sgx_encl, refcount);
struct sgx_va_page *va_page;
struct sgx_encl_page *entry;
unsigned long index;
@@ -712,7 +705,7 @@ void sgx_encl_release(struct kref *ref)
while (!list_empty(&encl->va_pages)) {
va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
list);
- list_del(&va_page->list);
+ list_del_init(&va_page->list);
sgx_drop_epc_page(va_page->epc_page);
sgx_encl_free_epc_page(va_page->epc_page);
kfree(va_page);
@@ -728,10 +721,66 @@ void sgx_encl_release(struct kref *ref)
/* Detect EPC page leak's. */
WARN_ON_ONCE(encl->secs_child_cnt);
WARN_ON_ONCE(encl->secs.epc_page);
+}
+
+/**
+ * sgx_encl_release - Destroy an enclave instance
+ * @ref: address of a kref inside &sgx_encl
+ *
+ * Used together with kref_put(). Frees all the resources associated with the
+ * enclave and the instance itself.
+ */
+void sgx_encl_release(struct kref *ref)
+{
+ struct sgx_encl *encl = container_of(ref, struct sgx_encl, refcount);
+
+ /* if the enclave was OOM killed previously, it just needs to be freed */
+ if (!test_bit(SGX_ENCL_OOM, &encl->flags))
+ __sgx_encl_release(encl);

kfree(encl);
}

+/**
+ * sgx_encl_destroy - prepare the enclave for release
+ * @encl: address of the sgx_encl to drain
+ *
+ * Used during oom kill to empty the mm_list entries after they have
+ * been zapped. Release the remaining enclave resources without freeing
+ * struct sgx_encl.
+ */
+void sgx_encl_destroy(struct sgx_encl *encl)
+{
+ struct sgx_encl_mm *encl_mm;
+
+ for ( ; ; ) {
+ spin_lock(&encl->mm_lock);
+
+ if (list_empty(&encl->mm_list)) {
+ encl_mm = NULL;
+ } else {
+ encl_mm = list_first_entry(&encl->mm_list,
+ struct sgx_encl_mm, list);
+ list_del_rcu(&encl_mm->list);
+ }
+
+ spin_unlock(&encl->mm_lock);
+
+ /* The enclave is no longer mapped by any mm. */
+ if (!encl_mm)
+ break;
+
+ synchronize_srcu(&encl->srcu);
+ mmu_notifier_unregister(&encl_mm->mmu_notifier, encl_mm->mm);
+ kfree(encl_mm);
+
+ /* 'encl_mm' is gone, put encl_mm->encl reference: */
+ kref_put(&encl->refcount, sgx_encl_release);
+ }
+
+ __sgx_encl_release(encl);
+}
+
/*
* 'mm' is exiting and no longer needs mmu notifications.
*/
@@ -801,6 +850,9 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm)
struct sgx_encl_mm *encl_mm;
int ret;

+ if (test_bit(SGX_ENCL_OOM, &encl->flags))
+ return -ENOMEM;
+
/*
* Even though a single enclave may be mapped into an mm more than once,
* each 'mm' only appears once on encl->mm_list. This is guaranteed by
diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
index 831d63f80f5a..f4935632e53a 100644
--- a/arch/x86/kernel/cpu/sgx/encl.h
+++ b/arch/x86/kernel/cpu/sgx/encl.h
@@ -39,6 +39,7 @@ enum sgx_encl_flags {
SGX_ENCL_DEBUG = BIT(1),
SGX_ENCL_CREATED = BIT(2),
SGX_ENCL_INITIALIZED = BIT(3),
+ SGX_ENCL_OOM = BIT(4),
};

struct sgx_encl_mm {
@@ -125,5 +126,6 @@ struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
unsigned long addr);
struct sgx_va_page *sgx_encl_grow(struct sgx_encl *encl, bool reclaim);
void sgx_encl_shrink(struct sgx_encl *encl, struct sgx_va_page *va_page);
+void sgx_encl_destroy(struct sgx_encl *encl);

#endif /* _X86_ENCL_H */
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 151ad720a4ec..082c08228840 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -657,6 +657,141 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
atomic_long_inc(&sgx_nr_free_pages);
}

+static bool sgx_oom_get_ref(struct sgx_epc_page *epc_page)
+{
+ struct sgx_encl *encl;
+
+ if (epc_page->flags & SGX_EPC_PAGE_ENCLAVE)
+ encl = ((struct sgx_encl_page *)epc_page->owner)->encl;
+ else if (epc_page->flags & SGX_EPC_PAGE_VERSION_ARRAY)
+ encl = epc_page->owner;
+ else
+ return false;
+
+ return kref_get_unless_zero(&encl->refcount);
+}
+
+static struct sgx_epc_page *sgx_oom_get_victim(struct sgx_epc_lru *lru)
+{
+ struct sgx_epc_page *epc_page, *tmp;
+
+ if (list_empty(&lru->unreclaimable))
+ return NULL;
+
+ list_for_each_entry_safe(epc_page, tmp, &lru->unreclaimable, list) {
+ list_del_init(&epc_page->list);
+
+ if (sgx_oom_get_ref(epc_page))
+ return epc_page;
+ }
+ return NULL;
+}
+
+static void sgx_epc_oom_zap(void *owner, struct mm_struct *mm, unsigned long start,
+ unsigned long end, const struct vm_operations_struct *ops)
+{
+ struct vm_area_struct *vma, *tmp;
+ unsigned long vm_end;
+
+ vma = find_vma(mm, start);
+ if (!vma || vma->vm_ops != ops || vma->vm_private_data != owner ||
+ vma->vm_start >= end)
+ return;
+
+ for (tmp = vma; tmp->vm_start < end; tmp = tmp->vm_next) {
+ do {
+ vm_end = tmp->vm_end;
+ tmp = tmp->vm_next;
+ } while (tmp && tmp->vm_ops == ops &&
+ vma->vm_private_data == owner && tmp->vm_start < end);
+
+ zap_page_range(vma, vma->vm_start, vm_end - vma->vm_start);
+
+ if (!tmp)
+ break;
+ }
+}
+
+static void sgx_oom_encl(struct sgx_encl *encl)
+{
+ unsigned long mm_list_version;
+ struct sgx_encl_mm *encl_mm;
+ int idx;
+
+ set_bit(SGX_ENCL_OOM, &encl->flags);
+
+ if (!test_bit(SGX_ENCL_CREATED, &encl->flags))
+ goto out;
+
+ do {
+ mm_list_version = encl->mm_list_version;
+
+ /* Pairs with smp_rmb() in sgx_encl_mm_add(). */
+ smp_rmb();
+
+ 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;
+
+ mmap_read_lock(encl_mm->mm);
+
+ sgx_epc_oom_zap(encl, encl_mm->mm, encl->base,
+ encl->base + encl->size, &sgx_vm_ops);
+
+ mmap_read_unlock(encl_mm->mm);
+
+ mmput_async(encl_mm->mm);
+ }
+
+ srcu_read_unlock(&encl->srcu, idx);
+ } while (WARN_ON_ONCE(encl->mm_list_version != mm_list_version));
+
+ mutex_lock(&encl->lock);
+ sgx_encl_destroy(encl);
+ mutex_unlock(&encl->lock);
+
+out:
+ /*
+ * This puts the refcount we took when we identified this enclave as
+ * an OOM victim.
+ */
+ kref_put(&encl->refcount, sgx_encl_release);
+}
+
+static inline void sgx_oom_encl_page(struct sgx_encl_page *encl_page)
+{
+ return sgx_oom_encl(encl_page->encl);
+}
+
+/**
+ * sgx_epc_oom() - invoke EPC out-of-memory handling on target LRU
+ * @lru: LRU that is low
+ *
+ * Return: %true if a victim was found and kicked.
+ */
+bool sgx_epc_oom(struct sgx_epc_lru *lru)
+{
+ struct sgx_epc_page *victim;
+
+ spin_lock(&lru->lock);
+ victim = sgx_oom_get_victim(lru);
+ spin_unlock(&lru->lock);
+
+ if (!victim)
+ return false;
+
+ if (victim->flags & SGX_EPC_PAGE_ENCLAVE)
+ sgx_oom_encl_page(victim->owner);
+ else if (victim->flags & SGX_EPC_PAGE_VERSION_ARRAY)
+ sgx_oom_encl(victim->owner);
+ else
+ WARN_ON_ONCE(1);
+
+ return true;
+}
+
static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
unsigned long index,
struct sgx_epc_section *section)
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 0598d534371b..a4c7ee0a4958 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -116,6 +116,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim);
int sgx_reclaim_epc_pages(int nr_to_scan, bool ignore_age);
void sgx_isolate_epc_pages(struct sgx_epc_lru *lru, int *nr_to_scan,
struct list_head *dst);
+bool sgx_epc_oom(struct sgx_epc_lru *lru);

void sgx_ipi_cb(void *info);

--
2.37.3