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A single fix for x86/SGX to prevent that memory which is allocated for an

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SGX enclave is accounted to the wrong memory control group.
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Merge tag 'x86-urgent-2022-06-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 SGX fix from Thomas Gleixner:
 "A single fix for x86/SGX to prevent that memory which is allocated for
  an SGX enclave is accounted to the wrong memory control group"

* tag 'x86-urgent-2022-06-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/sgx: Set active memcg prior to shmem allocation
This commit is contained in:
Linus Torvalds 2022-06-05 11:00:43 -07:00
commit d717180e7f
3 changed files with 115 additions and 6 deletions
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105
arch/x86/kernel/cpu/sgx/encl.c
View File

@ -152,7 +152,7 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
page_pcmd_off = sgx_encl_get_backing_page_pcmd_offset(encl, page_index);
ret = sgx_encl_get_backing(encl, page_index, &b);
ret = sgx_encl_lookup_backing(encl, page_index, &b);
if (ret)
return ret;
@ -718,7 +718,7 @@ static struct page *sgx_encl_get_backing_page(struct sgx_encl *encl,
* 0 on success,
* -errno otherwise.
*/
int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long page_index,
static int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long page_index,
struct sgx_backing *backing)
{
pgoff_t page_pcmd_off = sgx_encl_get_backing_page_pcmd_offset(encl, page_index);
@ -743,6 +743,107 @@ int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long page_index,
return 0;
}
/*
* When called from ksgxd, returns the mem_cgroup of a struct mm stored
* in the enclave's mm_list. When not called from ksgxd, just returns
* the mem_cgroup of the current task.
*/
static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl)
{
struct mem_cgroup *memcg = NULL;
struct sgx_encl_mm *encl_mm;
int idx;
/*
* If called from normal task context, return the mem_cgroup
* of the current task's mm. The remainder of the handling is for
* ksgxd.
*/
if (!current_is_ksgxd())
return get_mem_cgroup_from_mm(current->mm);
/*
* Search the enclave's mm_list to find an mm associated with
* this enclave to charge the allocation to.
*/
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;
memcg = get_mem_cgroup_from_mm(encl_mm->mm);
mmput_async(encl_mm->mm);
break;
}
srcu_read_unlock(&encl->srcu, idx);
/*
* In the rare case that there isn't an mm associated with
* the enclave, set memcg to the current active mem_cgroup.
* This will be the root mem_cgroup if there is no active
* mem_cgroup.
*/
if (!memcg)
return get_mem_cgroup_from_mm(NULL);
return memcg;
}
/**
* sgx_encl_alloc_backing() - allocate a new backing storage page
* @encl: an enclave pointer
* @page_index: enclave page index
* @backing: data for accessing backing storage for the page
*
* When called from ksgxd, sets the active memcg from one of the
* mms in the enclave's mm_list prior to any backing page allocation,
* in order to ensure that shmem page allocations are charged to the
* enclave.
*
* Return:
* 0 on success,
* -errno otherwise.
*/
int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long page_index,
struct sgx_backing *backing)
{
struct mem_cgroup *encl_memcg = sgx_encl_get_mem_cgroup(encl);
struct mem_cgroup *memcg = set_active_memcg(encl_memcg);
int ret;
ret = sgx_encl_get_backing(encl, page_index, backing);
set_active_memcg(memcg);
mem_cgroup_put(encl_memcg);
return ret;
}
/**
* sgx_encl_lookup_backing() - retrieve an existing backing storage page
* @encl: an enclave pointer
* @page_index: enclave page index
* @backing: data for accessing backing storage for the page
*
* Retrieve a backing page for loading data back into an EPC page with ELDU.
* It is the caller's responsibility to ensure that it is appropriate to use
* sgx_encl_lookup_backing() rather than sgx_encl_alloc_backing(). If lookup is
* not used correctly, this will cause an allocation which is not accounted for.
*
* Return:
* 0 on success,
* -errno otherwise.
*/
int sgx_encl_lookup_backing(struct sgx_encl *encl, unsigned long page_index,
struct sgx_backing *backing)
{
return sgx_encl_get_backing(encl, page_index, backing);
}
/**
* sgx_encl_put_backing() - Unpin the backing storage
* @backing: data for accessing backing storage for the page

7
arch/x86/kernel/cpu/sgx/encl.h
View File

@ -103,10 +103,13 @@ static inline int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
unsigned long end, unsigned long vm_flags);
bool current_is_ksgxd(void);
void sgx_encl_release(struct kref *ref);
int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm);
int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long page_index,
struct sgx_backing *backing);
int sgx_encl_lookup_backing(struct sgx_encl *encl, unsigned long page_index,
struct sgx_backing *backing);
int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long page_index,
struct sgx_backing *backing);
void sgx_encl_put_backing(struct sgx_backing *backing);
int sgx_encl_test_and_clear_young(struct mm_struct *mm,
struct sgx_encl_page *page);

9
arch/x86/kernel/cpu/sgx/main.c
View File

@ -313,7 +313,7 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
sgx_encl_put_backing(backing);
if (!encl->secs_child_cnt && test_bit(SGX_ENCL_INITIALIZED, &encl->flags)) {
ret = sgx_encl_get_backing(encl, PFN_DOWN(encl->size),
ret = sgx_encl_alloc_backing(encl, PFN_DOWN(encl->size),
&secs_backing);
if (ret)
goto out;
@ -384,7 +384,7 @@ static void sgx_reclaim_pages(void)
page_index = PFN_DOWN(encl_page->desc - encl_page->encl->base);
mutex_lock(&encl_page->encl->lock);
ret = sgx_encl_get_backing(encl_page->encl, page_index, &backing[i]);
ret = sgx_encl_alloc_backing(encl_page->encl, page_index, &backing[i]);
if (ret) {
mutex_unlock(&encl_page->encl->lock);
goto skip;
@ -475,6 +475,11 @@ static bool __init sgx_page_reclaimer_init(void)
return true;
}
bool current_is_ksgxd(void)
{
return current == ksgxd_tsk;
}
static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
{
struct sgx_numa_node *node = &sgx_numa_nodes[nid];