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Subject[RFC v2 04/26] mm/asi: Functions to track buffers allocated for an ASI page-table
Date
Add functions to track buffers allocated for an ASI page-table. An ASI
page-table can have direct references to the kernel page table, at
different levels (PGD, P4D, PUD, PMD). When freeing an ASI page-table,
we should make sure that we free parts actually allocated for the ASI
page-table, and not parts of the kernel page table referenced from the
ASI page-table. To do so, we will keep track of buffers when building
the ASI page-table.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
arch/x86/include/asm/asi.h | 26 +++++++++++
arch/x86/mm/Makefile | 2 +-
arch/x86/mm/asi.c | 3 +
arch/x86/mm/asi_pagetable.c | 99 +++++++++++++++++++++++++++++++++++++++++++
4 files changed, 129 insertions(+), 1 deletions(-)
create mode 100644 arch/x86/mm/asi_pagetable.c

diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
index 013d77a..3d965e6 100644
--- a/arch/x86/include/asm/asi.h
+++ b/arch/x86/include/asm/asi.h
@@ -8,12 +8,35 @@

#include <linux/spinlock.h>
#include <asm/pgtable.h>
+#include <linux/xarray.h>
+
+enum page_table_level {
+ PGT_LEVEL_PTE,
+ PGT_LEVEL_PMD,
+ PGT_LEVEL_PUD,
+ PGT_LEVEL_P4D,
+ PGT_LEVEL_PGD
+};

#define ASI_FAULT_LOG_SIZE 128

struct asi {
spinlock_t lock; /* protect all attributes */
pgd_t *pgd; /* ASI page-table */
+
+ /*
+ * An ASI page-table can have direct references to the full kernel
+ * page-table, at different levels (PGD, P4D, PUD, PMD). When freeing
+ * an ASI page-table, we should make sure that we free parts actually
+ * allocated for the ASI page-table, and not part of the full kernel
+ * page-table referenced from the ASI page-table.
+ *
+ * To do so, the backend_pages XArray is used to keep track of pages
+ * used for the kernel isolation page-table.
+ */
+ struct xarray backend_pages; /* page-table pages */
+ unsigned long backend_pages_count; /* pages count */
+
spinlock_t fault_lock; /* protect fault_log */
unsigned long fault_log[ASI_FAULT_LOG_SIZE];
bool fault_stack; /* display stack of fault? */
@@ -43,6 +66,9 @@ struct asi_session {

DECLARE_PER_CPU_PAGE_ALIGNED(struct asi_session, cpu_asi_session);

+void asi_init_backend(struct asi *asi);
+void asi_fini_backend(struct asi *asi);
+
extern struct asi *asi_create(void);
extern void asi_destroy(struct asi *asi);
extern int asi_enter(struct asi *asi);
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index dae5c8a..b972f0f 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -49,7 +49,7 @@ obj-$(CONFIG_X86_INTEL_MPX) += mpx.o
obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o
obj-$(CONFIG_RANDOMIZE_MEMORY) += kaslr.o
obj-$(CONFIG_PAGE_TABLE_ISOLATION) += pti.o
-obj-$(CONFIG_ADDRESS_SPACE_ISOLATION) += asi.o
+obj-$(CONFIG_ADDRESS_SPACE_ISOLATION) += asi.o asi_pagetable.o

obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_identity.o
diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
index 717160d..dfde245 100644
--- a/arch/x86/mm/asi.c
+++ b/arch/x86/mm/asi.c
@@ -111,6 +111,7 @@ struct asi *asi_create(void)
asi->pgd = page_address(page);
spin_lock_init(&asi->lock);
spin_lock_init(&asi->fault_lock);
+ asi_init_backend(asi);

err = asi_init_mapping(asi);
if (err)
@@ -132,6 +133,8 @@ void asi_destroy(struct asi *asi)
if (asi->pgd)
free_page((unsigned long)asi->pgd);

+ asi_fini_backend(asi);
+
kfree(asi);
}
EXPORT_SYMBOL(asi_destroy);
diff --git a/arch/x86/mm/asi_pagetable.c b/arch/x86/mm/asi_pagetable.c
new file mode 100644
index 0000000..7a8f791
--- /dev/null
+++ b/arch/x86/mm/asi_pagetable.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ *
+ */
+
+#include <asm/asi.h>
+
+/*
+ * Get the pointer to the beginning of a page table directory from a page
+ * table directory entry.
+ */
+#define ASI_BACKEND_PAGE_ALIGN(entry) \
+ ((typeof(entry))(((unsigned long)(entry)) & PAGE_MASK))
+
+/*
+ * Pages used to build the address space isolation page-table are stored
+ * in the backend_pages XArray. Each entry in the array is a logical OR
+ * of the page address and the page table level (PTE, PMD, PUD, P4D) this
+ * page is used for in the address space isolation page-table.
+ *
+ * As a page address is aligned with PAGE_SIZE, we have plenty of space
+ * for storing the page table level (which is a value between 0 and 4) in
+ * the low bits of the page address.
+ *
+ */
+
+#define ASI_BACKEND_PAGE_ENTRY(addr, level) \
+ ((typeof(addr))(((unsigned long)(addr)) | ((unsigned long)(level))))
+#define ASI_BACKEND_PAGE_ADDR(entry) \
+ ((void *)(((unsigned long)(entry)) & PAGE_MASK))
+#define ASI_BACKEND_PAGE_LEVEL(entry) \
+ ((enum page_table_level)(((unsigned long)(entry)) & ~PAGE_MASK))
+
+static int asi_add_backend_page(struct asi *asi, void *addr,
+ enum page_table_level level)
+{
+ unsigned long index;
+ void *old_entry;
+
+ if ((!addr) || ((unsigned long)addr) & ~PAGE_MASK)
+ return -EINVAL;
+
+ lockdep_assert_held(&asi->lock);
+ index = asi->backend_pages_count;
+
+ old_entry = xa_store(&asi->backend_pages, index,
+ ASI_BACKEND_PAGE_ENTRY(addr, level),
+ GFP_KERNEL);
+ if (xa_is_err(old_entry))
+ return xa_err(old_entry);
+ if (old_entry)
+ return -EBUSY;
+
+ asi->backend_pages_count++;
+
+ return 0;
+}
+
+void asi_init_backend(struct asi *asi)
+{
+ xa_init(&asi->backend_pages);
+}
+
+void asi_fini_backend(struct asi *asi)
+{
+ unsigned long index;
+ void *entry;
+
+ if (asi->backend_pages_count) {
+ xa_for_each(&asi->backend_pages, index, entry)
+ free_page((unsigned long)ASI_BACKEND_PAGE_ADDR(entry));
+ }
+}
+
+/*
+ * Check if an offset in the address space isolation page-table is valid,
+ * i.e. check that the offset is on a page effectively belonging to the
+ * address space isolation page-table.
+ */
+static bool asi_valid_offset(struct asi *asi, void *offset)
+{
+ unsigned long index;
+ void *addr, *entry;
+ bool valid;
+
+ addr = ASI_BACKEND_PAGE_ALIGN(offset);
+ valid = false;
+
+ lockdep_assert_held(&asi->lock);
+ xa_for_each(&asi->backend_pages, index, entry) {
+ if (ASI_BACKEND_PAGE_ADDR(entry) == addr) {
+ valid = true;
+ break;
+ }
+ }
+
+ return valid;
+}
--
1.7.1
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