[RFC PATCH 10/14] arm64: Enable memory encrypt for Realms

Steven Price
2023-01-27T11:30:48Z

Use the memory encryption APIs to trigger a RSI call to request a
transition between protected memory and shared memory (or vice versa)
and updating the kernel's linear map of modified pages to flip the top
bit of the IPA. This requires that block mappings are not used in the
direct map for realm guests.

Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
arch/arm64/Kconfig | 3 ++
arch/arm64/include/asm/mem_encrypt.h | 19 +++++++++++
arch/arm64/kernel/rsi.c | 12 +++++++
arch/arm64/mm/pageattr.c | 48 +++++++++++++++++++++++++---
4 files changed, 78 insertions(+), 4 deletions(-)
create mode 100644 arch/arm64/include/asm/mem_encrypt.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 03934808b2ed..0aac44a993ac 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -20,6 +20,7 @@ config ARM64
select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
select ARCH_HAS_CACHE_LINE_SIZE
+ select ARCH_HAS_CC_PLATFORM
select ARCH_HAS_CURRENT_STACK_POINTER
select ARCH_HAS_DEBUG_VIRTUAL
select ARCH_HAS_DEBUG_VM_PGTABLE
@@ -39,6 +40,8 @@ config ARM64
select ARCH_HAS_SETUP_DMA_OPS
select ARCH_HAS_SET_DIRECT_MAP
select ARCH_HAS_SET_MEMORY
+ select ARCH_HAS_MEM_ENCRYPT
+ select ARCH_HAS_FORCE_DMA_UNENCRYPTED
select ARCH_STACKWALK
select ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_HAS_STRICT_MODULE_RWX
diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h
new file mode 100644
index 000000000000..7381f9585321
--- /dev/null
+++ b/arch/arm64/include/asm/mem_encrypt.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2023 ARM Ltd.
+ */
+
+#ifndef __ASM_MEM_ENCRYPT_H
+#define __ASM_MEM_ENCRYPT_H
+
+#include <asm/rsi.h>
+
+/* All DMA must be to non-secure memory for now */
+static inline bool force_dma_unencrypted(struct device *dev)
+{
+ return is_realm_world();
+}
+
+int set_memory_encrypted(unsigned long addr, int numpages);
+int set_memory_decrypted(unsigned long addr, int numpages);
+#endif
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 1a07eefdd2e9..1cc292826f2b 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -6,6 +6,7 @@
#include <linux/jump_label.h>
#include <linux/memblock.h>
#include <linux/swiotlb.h>
+#include <linux/cc_platform.h>

#include <asm/rsi.h>

@@ -18,6 +19,17 @@ unsigned int phys_mask_shift = CONFIG_ARM64_PA_BITS;

DEFINE_STATIC_KEY_FALSE_RO(rsi_present);

+bool cc_platform_has(enum cc_attr attr)
+{
+ switch (attr) {
+ case CC_ATTR_MEM_ENCRYPT:
+ return is_realm_world();
+ default:
+ return false;
+ }
+}
+EXPORT_SYMBOL_GPL(cc_platform_has);
+
static bool rsi_version_matches(void)
{
unsigned long ver = rsi_get_version();
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 79dd201c59d8..bbd7364dd9a8 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -5,10 +5,12 @@
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
+#include <linux/mem_encrypt.h>
#include <linux/sched.h>
#include <linux/vmalloc.h>

#include <asm/cacheflush.h>
+#include <asm/pgtable-prot.h>
#include <asm/set_memory.h>
#include <asm/tlbflush.h>

@@ -22,12 +24,12 @@ bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED
bool can_set_direct_map(void)
{
/*
- * rodata_full, DEBUG_PAGEALLOC and KFENCE require linear map to be
- * mapped at page granularity, so that it is possible to
- * protect/unprotect single pages.
+ * rodata_full, DEBUG_PAGEALLOC, KFENCE and a Realm guest all require
+ * linear map to be mapped at page granularity, so that it is possible
+ * to protect/unprotect single pages.
*/
return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
- IS_ENABLED(CONFIG_KFENCE);
+ IS_ENABLED(CONFIG_KFENCE) || is_realm_world();
}

static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
@@ -38,6 +40,7 @@ static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
pte = clear_pte_bit(pte, cdata->clear_mask);
pte = set_pte_bit(pte, cdata->set_mask);

+ /* TODO: Break before make for PROT_NS_SHARED updates */
set_pte(ptep, pte);
return 0;
}
@@ -190,6 +193,43 @@ int set_direct_map_default_noflush(struct page *page)
PAGE_SIZE, change_page_range, &data);
}

+static int __set_memory_encrypted(unsigned long addr,
+ int numpages,
+ bool encrypt)
+{
+ unsigned long set_prot = 0, clear_prot = 0;
+ phys_addr_t start, end;
+
+ if (!is_realm_world())
+ return 0;
+
+ WARN_ON(!__is_lm_address(addr));
+ start = __virt_to_phys(addr);
+ end = start + numpages * PAGE_SIZE;
+
+ if (encrypt) {
+ clear_prot = PROT_NS_SHARED;
+ set_memory_range_protected(start, end);
+ } else {
+ set_prot = PROT_NS_SHARED;
+ set_memory_range_shared(start, end);
+ }
+
+ return __change_memory_common(addr, PAGE_SIZE * numpages,
+ __pgprot(set_prot),
+ __pgprot(clear_prot));
+}
+
+int set_memory_encrypted(unsigned long addr, int numpages)
+{
+ return __set_memory_encrypted(addr, numpages, true);
+}
+
+int set_memory_decrypted(unsigned long addr, int numpages)
+{
+ return __set_memory_encrypted(addr, numpages, false);
+}
+
#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
--
2.34.1