[PATCH v6 09/11] arm64: Enable memory encrypt for Realms

From: Steven Price
Date: Fri Oct 04 2024 - 10:48:01 EST

From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

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.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Co-developed-by: Steven Price <steven.price@xxxxxxx>
Signed-off-by: Steven Price <steven.price@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
Changes since v5:
* Added comments and a WARN() in realm_set_memory_{en,de}crypted() to
explain that memory is leaked if the transition fails. This means the
callers no longer need to provide their own WARN.
Changed since v4:
* Reworked to use the new dispatcher for the mem_encrypt API
Changes since v3:
* Provide pgprot_{de,en}crypted() macros
* Rename __set_memory_encrypted() to __set_memory_enc_dec() since it
both encrypts and decrypts.
Changes since v2:
* Fix location of set_memory_{en,de}crypted() and export them.
* Break-before-make when changing the top bit of the IPA for
transitioning to/from shared.
---
arch/arm64/Kconfig | 3 +
arch/arm64/include/asm/mem_encrypt.h | 9 +++
arch/arm64/include/asm/pgtable.h | 5 ++
arch/arm64/include/asm/set_memory.h | 3 +
arch/arm64/kernel/rsi.c | 16 +++++
arch/arm64/mm/pageattr.c | 90 +++++++++++++++++++++++++++-
6 files changed, 123 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3e29b44d2d7b..ccea9c22d6df 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -21,6 +21,7 @@ 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
@@ -44,6 +45,8 @@ 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
index b0c9a86b13a4..f8f78f622dd2 100644
--- a/arch/arm64/include/asm/mem_encrypt.h
+++ b/arch/arm64/include/asm/mem_encrypt.h
@@ -2,6 +2,8 @@
#ifndef __ASM_MEM_ENCRYPT_H
#define __ASM_MEM_ENCRYPT_H

+#include <asm/rsi.h>
+
struct arm64_mem_crypt_ops {
int (*encrypt)(unsigned long addr, int numpages);
int (*decrypt)(unsigned long addr, int numpages);
@@ -12,4 +14,11 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops);
int set_memory_encrypted(unsigned long addr, int numpages);
int set_memory_decrypted(unsigned long addr, int numpages);

+int realm_register_memory_enc_ops(void);
+
+static inline bool force_dma_unencrypted(struct device *dev)
+{
+ return is_realm_world();
+}
+
#endif /* __ASM_MEM_ENCRYPT_H */
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index c329ea061dc9..7e4bdc8259a2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -684,6 +684,11 @@ static inline void set_pud_at(struct mm_struct *mm, unsigned long addr,
#define pgprot_nx(prot) \
__pgprot_modify(prot, PTE_MAYBE_GP, PTE_PXN)

+#define pgprot_decrypted(prot) \
+ __pgprot_modify(prot, PROT_NS_SHARED, PROT_NS_SHARED)
+#define pgprot_encrypted(prot) \
+ __pgprot_modify(prot, PROT_NS_SHARED, 0)
+
/*
* Mark the prot value as uncacheable and unbufferable.
*/
diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h
index 917761feeffd..37774c793006 100644
--- a/arch/arm64/include/asm/set_memory.h
+++ b/arch/arm64/include/asm/set_memory.h
@@ -15,4 +15,7 @@ int set_direct_map_invalid_noflush(struct page *page);
int set_direct_map_default_noflush(struct page *page);
bool kernel_page_present(struct page *page);

+int set_memory_encrypted(unsigned long addr, int numpages);
+int set_memory_decrypted(unsigned long addr, int numpages);
+
#endif /* _ASM_ARM64_SET_MEMORY_H */
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 58408f5add49..6f39275b43a7 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -7,8 +7,10 @@
#include <linux/memblock.h>
#include <linux/psci.h>
#include <linux/swiotlb.h>
+#include <linux/cc_platform.h>

#include <asm/io.h>
+#include <asm/mem_encrypt.h>
#include <asm/rsi.h>

struct realm_config config;
@@ -19,6 +21,17 @@ EXPORT_SYMBOL(prot_ns_shared);
DEFINE_STATIC_KEY_FALSE_RO(rsi_present);
EXPORT_SYMBOL(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_lower, ver_higher;
@@ -118,6 +131,9 @@ void __init arm64_rsi_init(void)
if (arm64_ioremap_prot_hook_register(realm_ioremap_hook))
return;

+ if (realm_register_memory_enc_ops())
+ return;
+
arm64_rsi_setup_memory();

static_branch_enable(&rsi_present);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 547a9e0b46c2..6ae6ae806454 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>
#include <asm/kfence.h>
@@ -23,14 +25,16 @@ bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED
bool can_set_direct_map(void)
{
/*
- * rodata_full and DEBUG_PAGEALLOC require linear map to be
- * mapped at page granularity, so that it is possible to
+ * rodata_full, DEBUG_PAGEALLOC and a Realm guest all require linear
+ * map to be mapped at page granularity, so that it is possible to
* protect/unprotect single pages.
*
* KFENCE pool requires page-granular mapping if initialized late.
+ *
+ * Realms need to make pages shared/protected at page granularity.
*/
return rodata_full || debug_pagealloc_enabled() ||
- arm64_kfence_can_set_direct_map();
+ arm64_kfence_can_set_direct_map() || is_realm_world();
}

static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
@@ -198,6 +202,86 @@ int set_direct_map_default_noflush(struct page *page)
PAGE_SIZE, change_page_range, &data);
}

+static int __set_memory_enc_dec(unsigned long addr,
+ int numpages,
+ bool encrypt)
+{
+ unsigned long set_prot = 0, clear_prot = 0;
+ phys_addr_t start, end;
+ int ret;
+
+ if (!is_realm_world())
+ return 0;
+
+ if (!__is_lm_address(addr))
+ return -EINVAL;
+
+ start = __virt_to_phys(addr);
+ end = start + numpages * PAGE_SIZE;
+
+ if (encrypt)
+ clear_prot = PROT_NS_SHARED;
+ else
+ set_prot = PROT_NS_SHARED;
+
+ /*
+ * Break the mapping before we make any changes to avoid stale TLB
+ * entries or Synchronous External Aborts caused by RIPAS_EMPTY
+ */
+ ret = __change_memory_common(addr, PAGE_SIZE * numpages,
+ __pgprot(set_prot),
+ __pgprot(clear_prot | PTE_VALID));
+
+ if (ret)
+ return ret;
+
+ if (encrypt)
+ ret = rsi_set_memory_range_protected(start, end);
+ else
+ ret = rsi_set_memory_range_shared(start, end);
+
+ if (ret)
+ return ret;
+
+ return __change_memory_common(addr, PAGE_SIZE * numpages,
+ __pgprot(PTE_VALID),
+ __pgprot(0));
+}
+
+static int realm_set_memory_encrypted(unsigned long addr, int numpages)
+{
+ int ret = __set_memory_enc_dec(addr, numpages, true);
+
+ /*
+ * If the request to change state fails, then the only sensible cause
+ * of action for the caller is to leak the memory
+ */
+ WARN(ret, "Failed to encrypt memory, %d pages will be leaked",
+ numpages);
+
+ return ret;
+}
+
+static int realm_set_memory_decrypted(unsigned long addr, int numpages)
+{
+ int ret = __set_memory_enc_dec(addr, numpages, false);
+
+ WARN(ret, "Failed to decrypt memory, %d pages will be leaked",
+ numpages);
+
+ return ret;
+}
+
+static const struct arm64_mem_crypt_ops realm_crypt_ops = {
+ .encrypt = realm_set_memory_encrypted,
+ .decrypt = realm_set_memory_decrypted,
+};
+
+int realm_register_memory_enc_ops(void)
+{
+ return arm64_mem_crypt_ops_register(&realm_crypt_ops);
+}
+
#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
--
2.34.1