arm64: Enable memory encrypt for Realms

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.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Co-developed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20241017131434.40935-10-steven.price@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: Suzuki K Poulose

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

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 */

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.
  */

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 */

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>
 
 static 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;
@@ -119,6 +132,9 @@ 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);

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)
 {