[PATCH 2/2] arm64: Add encrypt/decrypt support for vmalloc regions
From: Shanker Donthineni
Date: Sun Aug 10 2025 - 20:25:11 EST
On ARM64 systems with CCA (Confidential Compute Architecture) enabled,
the kernel may need to change the encryption attributes of memory
regions. The existing implementation of set_memory_encrypted() and
set_memory_decrypted() assumes that the input address is part of the
linear mapping region '__is_lm_address()', and fails with -EINVAL
otherwise.
This breaks use cases where the memory region resides in the vmalloc
area, which is mapped in non-linear mapping region.
This patch introduces a new helper, realm_set_memory(), which detects
whether the given address is from a non-linear mapping. If so, it uses
vmalloc_to_page() to resolve each page’s physical address and applies
attribute changes one page at a time. For the linear address regions,
it maintains the existing fast-path.
This change ensures that encrypted/decrypted memory attribute updates
correctly for all memory regions, including those allocated via vmap(),
module allocations, or other vmalloc-backed paths.
Call stack of Realm crash, QEMU hypervisor + NVME device (emulated):
...
Freeing unused kernel memory: 6336K
Run /sbin/init as init process
Internal error: synchronous external abort: 0000000096000250 [#1] SMP
Modules linked in:
CPU: 0 UID: 0 PID: 64 Comm: lsblk Not tainted 6.15.5 #2 PREEMPT(undef)
Hardware name: linux,dummy-virt (DT)
pstate: 43400005 (nZcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __pi_memset_generic+0x16c/0x188
lr : dma_alloc_from_pool+0xd0/0x1b8
sp : ffff80008335b350
x29: ffff80008335b350 x28: ffff800083162000 x27: ffff80008335b3c0
x26: ffff80008144f000 x25: ffff8000801a27e8 x24: ffff800081e14000
x23: ffffc1ffc0000000 x22: 0000000000001000 x21: ffff800081458310
x20: 0000000042a40000 x19: ffff00000232fcc0 x18: 0000000000200000
x17: 00000000000120c0 x16: ffff0000795520c0 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : ffff800083162000 x7 : 0000000000000000 x6 : 000000000000003f
x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000004
x2 : 0000000000000fc0 x1 : 0000000000000000 x0 : ffff800083162000
Call trace:
__pi_memset_generic+0x16c/0x188 (P)
dma_direct_alloc_from_pool+0xc4/0x230
dma_direct_alloc+0x80/0x4a0
dma_alloc_attrs+0x94/0x238
dma_pool_alloc+0x128/0x258
nvme_prep_rq.part.0+0x5f0/0x950
nvme_queue_rq+0x78/0x1e8
blk_mq_dispatch_rq_list+0x10c/0x6f0
__blk_mq_sched_dispatch_requests+0x4a0/0x580
blk_mq_sched_dispatch_requests+0x38/0xa0
blk_mq_run_hw_queue+0x288/0x2f8
blk_mq_flush_plug_list+0x134/0x630
__blk_flush_plug+0x100/0x168
blk_finish_plug+0x40/0x60
read_pages+0x1a0/0x2b0
page_cache_ra_unbounded+0x1f8/0x268
force_page_cache_ra+0xa4/0xe0
page_cache_sync_ra+0x48/0x268
filemap_get_pages+0xf4/0x7a0
filemap_read+0xf0/0x448
blkdev_read_iter+0x8c/0x1a8
vfs_read+0x288/0x330
ksys_read+0x78/0x118
__arm64_sys_read+0x24/0x40
invoke_syscall+0x50/0x120
el0_svc_common.constprop.0+0x48/0xf0
do_el0_svc+0x24/0x38
el0_svc+0x34/0xf8
el0t_64_sync_handler+0x10c/0x138
el0t_64_sync+0x1ac/0x1b0
Signed-off-by: Shanker Donthineni <sdonthineni@xxxxxxxxxx>
---
arch/arm64/mm/pageattr.c | 55 +++++++++++++++++++++++++++++++++++-----
1 file changed, 48 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 04d4a8f676db4..65c3322a86b49 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -202,21 +202,26 @@ int set_direct_map_default_noflush(struct page *page)
PAGE_SIZE, change_page_range, &data);
}
+/*
+ * Common function for setting memory encryption or decryption attributes.
+ *
+ * @addr: Virtual start address of the memory region
+ * @start: Corresponding physical start address
+ * @numpages: Number of pages to update
+ * @encrypt: If true, set memory as encrypted; if false, decrypt
+ */
static int __set_memory_enc_dec(unsigned long addr,
+ phys_addr_t start,
int numpages,
bool encrypt)
{
unsigned long set_prot = 0, clear_prot = 0;
- phys_addr_t start, end;
+ phys_addr_t 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)
@@ -248,9 +253,45 @@ static int __set_memory_enc_dec(unsigned long addr,
__pgprot(0));
}
+/*
+ * Wrapper for __set_memory_enc_dec() that handles both linear-mapped
+ * and vmalloc/module memory regions.
+ *
+ * If the address is in the linear map, we can directly compute the
+ * physical address. If not (e.g. vmalloc memory), we walk each page
+ * and call the attribute update individually.
+ */
+static int realm_set_memory(unsigned long addr, int numpages, bool encrypt)
+{
+ phys_addr_t start;
+ struct page *page;
+ int ret, i;
+
+ if (__is_lm_address(addr)) {
+ start = __virt_to_phys(addr);
+ return __set_memory_enc_dec(addr, start, numpages, encrypt);
+ }
+
+ for (i = 0; i < numpages; i++) {
+ page = vmalloc_to_page((void *)addr);
+ if (!page)
+ return -EINVAL;
+
+ start = page_to_phys(page);
+ ret = __set_memory_enc_dec(addr, start, 1, encrypt);
+ if (ret)
+ return ret;
+
+ addr += PAGE_SIZE;
+ }
+
+ return 0;
+}
+
static int realm_set_memory_encrypted(unsigned long addr, int numpages)
{
- int ret = __set_memory_enc_dec(addr, numpages, true);
+ int ret = realm_set_memory(addr, numpages, true);
+
/*
* If the request to change state fails, then the only sensible cause
@@ -264,7 +305,7 @@ static int realm_set_memory_encrypted(unsigned long addr, int numpages)
static int realm_set_memory_decrypted(unsigned long addr, int numpages)
{
- int ret = __set_memory_enc_dec(addr, numpages, false);
+ int ret = realm_set_memory(addr, numpages, false);
WARN(ret, "Failed to decrypt memory, %d pages will be leaked",
numpages);
--
2.25.1