[RFC PATCH v2 3/5] dma-mapping: Decrypt memory on remap

Mostafa Saleh
2026-03-30T14:51:40Z

In case memory needs to be remapped on systems with
force_dma_unencrypted(), where this memory is not allocated
from a restricted-dma pool, this was currently ignored, while only
setting the decrypted pgprot in the remapped alias.

The memory still needs to be decrypted in that case.

With memory decryption, don't allow highmem allocations, but that
shouldn't be a problem on such modern systems.

Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Fixes: f3c962226dbe ("dma-direct: clean up the remapping checks in dma_direct_alloc")
Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
kernel/dma/direct.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 1a402bb956d9..a4260689bcc8 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -203,6 +203,7 @@ static void *dma_direct_alloc_no_mapping(struct device *dev, size_t size,
void *dma_direct_alloc(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
{
+ bool allow_highmem = !force_dma_unencrypted(dev);
bool remap = false, set_uncached = false;
struct page *page;
void *ret;
@@ -251,7 +252,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);

/* we always manually zero the memory once we are done */
- page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
+ page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, allow_highmem);
if (!page)
return NULL;

@@ -265,6 +266,9 @@ void *dma_direct_alloc(struct device *dev, size_t size,
set_uncached = false;
}

+ if (dma_set_decrypted(dev, page_address(page), size))
+ goto out_leak_pages;
+
if (remap) {
pgprot_t prot = dma_pgprot(dev, PAGE_KERNEL, attrs);

@@ -278,11 +282,9 @@ void *dma_direct_alloc(struct device *dev, size_t size,
ret = dma_common_contiguous_remap(page, size, prot,
__builtin_return_address(0));
if (!ret)
- goto out_free_pages;
+ goto out_encrypt_pages;
} else {
ret = page_address(page);
- if (dma_set_decrypted(dev, ret, size))
- goto out_leak_pages;
}

memset(ret, 0, size);
@@ -300,7 +302,6 @@ void *dma_direct_alloc(struct device *dev, size_t size,
out_encrypt_pages:
if (dma_set_encrypted(dev, page_address(page), size))
return NULL;
-out_free_pages:
__dma_direct_free_pages(dev, page, size);
return NULL;
out_leak_pages:
@@ -339,7 +340,12 @@ void dma_direct_free(struct device *dev, size_t size,
return;

if (is_vmalloc_addr(cpu_addr)) {
+ void *vaddr = page_address(dma_direct_to_page(dev, dma_addr));
+
vunmap(cpu_addr);
+
+ if (dma_set_encrypted(dev, vaddr, size))
+ return;
} else {
if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
arch_dma_clear_uncached(cpu_addr, size);
--
2.53.0.1185.g05d4b7b318-goog