[PATCH 6.18 046/314] arm64: io: Extract user memory type in ioremap_prot()

Sasha Levin
2026-03-10T11:25:22Z

From: Will Deacon <will@kernel.org>

[ Upstream commit 8f098037139b294050053123ab2bc0f819d08932 ]

The only caller of ioremap_prot() outside of the generic ioremap()
implementation is generic_access_phys(), which passes a 'pgprot_t' value
determined from the user mapping of the target 'pfn' being accessed by
the kernel. On arm64, the 'pgprot_t' contains all of the non-address
bits from the pte, including the permission controls, and so we end up
returning a new user mapping from ioremap_prot() which faults when
accessed from the kernel on systems with PAN:

| Unable to handle kernel read from unreadable memory at virtual address ffff80008ea89000
| ...
| Call trace:
| __memcpy_fromio+0x80/0xf8
| generic_access_phys+0x20c/0x2b8
| __access_remote_vm+0x46c/0x5b8
| access_remote_vm+0x18/0x30
| environ_read+0x238/0x3e8
| vfs_read+0xe4/0x2b0
| ksys_read+0xcc/0x178
| __arm64_sys_read+0x4c/0x68

Extract only the memory type from the user 'pgprot_t' in ioremap_prot()
and assert that we're being passed a user mapping, to protect us against
any changes in future that may require additional handling. To avoid
falsely flagging users of ioremap(), provide our own ioremap() macro
which simply wraps __ioremap_prot().

Cc: Zeng Heng <zengheng4@huawei.com>
Cc: Jinjiang Tu <tujinjiang@huawei.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Fixes: 893dea9ccd08 ("arm64: Add HAVE_IOREMAP_PROT support")
Reported-by: Jinjiang Tu <tujinjiang@huawei.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/io.h | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index cd2fddfe814ac..8cbd1e96fd50b 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -266,10 +266,23 @@ typedef int (*ioremap_prot_hook_t)(phys_addr_t phys_addr, size_t size,
int arm64_ioremap_prot_hook_register(const ioremap_prot_hook_t hook);
void __iomem *__ioremap_prot(phys_addr_t phys, size_t size, pgprot_t prot);

-#define ioremap_prot __ioremap_prot
+static inline void __iomem *ioremap_prot(phys_addr_t phys, size_t size,
+ pgprot_t user_prot)
+{
+ pgprot_t prot;
+ ptdesc_t user_prot_val = pgprot_val(user_prot);
+
+ if (WARN_ON_ONCE(!(user_prot_val & PTE_USER)))
+ return NULL;

-#define _PAGE_IOREMAP PROT_DEVICE_nGnRE
+ prot = __pgprot_modify(PAGE_KERNEL, PTE_ATTRINDX_MASK,
+ user_prot_val & PTE_ATTRINDX_MASK);
+ return __ioremap_prot(phys, size, prot);
+}
+#define ioremap_prot ioremap_prot

+#define ioremap(addr, size) \
+ __ioremap_prot((addr), (size), __pgprot(PROT_DEVICE_nGnRE))
#define ioremap_wc(addr, size) \
__ioremap_prot((addr), (size), __pgprot(PROT_NORMAL_NC))
#define ioremap_np(addr, size) \
--
2.51.0