From bb756b11ad63832ebee58caf9e8f9381eaecff9f Mon Sep 17 00:00:00 2001 From: Zeng Heng Date: Fri, 11 Sep 2026 09:58:59 +0800 Subject: [PATCH] arm64: io: Reject non-user protection in ioremap_prot() Mapping a stack-top page via /dev/mem with PROT_NONE and then reading that process's /proc//cmdline triggers a spurious WARN in ioremap_prot() through generic_access_phys(): WARNING: ./arch/arm64/include/asm/io.h:275 at generic_access_phys Call trace: generic_access_phys+0x1c8/0x228 (P) __access_remote_vm+0x2b4/0x398 access_remote_vm+0x14/0x30 get_mm_cmdline+0xf8/0x2a0 proc_pid_cmdline_read+0x68/0x120 generic_access_phys() passes the protection derived from the user PTE to ioremap_prot(). On arm64, a PROT_NONE mapping is represented by a present-invalid PTE, so pte_present() still returns true and the protection reaches ioremap_prot(). A PROT_NONE mapping does not have PTE_USER, causing the existing WARN_ON_ONCE() in ioremap_prot() to fire even though this is a valid user mapping. Execute-only mappings have the same issue and must not be readable through this path either. ioremap_prot() should therefore reject protection values without PTE_USER without warning. This makes the access fail cleanly for PROT_NONE and execute-only mappings while retaining the existing user-protection contract. Fixes: 8f098037139b ("arm64: io: Extract user memory type in ioremap_prot()") Signed-off-by: Zeng Heng Reviewed-by: Catalin Marinas Signed-off-by: Will Deacon --- arch/arm64/include/asm/io.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h index 49a7002661a9..9aa0bb08ab60 100644 --- a/arch/arm64/include/asm/io.h +++ b/arch/arm64/include/asm/io.h @@ -280,7 +280,8 @@ static inline void __iomem *ioremap_prot(phys_addr_t phys, size_t size, pgprot_t prot; ptval_t user_prot_val = pgprot_val(user_prot); - if (WARN_ON_ONCE(!(user_prot_val & PTE_USER))) + /* Reject PROT_NONE and exec-only */ + if (!(user_prot_val & PTE_USER)) return NULL; prot = __pgprot_modify(PAGE_KERNEL, PTE_ATTRINDX_MASK,