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arm64: Introduce execute-only page access permissions
The ARMv8 architecture allows execute-only user permissions by clearing the PTE_UXN and PTE_USER bits. The kernel, however, can still access such page, so execute-only page permission does not protect against read(2)/write(2) etc. accesses. Systems requiring such protection must implement/enable features like SECCOMP. This patch changes the arm64 __P100 and __S100 protection_map[] macros to the new __PAGE_EXECONLY attributes. A side effect is that pte_valid_user() no longer triggers for __PAGE_EXECONLY since PTE_USER isn't set. To work around this, the check is done on the PTE_NG bit via the pte_valid_ng() macro. VM_READ is also checked now for page faults. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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@ -90,6 +90,7 @@ extern pgprot_t pgprot_default;
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#define __PAGE_COPY_EXEC __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
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#define __PAGE_READONLY __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
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#define __PAGE_READONLY_EXEC __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
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#define __PAGE_EXECONLY __pgprot(_PAGE_DEFAULT | PTE_NG | PTE_PXN)
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#endif /* __ASSEMBLY__ */
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@ -97,7 +98,7 @@ extern pgprot_t pgprot_default;
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#define __P001 __PAGE_READONLY
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#define __P010 __PAGE_COPY
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#define __P011 __PAGE_COPY
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#define __P100 __PAGE_READONLY_EXEC
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#define __P100 __PAGE_EXECONLY
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#define __P101 __PAGE_READONLY_EXEC
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#define __P110 __PAGE_COPY_EXEC
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#define __P111 __PAGE_COPY_EXEC
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@ -106,7 +107,7 @@ extern pgprot_t pgprot_default;
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#define __S001 __PAGE_READONLY
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#define __S010 __PAGE_SHARED
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#define __S011 __PAGE_SHARED
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#define __S100 __PAGE_READONLY_EXEC
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#define __S100 __PAGE_EXECONLY
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#define __S101 __PAGE_READONLY_EXEC
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#define __S110 __PAGE_SHARED_EXEC
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#define __S111 __PAGE_SHARED_EXEC
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@ -143,8 +144,8 @@ extern struct page *empty_zero_page;
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#define pte_write(pte) (!!(pte_val(pte) & PTE_WRITE))
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#define pte_exec(pte) (!(pte_val(pte) & PTE_UXN))
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#define pte_valid_user(pte) \
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((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER))
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#define pte_valid_ng(pte) \
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((pte_val(pte) & (PTE_VALID | PTE_NG)) == (PTE_VALID | PTE_NG))
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static inline pte_t pte_wrprotect(pte_t pte)
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{
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@ -198,7 +199,7 @@ extern void __sync_icache_dcache(pte_t pteval, unsigned long addr);
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static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep, pte_t pte)
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{
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if (pte_valid_user(pte)) {
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if (pte_valid_ng(pte)) {
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if (!pte_special(pte) && pte_exec(pte))
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__sync_icache_dcache(pte, addr);
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if (pte_dirty(pte) && pte_write(pte))
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@ -173,8 +173,7 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
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good_area:
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/*
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* Check that the permissions on the VMA allow for the fault which
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* occurred. If we encountered a write or exec fault, we must have
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* appropriate permissions, otherwise we allow any permission.
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* occurred.
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*/
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if (!(vma->vm_flags & vm_flags)) {
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fault = VM_FAULT_BADACCESS;
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@ -196,7 +195,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
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struct task_struct *tsk;
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struct mm_struct *mm;
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int fault, sig, code;
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unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;
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unsigned long vm_flags = VM_READ | VM_WRITE;
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unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
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tsk = current;
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