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Commit cab15ce6 authored by Catalin Marinas's avatar Catalin Marinas Committed by Will Deacon
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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. However, the kernel running on a CPU
implementation without User Access Override (ARMv8.2 onwards) 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 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_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_ng() macro. VM_READ is also checked now for page faults.

Reviewed-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 7419333f

arch/arm64/include/asm/pgtable-prot.h

+3 −2
Original line number Diff line number Diff line
@@ -70,12 +70,13 @@ 
#define PAGE_COPY_EXEC		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)

#define PAGE_READONLY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)

#define PAGE_READONLY_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)

#define PAGE_EXECONLY		__pgprot(_PAGE_DEFAULT | PTE_NG | PTE_PXN)



#define __P000  PAGE_NONE

#define __P001  PAGE_READONLY

#define __P010  PAGE_COPY

#define __P011  PAGE_COPY

#define __P100  PAGE_READONLY_EXEC

#define __P100  PAGE_EXECONLY

#define __P101  PAGE_READONLY_EXEC

#define __P110  PAGE_COPY_EXEC

#define __P111  PAGE_COPY_EXEC
@@ -84,7 +85,7 @@ 
#define __S001  PAGE_READONLY

#define __S010  PAGE_SHARED

#define __S011  PAGE_SHARED

#define __S100  PAGE_READONLY_EXEC

#define __S100  PAGE_EXECONLY

#define __S101  PAGE_READONLY_EXEC

#define __S110  PAGE_SHARED_EXEC

#define __S111  PAGE_SHARED_EXEC

arch/arm64/include/asm/pgtable.h

+5 −5
Original line number Diff line number Diff line
@@ -73,7 +73,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]; 
#define pte_write(pte)		(!!(pte_val(pte) & PTE_WRITE))

#define pte_exec(pte)		(!(pte_val(pte) & PTE_UXN))

#define pte_cont(pte)		(!!(pte_val(pte) & PTE_CONT))

#define pte_user(pte)		(!!(pte_val(pte) & PTE_USER))

#define pte_ng(pte)		(!!(pte_val(pte) & PTE_NG))



#ifdef CONFIG_ARM64_HW_AFDBM

#define pte_hw_dirty(pte)	(pte_write(pte) && !(pte_val(pte) & PTE_RDONLY))
@@ -84,8 +84,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]; 
#define pte_dirty(pte)		(pte_sw_dirty(pte) || pte_hw_dirty(pte))



#define pte_valid(pte)		(!!(pte_val(pte) & PTE_VALID))

#define pte_valid_not_user(pte) \

	((pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID)

#define pte_valid_global(pte) \

	((pte_val(pte) & (PTE_VALID | PTE_NG)) == PTE_VALID)

#define pte_valid_young(pte) \

	((pte_val(pte) & (PTE_VALID | PTE_AF)) == (PTE_VALID | PTE_AF))
@@ -168,7 +168,7 @@ static inline void set_pte(pte_t *ptep, pte_t pte) 
	 * Only if the new pte is valid and kernel, otherwise TLB maintenance

	 * or update_mmu_cache() have the necessary barriers.

	 */

	if (pte_valid_not_user(pte)) {

	if (pte_valid_global(pte)) {

		dsb(ishst);

		isb();

	}
@@ -202,7 +202,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, 
			pte_val(pte) &= ~PTE_RDONLY;

		else

			pte_val(pte) |= PTE_RDONLY;

		if (pte_user(pte) && pte_exec(pte) && !pte_special(pte))

		if (pte_ng(pte) && pte_exec(pte) && !pte_special(pte))

			__sync_icache_dcache(pte, addr);

	}

arch/arm64/mm/fault.c

+2 −3
Original line number Diff line number Diff line
@@ -251,8 +251,7 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr, 
good_area:

	/*

	 * Check that the permissions on the VMA allow for the fault which

	 * occurred. If we encountered a write or exec fault, we must have

	 * appropriate permissions, otherwise we allow any permission.

	 * occurred.

	 */

	if (!(vma->vm_flags & vm_flags)) {

		fault = VM_FAULT_BADACCESS;
@@ -288,7 +287,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
	struct task_struct *tsk;

	struct mm_struct *mm;

	int fault, sig, code;

	unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;

	unsigned long vm_flags = VM_READ | VM_WRITE;

	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;



	if (notify_page_fault(regs, esr))

mm/mmap.c

+5 −0
Original line number Diff line number Diff line
@@ -88,6 +88,11 @@ static void unmap_region(struct mm_struct *mm, 
 *		w: (no) no	w: (no) no	w: (copy) copy	w: (no) no

 *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes

 *

 * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and

 * MAP_PRIVATE:

 *								r: (no) no

 *								w: (no) no

 *								x: (yes) yes

 */

pgprot_t protection_map[16] = {

	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,