CVE-2014-9803: Data Processing Errors (CWE-19)
value: arch/arm64/include/asm/pgtable.h in the Linux kernel before 3.15-rc5-next-20140519, as used in Android before 2016-07-05 on Nexus 5X and 6P devices, mishandles execute-only pages, which allows attackers to gain privileges via a crafted application, aka Android internal bug 28557020.
CWE description: Weaknesses in this category are typically found in functionality that processes data. Data processing is the manipulation of input to retrieve or save information.
CVSS v3 base score: 7.8
Published: 2016-07-11T01:59Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: arch/arm64/include/asm/pgtable.h, arch/arm64/mm/fault.c
Commit date: 2014-05-16 16:44:32 +0100
Commit message: Revert "arm64: Introduce execute-only page access permissions"

This reverts commit bc07c2c6e9ed125d362af0214b6313dca180cb08.

While the aim is increased security for --x memory maps, it does not
protect against kernel level reads. Until SECCOMP is implemented for
arm64, revert this patch to avoid giving a false idea of execute-only
mappings.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Diff: diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index e4c60d6e18b8c6..aa150ed99f222e 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -84,26 +84,25 @@ extern void __pgd_error(const char *file, int line, unsigned long val);
 #define PAGE_SHARED_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
 #define PAGE_COPY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
 #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_EXECONLY
+#define __P100  PAGE_READONLY_EXEC
 #define __P101  PAGE_READONLY_EXEC
 #define __P110  PAGE_COPY_EXEC
 #define __P111  PAGE_COPY_EXEC
 
 #define __S000  PAGE_NONE
 #define __S001  PAGE_READONLY
 #define __S010  PAGE_SHARED
 #define __S011  PAGE_SHARED
-#define __S100  PAGE_EXECONLY
+#define __S100  PAGE_READONLY_EXEC
 #define __S101  PAGE_READONLY_EXEC
 #define __S110  PAGE_SHARED_EXEC
 #define __S111  PAGE_SHARED_EXEC
 
 /*
@@ -135,12 +134,12 @@ extern struct page *empty_zero_page;
 #define pte_young(pte)		(!!(pte_val(pte) & PTE_AF))
 #define pte_special(pte)	(!!(pte_val(pte) & PTE_SPECIAL))
 #define pte_write(pte)		(!!(pte_val(pte) & PTE_WRITE))
 #define pte_exec(pte)		(!(pte_val(pte) & PTE_UXN))
 
-#define pte_valid_ng(pte) \
-	((pte_val(pte) & (PTE_VALID | PTE_NG)) == (PTE_VALID | PTE_NG))
+#define pte_valid_user(pte) \
+	((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER))
 
 static inline pte_t pte_wrprotect(pte_t pte)
 {
 	pte_val(pte) &= ~PTE_WRITE;
 	return pte;
@@ -190,11 +189,11 @@ static inline void set_pte(pte_t *ptep, pte_t pte)
 extern void __sync_icache_dcache(pte_t pteval, unsigned long addr);
 
 static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t pte)
 {
-	if (pte_valid_ng(pte)) {
+	if (pte_valid_user(pte)) {
 		if (!pte_special(pte) && pte_exec(pte))
 			__sync_icache_dcache(pte, addr);
 		if (pte_dirty(pte) && pte_write(pte))
 			pte_val(pte) &= ~PTE_RDONLY;
 		else
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 89c6763d5e7e67..bcc965e2cce1fe 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -171,11 +171,12 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
 	 * it.
 	 */
 good_area:
 	/*
 	 * Check that the permissions on the VMA allow for the fault which
-	 * occurred.
+	 * occurred. If we encountered a write or exec fault, we must have
+	 * appropriate permissions, otherwise we allow any permission.
 	 */
 	if (!(vma->vm_flags & vm_flags)) {
 		fault = VM_FAULT_BADACCESS;
 		goto out;
 	}
@@ -193,11 +194,11 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 				   struct pt_regs *regs)
 {
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	int fault, sig, code;
-	unsigned long vm_flags = VM_READ | VM_WRITE;
+	unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;
 	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
 	tsk = current;
 	mm  = tsk->mm;
 

Vulnerable code: #define PAGE_EXECONLY		__pgprot(_PAGE_DEFAULT | PTE_NG | PTE_PXN)
#define __P100  PAGE_EXECONLY
#define __S100  PAGE_EXECONLY
#define pte_valid_ng(pte) \
	((pte_val(pte) & (PTE_VALID | PTE_NG)) == (PTE_VALID | PTE_NG))
	if (pte_valid_ng(pte)) {
	 * occurred.
	unsigned long vm_flags = VM_READ | VM_WRITE;
Fixed code: #define __P100  PAGE_READONLY_EXEC
#define __S100  PAGE_READONLY_EXEC
#define pte_valid_user(pte) \
	((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER))
	if (pte_valid_user(pte)) {
	 * occurred. If we encountered a write or exec fault, we must have
	 * appropriate permissions, otherwise we allow any permission.
	unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;