arm64: implement CONFIG_STRICT_MEMORY_RWX for arm64

In order to improve security, protect the sections
the kernel uses for the 1-to-1 mapping of memory
as strictly as possible (i.e. no writing on text,
executing data, etc.)

Change-Id: I6ef6837502b8af4f914512f95ff902276e191351
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>

arch/arm64/kernel/entry.S

@@ -139,7 +139,12 @@ tsk	.req	x28		// current thread_info
  * Interrupt handling.
  */
 	.macro	irq_handler
+#ifdef CONFIG_STRICT_MEMORY_RWX
+	ldr	x1, =handle_arch_irq
+	ldr	x1, [x1]
+#else
 	ldr	x1, handle_arch_irq
+#endif
 	mov	x0, sp
 	blr	x1
 	.endm
@@ -676,5 +681,9 @@ ENTRY(sys_rt_sigreturn_wrapper)
 	b	sys_rt_sigreturn
 ENDPROC(sys_rt_sigreturn_wrapper)
 
+#ifdef CONFIG_STRICT_MEMORY_RWX
+.data
+#endif
+
 ENTRY(handle_arch_irq)
 	.quad	0

arch/arm64/kernel/head.S

@@ -207,7 +207,11 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
 	msr	vttbr_el2, xzr
 
 	/* Hypervisor stub */
+#ifndef CONFIG_STRICT_MEMORY_RWX
 	adr	x0, __hyp_stub_vectors
+#else
+	ldr	x0, =__hyp_stub_vectors
+#endif
 	msr	vbar_el2, x0
 
 	/* spsr */

arch/arm64/kernel/vmlinux.lds.S

@@ -8,6 +8,9 @@
 #include <asm/thread_info.h>
 #include <asm/memory.h>
 #include <asm/page.h>
+#ifdef CONFIG_STRICT_MEMORY_RWX
+#include <asm/pgtable.h>
+#endif
 
 #define ARM_EXIT_KEEP(x)
 #define ARM_EXIT_DISCARD(x)	x
@@ -52,6 +55,9 @@ SECTIONS
 		_text = .;
 		HEAD_TEXT
 	}
+#ifdef CONFIG_STRICT_MEMORY_RWX
+	. = ALIGN(1<<SECTION_SHIFT);
+#endif
 	.text : {			/* Real text segment		*/
 		_stext = .;		/* Text and read-only data	*/
 			__exception_text_start = .;
@@ -68,19 +74,31 @@ SECTIONS
 		*(.got)			/* Global offset table		*/
 	}
 
+#ifdef CONFIG_STRICT_MEMORY_RWX
+	. = ALIGN(1<<SECTION_SHIFT);
+#endif
 	RO_DATA(PAGE_SIZE)
 	EXCEPTION_TABLE(8)
 	NOTES
 	_etext = .;			/* End of text and rodata section */
 
+#ifdef CONFIG_STRICT_MEMORY_RWX
+	. = ALIGN(1<<SECTION_SHIFT);
+#else
 	. = ALIGN(PAGE_SIZE);
+#endif
 	__init_begin = .;
 
 	INIT_TEXT_SECTION(8)
 	.exit.text : {
 		ARM_EXIT_KEEP(EXIT_TEXT)
 	}
+#ifdef CONFIG_STRICT_MEMORY_RWX
+	. = ALIGN(1<<SECTION_SHIFT);
+	__init_data_begin = .;
+#else
 	. = ALIGN(16);
+#endif
 	.init.data : {
 		INIT_DATA
 		INIT_SETUP(16)

arch/arm64/mm/init.c

@@ -343,11 +343,21 @@ void __init mem_init(void)
 	}
 }
 
+#ifdef CONFIG_STRICT_MEMORY_RWX
+void free_initmem(void)
+{
+	poison_init_mem(__init_data_begin, __init_end - __init_data_begin);
+	free_reserved_area(PAGE_ALIGN((unsigned long)&__init_data_begin),
+				  ((unsigned long)&__init_end) & PAGE_MASK,
+				  0, "unused kernel");
+}
+#else
 void free_initmem(void)
 {
 	poison_init_mem(__init_begin, __init_end - __init_begin);
 	free_initmem_default(0);
 }
+#endif
 
 #ifdef CONFIG_BLK_DEV_INITRD
 

arch/arm64/mm/mmu.c

@@ -185,6 +185,26 @@ static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
 	} while (pte++, addr += PAGE_SIZE, addr != end);
 }
 
+#ifdef CONFIG_STRICT_MEMORY_RWX
+pmdval_t get_pmd_prot_sect_kernel(unsigned long addr)
+{
+	if (addr >= (unsigned long)__init_data_begin)
+		return prot_sect_kernel | PMD_SECT_PXN;
+	if (addr >= (unsigned long)__init_begin)
+		return prot_sect_kernel | PMD_SECT_RDONLY;
+	if (addr >= (unsigned long)__start_rodata)
+		return prot_sect_kernel | PMD_SECT_RDONLY | PMD_SECT_PXN;
+	if (addr >= (unsigned long)_stext)
+		return prot_sect_kernel | PMD_SECT_RDONLY;
+	return prot_sect_kernel | PMD_SECT_PXN;
+}
+#else
+pmdval_t get_pmd_prot_sect_kernel(unsigned long addr)
+{
+	return prot_sect_kernel;
+}
+#endif
+
 static void __init alloc_init_pmd(pud_t *pud, unsigned long addr,
 				  unsigned long end, phys_addr_t phys)
 {
@@ -204,7 +224,8 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr,
 		next = pmd_addr_end(addr, end);
 		/* try section mapping first */
 		if (((addr | next | phys) & ~SECTION_MASK) == 0)
-			set_pmd(pmd, __pmd(phys | prot_sect_kernel));
+			set_pmd(pmd,
+				__pmd(phys | get_pmd_prot_sect_kernel(addr)));
 		else
 			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys));
 		phys += next - addr;

include/linux/mm.h

@@ -18,6 +18,10 @@
 #include <linux/bit_spinlock.h>
 #include <linux/shrinker.h>
 
+#ifdef CONFIG_STRICT_MEMORY_RWX
+extern char __init_data_begin[];
+#endif
+
 struct mempolicy;
 struct anon_vma;
 struct anon_vma_chain;