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Commit 19accfd3 authored by Russell King's avatar Russell King
Browse files

ARM: move vector stubs 



Move the machine vector stubs into the page above the vector page,
which we can prevent from being visible to userspace.  Also move
the reset stub, and place the swi vector at a location that the
'ldr' can get to it.

This hides pointers into the kernel which could give valuable
information to attackers, and reduces the number of exploitable
instructions at a fixed address.

Cc: <stable@vger.kernel.org>
Acked-by: default avatarNicolas Pitre <nico@linaro.org>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 5b43e7a3

arch/arm/Kconfig

+2 −1
Original line number Diff line number Diff line
@@ -218,7 +218,8 @@ config VECTORS_BASE 
	default DRAM_BASE if REMAP_VECTORS_TO_RAM

	default 0x00000000

	help

	  The base address of exception vectors.

	  The base address of exception vectors.  This must be two pages

	  in size.



config ARM_PATCH_PHYS_VIRT

	bool "Patch physical to virtual translations at runtime" if EMBEDDED

arch/arm/kernel/entry-armv.S

+24 −26
Original line number Diff line number Diff line
@@ -944,9 +944,9 @@ __kuser_helper_end: 
/*

 * Vector stubs.

 *

 * This code is copied to 0xffff0200 so we can use branches in the

 * vectors, rather than ldr's.  Note that this code must not

 * exceed 0x300 bytes.

 * This code is copied to 0xffff1000 so we can use branches in the

 * vectors, rather than ldr's.  Note that this code must not exceed

 * a page size.

 *

 * Common stub entry macro:

 *   Enter in IRQ mode, spsr = SVC/USR CPSR, lr = SVC/USR PC
@@ -995,6 +995,15 @@ ENDPROC(vector_\name) 


	.globl	__stubs_start

__stubs_start:

	@ This must be the first word

	.word	vector_swi



vector_rst:

 ARM(	swi	SYS_ERROR0	)

 THUMB(	svc	#0		)

 THUMB(	nop			)

	b	vector_und



/*

 * Interrupt dispatcher

 */
@@ -1088,6 +1097,16 @@ __stubs_start: 


	.align	5



/*=============================================================================

 * Address exception handler

 *-----------------------------------------------------------------------------

 * These aren't too critical.

 * (they're not supposed to happen, and won't happen in 32-bit data mode).

 */



vector_addrexcptn:

	b	vector_addrexcptn



/*=============================================================================

 * Undefined FIQs

 *-----------------------------------------------------------------------------
@@ -1101,35 +1120,14 @@ __stubs_start: 
vector_fiq:

	subs	pc, lr, #4



/*=============================================================================

 * Address exception handler

 *-----------------------------------------------------------------------------

 * These aren't too critical.

 * (they're not supposed to happen, and won't happen in 32-bit data mode).

 */



vector_addrexcptn:

	b	vector_addrexcptn



/*

 * We group all the following data together to optimise

 * for CPUs with separate I & D caches.

 */

	.align	5



.LCvswi:

	.word	vector_swi



	.globl	__stubs_end

__stubs_end:



	.equ	stubs_offset, __vectors_start + 0x200 - __stubs_start

	.equ	stubs_offset, __vectors_start + 0x1000 - __stubs_start



	.globl	__vectors_start

__vectors_start:

 ARM(	swi	SYS_ERROR0	)

 THUMB(	svc	#0		)

 THUMB(	nop			)

	W(b)	vector_rst + stubs_offset

	W(b)	vector_und + stubs_offset

	W(ldr)	pc, .LCvswi + stubs_offset

	W(b)	vector_pabt + stubs_offset

arch/arm/kernel/traps.c

+2 −2
Original line number Diff line number Diff line
@@ -837,7 +837,7 @@ void __init early_trap_init(void *vectors_base) 
	 * are visible to the instruction stream.

	 */

	memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);

	memcpy((void *)vectors + 0x200, __stubs_start, __stubs_end - __stubs_start);

	memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);

	memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);



	/*
@@ -852,7 +852,7 @@ void __init early_trap_init(void *vectors_base) 
	memcpy((void *)(vectors + KERN_SIGRETURN_CODE - CONFIG_VECTORS_BASE),

	       sigreturn_codes, sizeof(sigreturn_codes));



	flush_icache_range(vectors, vectors + PAGE_SIZE);

	flush_icache_range(vectors, vectors + PAGE_SIZE * 2);

	modify_domain(DOMAIN_USER, DOMAIN_CLIENT);

#else /* ifndef CONFIG_CPU_V7M */

	/*

arch/arm/mm/mmu.c

+9 −1
Original line number Diff line number Diff line
@@ -1160,7 +1160,7 @@ static void __init devicemaps_init(struct machine_desc *mdesc) 
	/*

	 * Allocate the vector page early.

	 */

	vectors = early_alloc(PAGE_SIZE);

	vectors = early_alloc(PAGE_SIZE * 2);



	early_trap_init(vectors);
@@ -1210,10 +1210,18 @@ static void __init devicemaps_init(struct machine_desc *mdesc) 


	if (!vectors_high()) {

		map.virtual = 0;

		map.length = PAGE_SIZE * 2;

		map.type = MT_LOW_VECTORS;

		create_mapping(&map);

	}



	/* Now create a kernel read-only mapping */

	map.pfn += 1;

	map.virtual = 0xffff0000 + PAGE_SIZE;

	map.length = PAGE_SIZE;

	map.type = MT_LOW_VECTORS;

	create_mapping(&map);



	/*

	 * Ask the machine support to map in the statically mapped devices.

	 */