Commit 51369e39 authored by Robin Murphy's avatar Robin Murphy Committed by Catalin Marinas
Browse files

arm64: Make USER_DS an inclusive limit 



Currently, USER_DS represents an exclusive limit while KERNEL_DS is
inclusive. In order to do some clever trickery for speculation-safe
masking, we need them both to behave equivalently - there aren't enough
bits to make KERNEL_DS exclusive, so we have precisely one option. This
also happens to correct a longstanding false negative for a range
ending on the very top byte of kernel memory.

Mark Rutland points out that we've actually got the semantics of
addresses vs. segments muddled up in most of the places we need to
amend, so shuffle the {USER,KERNEL}_DS definitions around such that we
can correct those properly instead of just pasting "-1"s everywhere.

Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 022620ee

arch/arm64/include/asm/processor.h

+3 −0
Original line number Diff line number Diff line
@@ -21,6 +21,9 @@ 


#define TASK_SIZE_64		(UL(1) << VA_BITS)



#define KERNEL_DS	UL(-1)

#define USER_DS		(TASK_SIZE_64 - 1)



#ifndef __ASSEMBLY__



/*

arch/arm64/include/asm/uaccess.h

+26 −19
Original line number Diff line number Diff line
@@ -35,10 +35,7 @@ 
#include <asm/compiler.h>

#include <asm/extable.h>



#define KERNEL_DS	(-1UL)

#define get_ds()	(KERNEL_DS)



#define USER_DS		TASK_SIZE_64

#define get_fs()	(current_thread_info()->addr_limit)



static inline void set_fs(mm_segment_t fs)
@@ -66,22 +63,32 @@ static inline void set_fs(mm_segment_t fs) 
 * Returns 1 if the range is valid, 0 otherwise.

 *

 * This is equivalent to the following test:

 * (u65)addr + (u65)size <= current->addr_limit

 *

 * This needs 65-bit arithmetic.

 * (u65)addr + (u65)size <= (u65)current->addr_limit + 1

 */

#define __range_ok(addr, size)						\

({									\

	unsigned long __addr = (unsigned long)(addr);			\

	unsigned long flag, roksum;					\

	__chk_user_ptr(addr);						\

	asm("adds %1, %1, %3; ccmp %1, %4, #2, cc; cset %0, ls"		\

		: "=&r" (flag), "=&r" (roksum)				\

		: "1" (__addr), "Ir" (size),				\

		  "r" (current_thread_info()->addr_limit)		\

		: "cc");						\

	flag;								\

})

static inline unsigned long __range_ok(unsigned long addr, unsigned long size)

{

	unsigned long limit = current_thread_info()->addr_limit;



	__chk_user_ptr(addr);

	asm volatile(

	// A + B <= C + 1 for all A,B,C, in four easy steps:

	// 1: X = A + B; X' = X % 2^64

	"	adds	%0, %0, %2\n"

	// 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4

	"	csel	%1, xzr, %1, hi\n"

	// 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'

	//    to compensate for the carry flag being set in step 4. For

	//    X > 2^64, X' merely has to remain nonzero, which it does.

	"	csinv	%0, %0, xzr, cc\n"

	// 4: For X < 2^64, this gives us X' - C - 1 <= 0, where the -1

	//    comes from the carry in being clear. Otherwise, we are

	//    testing X' - C == 0, subject to the previous adjustments.

	"	sbcs	xzr, %0, %1\n"

	"	cset	%0, ls\n"

	: "+r" (addr), "+r" (limit) : "Ir" (size) : "cc");



	return addr;

}



/*

 * When dealing with data aborts, watchpoints, or instruction traps we may end
@@ -90,7 +97,7 @@ static inline void set_fs(mm_segment_t fs) 
 */

#define untagged_addr(addr)		sign_extend64(addr, 55)



#define access_ok(type, addr, size)	__range_ok(addr, size)

#define access_ok(type, addr, size)	__range_ok((unsigned long)(addr), size)

#define user_addr_max			get_fs



#define _ASM_EXTABLE(from, to)						\

arch/arm64/kernel/entry.S

+2 −2
Original line number Diff line number Diff line
@@ -167,10 +167,10 @@ alternative_else_nop_endif 
	.else

	add	x21, sp, #S_FRAME_SIZE

	get_thread_info tsk

	/* Save the task's original addr_limit and set USER_DS (TASK_SIZE_64) */

	/* Save the task's original addr_limit and set USER_DS */

	ldr	x20, [tsk, #TSK_TI_ADDR_LIMIT]

	str	x20, [sp, #S_ORIG_ADDR_LIMIT]

	mov	x20, #TASK_SIZE_64

	mov	x20, #USER_DS

	str	x20, [tsk, #TSK_TI_ADDR_LIMIT]

	/* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */

	.endif /* \el == 0 */

arch/arm64/mm/fault.c

+2 −2
Original line number Diff line number Diff line
@@ -240,7 +240,7 @@ static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs, 
	if (fsc_type == ESR_ELx_FSC_PERM)

		return true;



	if (addr < USER_DS && system_uses_ttbr0_pan())

	if (addr < TASK_SIZE && system_uses_ttbr0_pan())

		return fsc_type == ESR_ELx_FSC_FAULT &&

			(regs->pstate & PSR_PAN_BIT);
@@ -414,7 +414,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, 
		mm_flags |= FAULT_FLAG_WRITE;

	}



	if (addr < USER_DS && is_permission_fault(esr, regs, addr)) {

	if (addr < TASK_SIZE && is_permission_fault(esr, regs, addr)) {

		/* regs->orig_addr_limit may be 0 if we entered from EL0 */

		if (regs->orig_addr_limit == KERNEL_DS)

			die("Accessing user space memory with fs=KERNEL_DS", regs, esr);

CRA Git | Maintained and supported by SUSTech CRA and CCSE