arch/arm64/include/asm/uaccess.h

/*
 * Based on arch/arm/include/asm/uaccess.h
 *
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef __ASM_UACCESS_H
#define __ASM_UACCESS_H

#include <asm/alternative.h>
#include <asm/kernel-pgtable.h>
#include <asm/mmu.h>
#include <asm/sysreg.h>

#ifndef __ASSEMBLY__

/*
 * User space memory access functions
 */
#include <linux/bitops.h>
#include <linux/kasan-checks.h>
#include <linux/string.h>
#include <linux/thread_info.h>

#include <asm/cpufeature.h>
#include <asm/processor.h>
#include <asm/ptrace.h>
#include <asm/errno.h>
#include <asm/memory.h>
#include <asm/compiler.h>

#define VERIFY_READ 0
#define VERIFY_WRITE 1

/*
 * The exception table consists of pairs of relative offsets: the first
 * is the relative offset to an instruction that is allowed to fault,
 * and the second is the relative offset at which the program should
 * continue. No registers are modified, so it is entirely up to the
 * continuation code to figure out what to do.
 *
 * All the routines below use bits of fixup code that are out of line
 * with the main instruction path.  This means when everything is well,
 * we don't even have to jump over them.  Further, they do not intrude
 * on our cache or tlb entries.
 */

struct exception_table_entry
{
	int insn, fixup;
};

#define ARCH_HAS_RELATIVE_EXTABLE

extern int fixup_exception(struct pt_regs *regs);

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

static inline void set_fs(mm_segment_t fs)
{
	current_thread_info()->addr_limit = fs;

	/* On user-mode return, check fs is correct */
	set_thread_flag(TIF_FSCHECK);

	/*
	 * Prevent a mispredicted conditional call to set_fs from forwarding
	 * the wrong address limit to access_ok under speculation.
	 */
	dsb(nsh);
	isb();

	/*
	 * Enable/disable UAO so that copy_to_user() etc can access
	 * kernel memory with the unprivileged instructions.
	 */
	if (IS_ENABLED(CONFIG_ARM64_UAO) && fs == KERNEL_DS)
		asm(ALTERNATIVE("nop", SET_PSTATE_UAO(1), ARM64_HAS_UAO));
	else
		asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO,
				CONFIG_ARM64_UAO));
}

#define segment_eq(a, b)	((a) == (b))

/*
 * Test whether a block of memory is a valid user space address.
 * Returns 1 if the range is valid, 0 otherwise.
 *
 * This is equivalent to the following test:
 * (u65)addr + (u65)size <= (u65)current->addr_limit + 1
 */
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
 * up with a tagged userland pointer. Clear the tag to get a sane pointer to
 * pass on to access_ok(), for instance.
 */
#define untagged_addr(addr)		sign_extend64(addr, 55)

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

#define _ASM_EXTABLE(from, to)						\
	"	.pushsection	__ex_table, \"a\"\n"			\
	"	.align		3\n"					\
	"	.long		(" #from " - .), (" #to " - .)\n"	\
	"	.popsection\n"

/*
 * User access enabling/disabling.
 */
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
static inline void __uaccess_ttbr0_disable(void)
{
	unsigned long flags, ttbr;

	local_irq_save(flags);
	ttbr = read_sysreg(ttbr1_el1);
	ttbr &= ~TTBR_ASID_MASK;
	/* reserved_ttbr0 placed at the end of swapper_pg_dir */
	write_sysreg(ttbr + SWAPPER_DIR_SIZE, ttbr0_el1);
	isb();
	/* Set reserved ASID */
	write_sysreg(ttbr, ttbr1_el1);
	isb();
	local_irq_restore(flags);
}

static inline void __uaccess_ttbr0_enable(void)
{
	unsigned long flags, ttbr0, ttbr1;

	/*
	 * Disable interrupts to avoid preemption between reading the 'ttbr0'
	 * variable and the MSR. A context switch could trigger an ASID
	 * roll-over and an update of 'ttbr0'.
	 */
	local_irq_save(flags);
	ttbr0 = READ_ONCE(current_thread_info()->ttbr0);

	/* Restore active ASID */
	ttbr1 = read_sysreg(ttbr1_el1);
	ttbr1 &= ~TTBR_ASID_MASK;		/* safety measure */
	ttbr1 |= ttbr0 & TTBR_ASID_MASK;
	write_sysreg(ttbr1, ttbr1_el1);
	isb();

	/* Restore user page table */
	write_sysreg(ttbr0, ttbr0_el1);
	isb();
	local_irq_restore(flags);
}

static inline bool uaccess_ttbr0_disable(void)
{
	if (!system_uses_ttbr0_pan())
		return false;
	__uaccess_ttbr0_disable();
	return true;
}

static inline bool uaccess_ttbr0_enable(void)
{
	if (!system_uses_ttbr0_pan())
		return false;
	__uaccess_ttbr0_enable();
	return true;
}
#else
static inline bool uaccess_ttbr0_disable(void)
{
	return false;
}

static inline bool uaccess_ttbr0_enable(void)
{
	return false;
}
#endif

#define __uaccess_disable(alt)						\
do {									\
	if (!uaccess_ttbr0_disable())					\
		asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), alt,		\
				CONFIG_ARM64_PAN));			\
} while (0)

#define __uaccess_enable(alt)						\
do {									\
	if (!uaccess_ttbr0_enable())					\
		asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), alt,		\
				CONFIG_ARM64_PAN));			\
} while (0)

static inline void uaccess_disable(void)
{
	__uaccess_disable(ARM64_HAS_PAN);
}

static inline void uaccess_enable(void)
{
	__uaccess_enable(ARM64_HAS_PAN);
}

/*
 * These functions are no-ops when UAO is present.
 */
static inline void uaccess_disable_not_uao(void)
{
	__uaccess_disable(ARM64_ALT_PAN_NOT_UAO);
}

static inline void uaccess_enable_not_uao(void)
{
	__uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
}

/*
 * Sanitise a uaccess pointer such that it becomes NULL if above the
 * current addr_limit.
 */
#define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
{
	void __user *safe_ptr;

	asm volatile(
	"	bics	xzr, %1, %2\n"
	"	csel	%0, %1, xzr, eq\n"
	: "=&r" (safe_ptr)
	: "r" (ptr), "r" (current_thread_info()->addr_limit)
	: "cc");

	csdb();
	return safe_ptr;
}

/*
 * The "__xxx" versions of the user access functions do not verify the address
 * space - it must have been done previously with a separate "access_ok()"
 * call.
 *
 * The "__xxx_error" versions set the third argument to -EFAULT if an error
 * occurs, and leave it unchanged on success.
 */
#define __get_user_asm(instr, alt_instr, reg, x, addr, err, feature)	\
	asm volatile(							\
	"1:"ALTERNATIVE(instr "     " reg "1, [%2]\n",			\
			alt_instr " " reg "1, [%2]\n", feature)		\
	"2:\n"								\
	"	.section .fixup, \"ax\"\n"				\
	"	.align	2\n"						\
	"3:	mov	%w0, %3\n"					\
	"	mov	%1, #0\n"					\
	"	b	2b\n"						\
	"	.previous\n"						\
	_ASM_EXTABLE(1b, 3b)						\
	: "+r" (err), "=&r" (x)						\
	: "r" (addr), "i" (-EFAULT))

#define __get_user_err(x, ptr, err)					\
do {									\
	unsigned long __gu_val;						\
	__chk_user_ptr(ptr);						\
	uaccess_enable_not_uao();					\
	switch (sizeof(*(ptr))) {					\
	case 1:								\
		__get_user_asm("ldrb", "ldtrb", "%w", __gu_val, (ptr),  \
			       (err), ARM64_HAS_UAO);			\
		break;							\
	case 2:								\
		__get_user_asm("ldrh", "ldtrh", "%w", __gu_val, (ptr),  \
			       (err), ARM64_HAS_UAO);			\
		break;							\
	case 4:								\
		__get_user_asm("ldr", "ldtr", "%w", __gu_val, (ptr),	\
			       (err), ARM64_HAS_UAO);			\
		break;							\
	case 8:								\
		__get_user_asm("ldr", "ldtr", "%x",  __gu_val, (ptr),	\
			       (err), ARM64_HAS_UAO);			\
		break;							\
	default:							\
		BUILD_BUG();						\
	}								\
	uaccess_disable_not_uao();					\
	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
} while (0)

#define __get_user_check(x, ptr, err)					\
({									\
	__typeof__(*(ptr)) __user *__p = (ptr);				\
	might_fault();							\
	if (access_ok(VERIFY_READ, __p, sizeof(*__p))) {		\
		__p = uaccess_mask_ptr(__p);				\
		__get_user_err((x), __p, (err));			\
	} else {							\
		(x) = 0; (err) = -EFAULT;				\
	}								\
})

#define __get_user_error(x, ptr, err)					\
({									\
	__get_user_check((x), (ptr), (err));				\
	(void)0;							\
})

#define __get_user(x, ptr)						\
({									\
	int __gu_err = 0;						\
	__get_user_check((x), (ptr), __gu_err);				\
	__gu_err;							\
})

#define __get_user_unaligned __get_user

#define get_user	__get_user

#define __put_user_asm(instr, alt_instr, reg, x, addr, err, feature)	\
	asm volatile(							\
	"1:"ALTERNATIVE(instr "     " reg "1, [%2]\n",			\
			alt_instr " " reg "1, [%2]\n", feature)		\
	"2:\n"								\
	"	.section .fixup,\"ax\"\n"				\
	"	.align	2\n"						\
	"3:	mov	%w0, %3\n"					\
	"	b	2b\n"						\
	"	.previous\n"						\
	_ASM_EXTABLE(1b, 3b)						\
	: "+r" (err)							\
	: "r" (x), "r" (addr), "i" (-EFAULT))

#define __put_user_err(x, ptr, err)					\
do {									\
	__typeof__(*(ptr)) __pu_val = (x);				\
	__chk_user_ptr(ptr);						\
	uaccess_enable_not_uao();					\
	switch (sizeof(*(ptr))) {					\
	case 1:								\
		__put_user_asm("strb", "sttrb", "%w", __pu_val, (ptr),	\
			       (err), ARM64_HAS_UAO);			\
		break;							\
	case 2:								\
		__put_user_asm("strh", "sttrh", "%w", __pu_val, (ptr),	\
			       (err), ARM64_HAS_UAO);			\
		break;							\
	case 4:								\
		__put_user_asm("str", "sttr", "%w", __pu_val, (ptr),	\
			       (err), ARM64_HAS_UAO);			\
		break;							\
	case 8:								\
		__put_user_asm("str", "sttr", "%x", __pu_val, (ptr),	\
			       (err), ARM64_HAS_UAO);			\
		break;							\
	default:							\
		BUILD_BUG();						\
	}								\
	uaccess_disable_not_uao();					\
} while (0)

#define __put_user_check(x, ptr, err)					\
({									\
	__typeof__(*(ptr)) __user *__p = (ptr);				\
	might_fault();							\
	if (access_ok(VERIFY_WRITE, __p, sizeof(*__p))) {		\
		__p = uaccess_mask_ptr(__p);				\
		__put_user_err((x), __p, (err));			\
	} else	{							\
		(err) = -EFAULT;					\
	}								\
})

#define __put_user_error(x, ptr, err)					\
({									\
	__put_user_check((x), (ptr), (err));				\
	(void)0;							\
})

#define __put_user(x, ptr)						\
({									\
	int __pu_err = 0;						\
	__put_user_check((x), (ptr), __pu_err);				\
	__pu_err;							\
})

#define __put_user_unaligned __put_user

#define put_user	__put_user

extern unsigned long __must_check __arch_copy_from_user(void *to, const void __user *from, unsigned long n);
extern unsigned long __must_check __arch_copy_to_user(void __user *to, const void *from, unsigned long n);
extern unsigned long __must_check __arch_copy_in_user(void __user *to, const void __user *from, unsigned long n);

static inline unsigned long __must_check __copy_from_user(void *to, const void __user *from, unsigned long n)
{
	kasan_check_write(to, n);
	check_object_size(to, n, false);
	return __arch_copy_from_user(to, __uaccess_mask_ptr(from), n);
}

static inline unsigned long __must_check __copy_to_user(void __user *to, const void *from, unsigned long n)
{
	kasan_check_read(from, n);
	check_object_size(from, n, true);
	return __arch_copy_to_user(__uaccess_mask_ptr(to), from, n);
}

static inline unsigned long __must_check copy_from_user(void *to, const void __user *from, unsigned long n)
{
	unsigned long res = n;
	kasan_check_write(to, n);

	if (access_ok(VERIFY_READ, from, n)) {
		check_object_size(to, n, false);
		res = __arch_copy_from_user(to, from, n);
	}
	if (unlikely(res))
		memset(to + (n - res), 0, res);
	return res;
}

static inline unsigned long __must_check copy_to_user(void __user *to, const void *from, unsigned long n)
{
	kasan_check_read(from, n);

	if (access_ok(VERIFY_WRITE, to, n)) {
		check_object_size(from, n, true);
		n = __arch_copy_to_user(to, from, n);
	}
	return n;
}

static inline unsigned long __must_check __copy_in_user(void __user *to, const void __user *from, unsigned long n)
{
	if (access_ok(VERIFY_READ, from, n) && access_ok(VERIFY_WRITE, to, n))
		n = __arch_copy_in_user(__uaccess_mask_ptr(to), __uaccess_mask_ptr(from), n);
	return n;
}
#define copy_in_user __copy_in_user

#define __copy_to_user_inatomic __copy_to_user
#define __copy_from_user_inatomic __copy_from_user

extern unsigned long __must_check __arch_clear_user(void __user *to, unsigned long n);
static inline unsigned long __must_check __clear_user(void __user *to, unsigned long n)
{
	if (access_ok(VERIFY_WRITE, to, n))
		n = __arch_clear_user(__uaccess_mask_ptr(to), n);
	return n;
}
#define clear_user	__clear_user

extern long strncpy_from_user(char *dest, const char __user *src, long count);

extern __must_check long strlen_user(const char __user *str);
extern __must_check long strnlen_user(const char __user *str, long n);

#else	/* __ASSEMBLY__ */

#include <asm/assembler.h>

/*
 * User access enabling/disabling macros.
 */
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
	.macro	__uaccess_ttbr0_disable, tmp1
	mrs	\tmp1, ttbr1_el1		// swapper_pg_dir
	bic     \tmp1, \tmp1, #TTBR_ASID_MASK
	add	\tmp1, \tmp1, #SWAPPER_DIR_SIZE	// reserved_ttbr0 at the end of swapper_pg_dir
	msr	ttbr0_el1, \tmp1		// set reserved TTBR0_EL1
	isb
	sub     \tmp1, \tmp1, #SWAPPER_DIR_SIZE
	msr     ttbr1_el1, \tmp1                // set reserved ASID
	isb
	.endm

	.macro	__uaccess_ttbr0_enable, tmp1, tmp2
	get_thread_info \tmp1
	ldr	\tmp1, [\tmp1, #TSK_TI_TTBR0]	// load saved TTBR0_EL1
	mrs     \tmp2, ttbr1_el1
	extr    \tmp2, \tmp2, \tmp1, #48
	ror     \tmp2, \tmp2, #16
	msr     ttbr1_el1, \tmp2                // set the active ASID
	isb
	msr	ttbr0_el1, \tmp1		// set the non-PAN TTBR0_EL1
	isb
	.endm

	.macro	uaccess_ttbr0_disable, tmp1, tmp2
alternative_if_not ARM64_HAS_PAN
	save_and_disable_irq \tmp2		// avoid preemption
	__uaccess_ttbr0_disable \tmp1
	restore_irq \tmp2
alternative_else_nop_endif
	.endm

	.macro	uaccess_ttbr0_enable, tmp1, tmp2, tmp3
alternative_if_not ARM64_HAS_PAN
	save_and_disable_irq \tmp3		// avoid preemption
	__uaccess_ttbr0_enable \tmp1, \tmp2
	restore_irq \tmp3
alternative_else_nop_endif
	.endm
#else
	.macro	uaccess_ttbr0_disable, tmp1, tmp2
	.endm

	.macro	uaccess_ttbr0_enable, tmp1, tmp2, tmp3
	.endm
#endif

/*
 * These macros are no-ops when UAO is present.
 */
	.macro	uaccess_disable_not_uao, tmp1, tmp2
	uaccess_ttbr0_disable \tmp1, \tmp2
alternative_if ARM64_ALT_PAN_NOT_UAO
	SET_PSTATE_PAN(1)
alternative_else_nop_endif
	.endm

	.macro	uaccess_enable_not_uao, tmp1, tmp2, tmp3
	uaccess_ttbr0_enable \tmp1, \tmp2, \tmp3
alternative_if ARM64_ALT_PAN_NOT_UAO
	SET_PSTATE_PAN(0)
alternative_else_nop_endif
	.endm

#endif	/* __ASSEMBLY__ */

#endif /* __ASM_UACCESS_H */