linux/arch/arm64/lib/copy_from_user.S
James Morse 7054419600 arm64: kernel: Don't toggle PAN on systems with UAO
If a CPU supports both Privileged Access Never (PAN) and User Access
Override (UAO), we don't need to disable/re-enable PAN round all
copy_to_user() like calls.

UAO alternatives cause these calls to use the 'unprivileged' load/store
instructions, which are overridden to be the privileged kind when
fs==KERNEL_DS.

This patch changes the copy_to_user() calls to have their PAN toggling
depend on a new composite 'feature' ARM64_ALT_PAN_NOT_UAO.

If both features are detected, PAN will be enabled, but the copy_to_user()
alternatives will not be applied. This means PAN will be enabled all the
time for these functions. If only PAN is detected, the toggling will be
enabled as normal.

This will save the time taken to disable/re-enable PAN, and allow us to
catch copy_to_user() accesses that occur with fs==KERNEL_DS.

Futex and swp-emulation code continue to hang their PAN toggling code on
ARM64_HAS_PAN.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2016-02-18 17:27:05 +00:00

90 lines
2.0 KiB
ArmAsm

/*
* 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/>.
*/
#include <linux/linkage.h>
#include <asm/alternative.h>
#include <asm/assembler.h>
#include <asm/cache.h>
#include <asm/cpufeature.h>
#include <asm/sysreg.h>
/*
* Copy from user space to a kernel buffer (alignment handled by the hardware)
*
* Parameters:
* x0 - to
* x1 - from
* x2 - n
* Returns:
* x0 - bytes not copied
*/
.macro ldrb1 ptr, regB, val
uao_user_alternative 9998f, ldrb, ldtrb, \ptr, \regB, \val
.endm
.macro strb1 ptr, regB, val
strb \ptr, [\regB], \val
.endm
.macro ldrh1 ptr, regB, val
uao_user_alternative 9998f, ldrh, ldtrh, \ptr, \regB, \val
.endm
.macro strh1 ptr, regB, val
strh \ptr, [\regB], \val
.endm
.macro ldr1 ptr, regB, val
uao_user_alternative 9998f, ldr, ldtr, \ptr, \regB, \val
.endm
.macro str1 ptr, regB, val
str \ptr, [\regB], \val
.endm
.macro ldp1 ptr, regB, regC, val
uao_ldp 9998f, \ptr, \regB, \regC, \val
.endm
.macro stp1 ptr, regB, regC, val
stp \ptr, \regB, [\regC], \val
.endm
end .req x5
ENTRY(__copy_from_user)
ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(0)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
add end, x0, x2
#include "copy_template.S"
ALTERNATIVE("nop", __stringify(SET_PSTATE_PAN(1)), ARM64_ALT_PAN_NOT_UAO, \
CONFIG_ARM64_PAN)
mov x0, #0 // Nothing to copy
ret
ENDPROC(__copy_from_user)
.section .fixup,"ax"
.align 2
9998:
sub x0, end, dst
9999:
strb wzr, [dst], #1 // zero remaining buffer space
cmp dst, end
b.lo 9999b
ret
.previous