linux/arch/arm/mm/abort-macro.S
Russell King 2190fed67b ARM: entry: provide uaccess assembly macro hooks
Provide hooks into the kernel entry and exit paths to permit control
of userspace visibility to the kernel.  The intended use is:

- on entry to kernel from user, uaccess_disable will be called to
  disable userspace visibility
- on exit from kernel to user, uaccess_enable will be called to
  enable userspace visibility
- on entry from a kernel exception, uaccess_save_and_disable will be
  called to save the current userspace visibility setting, and disable
  access
- on exit from a kernel exception, uaccess_restore will be called to
  restore the userspace visibility as it was before the exception
  occurred.

These hooks allows us to keep userspace visibility disabled for the
vast majority of the kernel, except for localised regions where we
want to explicitly access userspace.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2015-08-26 20:27:02 +01:00

39 lines
1.1 KiB
ArmAsm

/*
* The ARM LDRD and Thumb LDRSB instructions use bit 20/11 (ARM/Thumb)
* differently than every other instruction, so it is set to 0 (write)
* even though the instructions are read instructions. This means that
* during an abort the instructions will be treated as a write and the
* handler will raise a signal from unwriteable locations if they
* fault. We have to specifically check for these instructions
* from the abort handlers to treat them properly.
*
*/
.macro do_thumb_abort, fsr, pc, psr, tmp
tst \psr, #PSR_T_BIT
beq not_thumb
ldrh \tmp, [\pc] @ Read aborted Thumb instruction
uaccess_disable ip @ disable userspace access
and \tmp, \tmp, # 0xfe00 @ Mask opcode field
cmp \tmp, # 0x5600 @ Is it ldrsb?
orreq \tmp, \tmp, #1 << 11 @ Set L-bit if yes
tst \tmp, #1 << 11 @ L = 0 -> write
orreq \fsr, \fsr, #1 << 11 @ yes.
b do_DataAbort
not_thumb:
.endm
/*
* We check for the following instruction encoding for LDRD.
*
* [27:25] == 000
* [7:4] == 1101
* [20] == 0
*/
.macro teq_ldrd, tmp, insn
mov \tmp, #0x0e100000
orr \tmp, #0x000000f0
and \tmp, \insn, \tmp
teq \tmp, #0x000000d0
.endm