- Remove coding standard violations reported by checkpatch.pl
- Delete comment about handling of conditional branches which is no
longer true.
- Delete comment at end of file which lists all ARM instructions. This
duplicates data available in the ARM ARM and seems like an
unnecessary maintenance burden to keep this up to date and accurate.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Being able to probe NOP instructions is useful for hard-coding probeable
locations and is used by the kprobes test code.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
These bit field manipulation instructions occur several thousand
times in an ARMv7 kernel.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The MOVW and MOVT instructions account for approximately 7% of all
instructions in a ARMv7 kernel as GCC uses them instead of a literal
pool.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The instruction decoding in space_cccc_000x needs to reject probing of
instructions with undefined patterns as they may in future become
defined and then emulated faultily - as has already happened with the
SMC instruction.
This fix is achieved by testing for the instruction patterns we want to
probe and making the the default fall-through paths reject probes. This
also allows us to remove some explicit tests for instructions that we
wish to reject, as that is now the default action.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The tests to explicitly reject probing CPS, RFE and SRS instructions
are redundant as the default case is now to reject undecoded patterns.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The PLD instructions wasn't being decoded correctly and the emulation
code wasn't adjusting PC correctly.
As the PLD instruction is only a performance hint we emulate it as a
simple nop, and we can broaden the instruction decoding to take into
account newer PLI and PLDW instructions.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The emulation of SETEND was broken as it changed the endianess for
the running kprobes handling code. Rather than adding a new simulation
routine to fix this we'll just reject probing of SETEND as these should
be very rare in the kernel.
Note, the function emulate_none is now unused but it is left in the
source code as future patches will use it.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Following the change to remove support for coprocessor instructions
we are left with three stub functions which can be consolidated.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The kernel doesn't currently support VFP or Neon code, and probing of
code with CP15 operations is fraught with bad consequences. Therefore we
don't need the ability to probe coprocessor instructions and the code to
support this can be removed.
The removed code also had at least two bugs:
- MRC into R15 should set CPSR not trash PC
- LDC and STC which use PC as base register needed the address offset by 8
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The USAD8 instruction wasn't being explicitly decoded leading
to the incorrect emulation routine being called. It can be correctly
decoded in the same way as the signed multiply instructions so we move
the decoding there.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The signed multiply instructions were being decoded incorrectly.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
These sign extension instructions are encoded as extend-and-add
instructions where the register to add is specified as r15. The decoding
routines weren't checking for this and were using the incorrect
emulation code, giving incorrect results.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The instructions space for media instructions contains some undefined
patterns. We need to reject probing of these because they may in future
become defined and the kprobes code may then emulate them faultily.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The v6T2 RBIT instruction was accidentally being emulated correctly,
this patch adds correct decoding for the instruction.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
These instructions are specified as UNPREDICTABLE.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The decoding of these instructions got the register indexed and
immediate indexed forms the wrong way around, causing incorrect
emulation.
Instructions like "LDRD Rx, [Rx]" were corrupting Rx because the base
register writeback was being performed unconditionally, overwriting the
value just loaded from memory. The fix is to only writeback the base
register when that form of the instruction is used. Note, now that we
reject probing writeback with PC the emulation code doesn't need the
check rn!=15.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Using PC as an base register with writeback is UNPREDICTABLE, as is non
word-sized loads or stores of PC. (We only really care about preventing
loads to PC but it keeps the code simpler if we also exclude stores.)
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The decoding of these instructions got the register indexed and
immediate indexed forms the wrong way around, causing incorrect
emulation.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The emulation code for STREX and LDREX instructions is faulty, however,
rather than attempting to fix this we reject probes of these
instructions. We do this because they can never succeed in gaining
exclusive access as the exception framework clears the exclusivity
monitor when a probes breakpoint is hit. (This is a general problem
when probing all instructions executing between a LDREX and its
corresponding STREX and can lead to infinite retry loops.)
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The instructions space for 'Multiply and multiply-accumulate'
instructions contains some undefined patterns. We need to reject
probing of these because they may in future become defined and the
kprobes code may then emulate them faultily.
This has already happened with the new MLS instruction which this patch
also adds correct decoding for as well as tightening up other decoding
tests. (Before this patch the wrong emulation routine was being called
for MLS though it still produced correct results.)
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The MRS instruction should set mode and interrupt bits in the read value
so it is simpler to use a new simulation routine (simulate_mrs) rather
than some modified emulation.
prep_emulate_rd12 is now unused and removed.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
We need to reject probing of instructions which read SPSR because
we can't handle this as the value in SPSR is lost when the exception
handler for the probe breakpoint first runs.
This patch also fixes the bitmask for MRS instructions decoding to
include checking bits 5-7.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Emulation of instructions like "ADD rd, rn, #<const>" would result in a
corrupted value for rd.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Probing these instructions was corrupting R0 because the emulation code
didn't account for the fact that they don't write a result to a
register.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Now we have the framework code handling conditionally executed
instructions we can remove redundant checks in individual simulation
routines.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
When a kprobe is placed onto conditionally executed ARM instructions,
many of the emulation routines used to single step them produce corrupt
register results. Rather than fix all of these cases we modify the
framework which calls them to test the relevant condition flags and, if
the test fails, skip calling the emulation code.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Currently emulate_ldrd and emulate_strd don't even have the adjustment
of the PC value, so in case of Rn == PC, it will not update the PC
incorrectly but instead load/store from the wrong address. Let's add
both the adjustment of the PC value and the check for PC == PC.
Signed-off-by: Viktor Rosendahl <viktor.rosendahl@nokia.com>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
The Rn value from the emulation is unconditionally written back;
this is fine as long as Rn != PC because in that case, even if the
instruction isn't a write back instruction, it will only result in the
same value being written back.
In case Rn == PC, then the emulated instruction doesn't have the
actual PC value in Rn but an adjusted value; when this is written
back, it will result in the PC being incorrectly updated.
An altenative solution would be to check bits 24 and 22 to see whether
the instruction actually is a write back instruction or not. I think
it's enough to check whether Rn != PC, because:
- it's looks cheaper than the alternative
- to my understaning it's not permitted to update the PC with a write
back instruction, so we don't lose any ability to emulate legal
instructions.
- in case of writing back for non write back instructions where Rn != PC, it doesn't matter because the values are the same.
Regarding the second point above, it would possibly be prudent to add
some checking to prep_emulate_ldr_str(), so that instructions with
both write back and Rn == PC would be rejected.
Signed-off-by: Viktor Rosendahl <viktor.rosendahl@nokia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Marcin Slusarz says:
> In arch/arm/kernel/kprobes-decode.c there's a function
> arm_kprobe_decode_insn which does:
>
> } else if ((insn & 0x0e000000) == 0x0c400000) {
> ...
>
> This is always false, so code below is dead.
> I found this bug by coccinelle (http://coccinelle.lip6.fr/).
Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
The MOVW instruction moves a 16-bit immediate into the bottom halfword
of the destination register.
This patch ensures that kprobes leaves the 16-bit immediate intact, rather
than assume a 12-bit immediate and mask out the upper 4 bits.
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
From: Bin Yang <bin.yang@marvell.com>
Cc: stable@kernel.org
Signed-off-by: Bin Yang <bin.yang@marvell.com>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
The ARM kprobes arithmetic immediate instruction decoder
(space_cccc_001x()) was accidentally zero'ing out not only the Rn and
Rd arguments, but the lower nibble of the immediate argument as well
-- this patch fixes this.
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Nicolas Pitre <nico@marvell.com>
This is the code implementing instruction single-stepping for kprobes
on ARM.
To get around the limitation of no Next-PC and no hardware single-
stepping, all kprobe'd instructions are split into three camps:
simulation, emulation, and rejected. "Simulated" instructions are
those instructions which behavior is reproduced by straight C code.
"Emulated" instructions are ones that are copied, slightly altered
and executed directly in the instruction slot to reproduce their
behavior. "Rejected" instructions are ones that could be simulated,
but work hasn't been put into simulating them. These instructions
should be very rare, if not unencountered, in the kernel. If ever
needed, code could be added to simulate them.
One might wonder why this and the ptrace singlestep facility are not
sharing some code. Both approaches are fundamentally different because
the ptrace code regains control after the stepped instruction by installing
a breakpoint after the instruction itself, and possibly at the location
where the instruction might be branching to, instead of simulating or
emulating the target instruction.
The ptrace approach isn't suitable for kprobes because the breakpoints
would have to be moved back, and the icache flushed, everytime the
probe is hit to let normal code execution resume, which would have a
significant performance impact. It is also racy on SMP since another
CPU could, with the right timing, sail through the probe point without
being caught. Because ptrace single-stepping always result in a
different process to be scheduled, the concern for performance is much
less significant.
On the other hand, the kprobes approach isn't (currently) suitable for
ptrace because it has no provision for proper user space memory
protection and translation, and even if that was implemented, the gain
wouldn't be worth the added complexity in the ptrace path compared to
the current approach.
So, until kprobes does support user space, both kprobes and ptrace are
best kept independent and separate.
Signed-off-by: Quentin Barnes <qbarnes@gmail.com>
Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>
Jon Medhurst
Viktor Rosendahl
Nicolas Pitre
Will Deacon
Nicolas Pitre
Nicolas Pitre
Lennert Buytenhek
Quentin Barnes