[PATCH 2/3] ARM: kprobes: Disallow instructions with PC and register specified shift

[tixy@linaro.org (Jon Medhurst (Tixy))]

On Mon, 2014-03-24 at 15:49 -0400, David Long wrote:
> On 03/11/14 12:54, Jon Medhurst wrote:
> > ARM data processing instructions which have a register specified shift
> > are defined as UNPREDICTABLE if PC is used for any register, not just
> > the shift value as the code was previous assuming. This issue manifests
> > on A15 devices as either test case failures or undefined instructions
> > aborts.
> >
> > Reported-by: David Long <dave.long@linaro.org>
> > Signed-off-by: Jon Medhurst <tixy@linaro.org>
> > ---
> >   arch/arm/kernel/kprobes-test-arm.c |   25 +++++++++++++------------
> >   arch/arm/kernel/probes-arm.c       |    6 +++---
> >   2 files changed, 16 insertions(+), 15 deletions(-)
> >
> > diff --git a/arch/arm/kernel/kprobes-test-arm.c b/arch/arm/kernel/kprobes-test-arm.c
> > index 87839de..8a7428b 100644
> > --- a/arch/arm/kernel/kprobes-test-arm.c
> > +++ b/arch/arm/kernel/kprobes-test-arm.c
> > @@ -73,12 +73,9 @@ void kprobe_arm_test_cases(void)
> >   	TEST_RRR( op "lt" s "	r11, r",11,VAL1,", r",14,N(val),", asr r",7, 6,"")\
> >   	TEST_RR(  op "gt" s "	r12, r13"       ", r",14,val, ", ror r",14,7,"")\
> >   	TEST_RR(  op "le" s "	r14, r",0, val, ", r13"       ", lsl r",14,8,"")\
> > -	TEST_RR(  op s "	r12, pc"        ", r",14,val, ", ror r",14,7,"")\
> > -	TEST_RR(  op s "	r14, r",0, val, ", pc"        ", lsl r",14,8,"")\
> >   	TEST_R(   op "eq" s "	r0,  r",11,VAL1,", #0xf5")			\
> >   	TEST_R(   op "ne" s "	r11, r",0, VAL1,", #0xf5000000")		\
> > -	TEST_R(   op s "	r7,  r",8, VAL2,", #0x000af000")		\
> > -	TEST(     op s "	r4,  pc"        ", #0x00005a00")
> 
> The last two lines above confuse me.  Can you explain why those needed 
> to be removed?  Is there somehow a shift involved with those instructions?
> 
> The rest looked OK to me.  I'm omitting it for the sake of brevity.

The next line in the patch was

+	TEST_R(   op s "	r7,  r",8, VAL2,", #0x000af000")

so the change actually only removed the last test case. However, as you
say, this doesn't involve a shift by a register and so shouldn't have
been removed by this patch, I'll fix that. Thanks for spotting the
error.

-- 
Tixy