by Jon Medhurst (Tixy)

[permalink] [raw]

Subject: Re: [PATCH v3] ARM: kprobes: Add test cases for stack consuming instructions

On Wed, 2014-12-10 at 21:18 +0800, Wang Nan wrote:
[...]
> Well, I'm just working on a patch which introducing a TEST_INTOFF and disable interrupts
> for "MRS" testcase. Do you think it is inappropriate?

That's what I started to do, implementing in a similar way to
DONT_TEST_IN_ITBLOCK, and thought the same ints off feature could be
used for the stack consuming instructions checks as well.

Then I realised that for the MRS case it's no use turning ints off for a
single iteration of a test, because the next iteration could see
different results, so that would mean turning interrupts off for all
iterations, which we can't do.

Also, the FIQ flag may not be under our control if Linux isn't running
in secure mode, and I was worried that in such cases we could see the
value of the flag change if secure mode code chose to do so. (Though
perhaps non-secure mode will always read FIQ flag as zero in such a
case?)

So in the end I thought the only robust way of writing the tests would
be to ignore the values of the A and F flags.

--
Tixy

2014-12-11 09:57:41

by Wang Nan

[permalink] [raw]

Subject: Re: [PATCH v3] ARM: kprobes: Add test cases for stack consuming instructions

On 2014/12/10 21:18, Wang Nan wrote:
> On 2014/12/10 20:34, Jon Medhurst (Tixy) wrote:
>> On Wed, 2014-12-10 at 16:23 +0800, Wang Nan wrote:
>>> Hi Tixy,
>>>
>>> I experienced another FAIL during test:
>>>
>>> [11567.220477] Miscellaneous instructions
>>> [11567.265397] ---------------------------------------------------------
>>> [11567.342626] mrs r0, cpsr @ e10f0000
>>> [11568.612656] FAIL: registers differ
>>> [11568.653414] FAIL: Test mrs r0, cpsr
>>> [11568.695210] FAIL: Scenario 5
>>> [11568.729709] initial_regs:
>>> [11568.761083] r0 21522152 | r1 21522052 | r2 21522352 | r3 21522252
>>> [11568.838301] r4 21522552 | r5 21522452 | r6 21522752 | r7 21522652
>>> [11568.915526] r8 21522952 | r9 21522852 | r10 21522b52 | r11 21522a52
>>> [11568.992748] r12 21522d52 | sp ed343cf0 | lr 21522f52 | pc bf11f590
>>> [11569.069969] cpsr 58050013
>>> [11569.101336] expected_regs:
>>> [11569.133750] r0 58050013 | r1 21522052 | r2 21522352 | r3 21522252
>>> [11569.210975] r4 21522552 | r5 21522452 | r6 21522752 | r7 21522652
>>> [11569.288197] r8 21522952 | r9 21522852 | r10 21522b52 | r11 21522a52
>>> [11569.365417] r12 21522d52 | sp ed343cf0 | lr 21522f52 | pc bf11f594
>>> [11569.442634] cpsr 58050013
>>> [11569.474010] result_regs:
>>> [11569.504337] r0 58050113 | r1 21522052 | r2 21522352 | r3 21522252 <--- see R0 in this line
>>> [11569.581556] r4 21522552 | r5 21522452 | r6 21522752 | r7 21522652
>>> [11569.658776] r8 21522952 | r9 21522852 | r10 21522b52 | r11 21522a52
>>> [11569.736000] r12 21522d52 | sp ed343cf0 | lr 21522f52 | pc bf11f594
>>> [11569.813222] cpsr 58050013
>>> [11569.844593] mrspl r7, cpsr @ 510f7000
>>> [11571.842652] mrs r14, cpsr @ e10fe000
>>>
>>> The failure is raise when testing in "mrs r0, cpsr". The added bit is PSR_A_BIT, which
>>> should be ignored.
>>>
>>> So looks like this is also a problem in your test framework. If you don't have
>>> enough time, you can give me some hints to deal with it.
>>
>> The problem is that the A bit can change randomly when interrupts or
>> reschedules happen (I'm not sure it should, and it may be a bug). For
>> the purposes of this test code, we can't disable interrupts and
>> scheduling around all the iterations of a test case, because inserting
>> and removing probes requires them to be enabled. So we need a method of
>> ignoring bits in cpsr, how about the following patch...
>>
>> ----------------------------------------------------------------------------
>>
>> From: Jon Medhurst <[email protected]>
>> Subject: [PATCH] ARM: kprobes: Fix unreliable MRS instruction tests
>>
>> For the instruction 'mrs Rn, cpsr' the resulting value of Rn can vary due to
>> external factors we can't control. So get the test code to mask out these
>> indeterminate bits.
>>
>> Signed-off-by: Jon Medhurst <[email protected]>
>> ---
>> arch/arm/probes/kprobes/test-arm.c | 6 +++---
>> arch/arm/probes/kprobes/test-core.c | 19 ++++++++++---------
>> arch/arm/probes/kprobes/test-core.h | 33 ++++++++++++++++++++++++++++-----
>> arch/arm/probes/kprobes/test-thumb.c | 4 ++--
>> 4 files changed, 43 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/arm/probes/kprobes/test-arm.c b/arch/arm/probes/kprobes/test-arm.c
>> index 9b3b1b4..e72b07e 100644
>> --- a/arch/arm/probes/kprobes/test-arm.c
>> +++ b/arch/arm/probes/kprobes/test-arm.c
>> @@ -204,9 +204,9 @@ void kprobe_arm_test_cases(void)
>> #endif
>> TEST_GROUP("Miscellaneous instructions")
>>
>> - TEST("mrs r0, cpsr")
>> - TEST("mrspl r7, cpsr")
>> - TEST("mrs r14, cpsr")
>> + TEST_RMASKED("mrs r",0,~PSR_IGNORE_BITS,", cpsr")
>> + TEST_RMASKED("mrspl r",7,~PSR_IGNORE_BITS,", cpsr")
>> + TEST_RMASKED("mrs r",14,~PSR_IGNORE_BITS,", cpsr")
>> TEST_UNSUPPORTED(__inst_arm(0xe10ff000) " @ mrs r15, cpsr")
>> TEST_UNSUPPORTED("mrs r0, spsr")
>> TEST_UNSUPPORTED("mrs lr, spsr")
>> diff --git a/arch/arm/probes/kprobes/test-core.c b/arch/arm/probes/kprobes/test-core.c
>> index 7c5ddd5..e495127 100644
>> --- a/arch/arm/probes/kprobes/test-core.c
>> +++ b/arch/arm/probes/kprobes/test-core.c
>> @@ -1056,15 +1056,6 @@ static int test_case_run_count;
>> static bool test_case_is_thumb;
>> static int test_instance;
>>
>> -/*
>> - * We ignore the state of the imprecise abort disable flag (CPSR.A) because this
>> - * can change randomly as the kernel doesn't take care to preserve or initialise
>> - * this across context switches. Also, with Security Extentions, the flag may
>> - * not be under control of the kernel; for this reason we ignore the state of
>> - * the FIQ disable flag CPSR.F as well.
>> - */
>> -#define PSR_IGNORE_BITS (PSR_A_BIT | PSR_F_BIT)
>> -
>> static unsigned long test_check_cc(int cc, unsigned long cpsr)
>> {
>> int ret = arm_check_condition(cc << 28, cpsr);
>> @@ -1271,11 +1262,21 @@ test_case_pre_handler(struct kprobe *p, struct pt_regs *regs)
>> static int __kprobes
>> test_after_pre_handler(struct kprobe *p, struct pt_regs *regs)
>> {
>> + struct test_arg *args;
>> +
>> if (container_of(p, struct test_probe, kprobe)->hit == test_instance)
>> return 0; /* Already run for this test instance */
>>
>> result_regs = *regs;
>> +
>> + /* Mask out results which are indeterminate */
>> result_regs.ARM_cpsr &= ~PSR_IGNORE_BITS;
>> + for (args = current_args; args[0].type != ARG_TYPE_END; ++args)
>> + if (args[0].type == ARG_TYPE_REG_MASKED) {
>> + struct test_arg_regptr *arg =
>> + (struct test_arg_regptr *)args;
>> + result_regs.uregs[arg->reg] &= arg->val;
>> + }
>>
>> /* Undo any changes done to SP by the test case */
>> regs->ARM_sp = (unsigned long)current_stack;
>> diff --git a/arch/arm/probes/kprobes/test-core.h b/arch/arm/probes/kprobes/test-core.h
>> index 9991754..32f7aa7 100644
>> --- a/arch/arm/probes/kprobes/test-core.h
>> +++ b/arch/arm/probes/kprobes/test-core.h
>> @@ -45,10 +45,11 @@ extern int kprobe_test_cc_position;
>> *
>> */
>>
>> -#define ARG_TYPE_END 0
>> -#define ARG_TYPE_REG 1
>> -#define ARG_TYPE_PTR 2
>> -#define ARG_TYPE_MEM 3
>> +#define ARG_TYPE_END 0
>> +#define ARG_TYPE_REG 1
>> +#define ARG_TYPE_PTR 2
>> +#define ARG_TYPE_MEM 3
>> +#define ARG_TYPE_REG_MASKED 4
>>
>> #define ARG_FLAG_UNSUPPORTED 0x01
>> #define ARG_FLAG_SUPPORTED 0x02
>> @@ -61,7 +62,7 @@ struct test_arg {
>> };
>>
>> struct test_arg_regptr {
>> - u8 type; /* ARG_TYPE_REG or ARG_TYPE_PTR */
>> + u8 type; /* ARG_TYPE_REG or ARG_TYPE_PTR or ARG_TYPE_REG_MASKED */
>> u8 reg;
>> u8 _padding[2];
>> u32 val;
>> @@ -138,6 +139,12 @@ struct test_arg_end {
>> ".short 0 \n\t" \
>> ".word "#val" \n\t"
>>
>> +#define TEST_ARG_REG_MASKED(reg, val) \
>> + ".byte "__stringify(ARG_TYPE_REG_MASKED)" \n\t" \
>> + ".byte "#reg" \n\t" \
>> + ".short 0 \n\t" \
>> + ".word "#val" \n\t"
>> +
>> #define TEST_ARG_END(flags) \
>> ".byte "__stringify(ARG_TYPE_END)" \n\t" \
>> ".byte "TEST_ISA flags" \n\t" \
>> @@ -395,6 +402,22 @@ struct test_arg_end {
>> " "codex" \n\t" \
>> TESTCASE_END
>>
>> +#define TEST_RMASKED(code1, reg, mask, code2) \
>> + TESTCASE_START(code1 #reg code2) \
>> + TEST_ARG_REG_MASKED(reg, mask) \
>> + TEST_ARG_END("") \
>> + TEST_INSTRUCTION(code1 #reg code2) \
>> + TESTCASE_END
>> +
>> +/*
>> + * We ignore the state of the imprecise abort disable flag (CPSR.A) because this
>> + * can change randomly as the kernel doesn't take care to preserve or initialise
>> + * this across context switches. Also, with Security Extensions, the flag may
>> + * not be under control of the kernel; for this reason we ignore the state of
>> + * the FIQ disable flag CPSR.F as well.
>> + */
>> +#define PSR_IGNORE_BITS (PSR_A_BIT | PSR_F_BIT)
>> +
>>
>> /*
>> * Macros for defining space directives spread over multiple lines.
>> diff --git a/arch/arm/probes/kprobes/test-thumb.c b/arch/arm/probes/kprobes/test-thumb.c
>> index e8cf193..b683b45 100644
>> --- a/arch/arm/probes/kprobes/test-thumb.c
>> +++ b/arch/arm/probes/kprobes/test-thumb.c
>> @@ -778,8 +778,8 @@ CONDITION_INSTRUCTIONS(22,
>>
>> TEST_UNSUPPORTED("subs pc, lr, #4")
>>
>> - TEST("mrs r0, cpsr")
>> - TEST("mrs r14, cpsr")
>> + TEST_RMASKED("mrs r",0,~PSR_IGNORE_BITS,", cpsr")
>> + TEST_RMASKED("mrs r",14,~PSR_IGNORE_BITS,", cpsr")
>> TEST_UNSUPPORTED(__inst_thumb32(0xf3ef8d00) " @ mrs sp, spsr")
>> TEST_UNSUPPORTED(__inst_thumb32(0xf3ef8f00) " @ mrs pc, spsr")
>> TEST_UNSUPPORTED("mrs r0, spsr")
>>
>
> Well, I'm just working on a patch which introducing a TEST_INTOFF and disable interrupts
> for "MRS" testcase. Do you think it is inappropriate? I'll use your patch test for a night
> in my hardware, and will let you know the result tomorrow.
>
> Thank you!
>

Hi Tixy,

I'd like to let you know that I have tested your v3 patch in an ARM cortex A15 board
for 8 hours and nothing bad happened. I'll post a v16 patch series to merge your patch.

Thank you!

>
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