On 04/09/2019 12:47, Dave Martin wrote:
> On Mon, Sep 02, 2019 at 12:29:21pm +0100, Cristian Marussi wrote:
>> Hi
>>
>> this patchset aims to add the initial arch-specific arm64 support to
>> kselftest starting with signals-related test-cases.
>> A common internal test-case layout is proposed which then it is anyway
>> wired-up to the toplevel kselftest Makefile, so that it should be possible
>> at the end to run it on an arm64 target in the usual way with KSFT.
>
> BTW, it's helpful to state the base branch / commit as clearly as
> possible near the top of the cover letter, say,
>
> --8<--
>
> This series is based on arm64/for-next/core [1]
> commit 9ce1263033cd ("selftests, arm64: add a selftest for passing tagged pointers to kernel")
>
> [1] git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/core
>
> -->8--
>
> This is particularly important if you expect the maintainer to pick up
> the patches.
>
> You don't need to reference a specific commit unless there's a
> significant chance of conflicts if the wrong commit is used, but it can
> help provide a clue as to why you're basing on this alternate branch.
>
Ok, thanks I'll do.
>> ~/linux# make TARGETS=arm64 kselftest
>>
>> New KSFT arm64 testcases live inside tools/testing/selftests/arm64 grouped by
>> family inside subdirectories: arm64/signal is the first family proposed with
>> this series.
>> This series converts also to this subdirectory scheme the pre-existing
>> (already queued on arm64/for-next/core) KSFT arm64 tags tests, moving them
>> into arm64/tags.
>>
>> Thanks
>>
>> Cristian
>>
>>
>> Notes:
>> -----
>> - further details in the included READMEs
>>
>> - more tests still to be written (current strategy is going through the related
>> Kernel signal-handling code and write a test for each possible and sensible code-path)
>> A few ideas for more TODO testcases:
>> - fake_sigreturn_unmapped_sp: SP into unmapped addrs
>> - fake_sigreturn_kernelspace_sp: SP into kernel addrs
>> - fake_sigreturn_sve_bad_extra_context: SVE extra context badly formed
>> - mangle_sve_invalid_extra_context: SVE extra_context invalid
>>
>> - SVE signal testcases and special handling will be part of an additional patch
>> still to be released
>
> What's your approach to checking that the test failure paths work?
>
> We could either hack the kernel or the tests to provoke "fake" failures,
> and I don't think it's necessary to test everything in this way,
> providing we have confidence that the test strategy and framework works
> in general.
>
So my approach to testing the tests itself has been as follows:
- PASS path: instrumented Kernel itself to print the exact line where the SEGV
is supposed to be called and manually check once for all (just redone now).
Something like:
# FAKE_SIGRETURN_MISALIGNED_SP :: Triggers a sigreturn with a misaligned sigframe
Registered handlers for all signals.
Detected MINSTKSIGSZ:9984
Testcase initialized.
uc context validated.
GOOD CONTEXT grabbed from sig_copyctx handler
Handled SIG_COPYCTX
Calling sigreturn with fake sigframe sized:4688 at SP @FFFFCAAE5253
[ 188.206911] Kernel SEGV @ 571 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
SIG_OK -- SP:0xFFFFCAAE5253 si_addr@:0xffffcaae5253 si_code:2 token@:0xffffcaae5253 offset:0
==>> completed. PASS(1)
- FAIL path: tried at first the same approach (instrument to avoid the SEGV), but thinking that
this could have led to general Kernel instability while processing bad sigframes,
I instead instrumented tests and utils as follows:
- mangle_ TESTS:
+ removed the "mangling" for each test, and observed test FAIL (NO SEGV)
# MANGLE_PSTATE_INVALID_MODE_EL1h :: Mangling uc_mcontext INVALID MODE EL1h
Registered handlers for all signals.
Detected MINSTKSIGSZ:9984
Testcase initialized.
uc context validated.
Handled SIG_TRIG
==>> completed. FAIL(0)
+ SSBS: being this a peculiar mangle_ test, where we check that SSBS is PRESERVED as it is
on Kernel restoring sigframe (no expected SEGV), I used a kernel patched to NOT preserve
the SSBS bit (so clearing it). Moreover I experimented with the various SSBS support levels
(no_supp/SSBS_BIT/MRS+SSBS_BIT) and observed how test behaved related to the detected SSBS support
+ verify that an anomalous SEGV (no SEGV_ACCER) is detected (say a *(* int)0x00= inside handler)
# MANGLE_PSTATE_INVALID_DAIF_BITS :: Mangling uc_mcontext with INVALID DAIF_BITS
Registered handlers for all signals.
Detected MINSTKSIGSZ:9984
Testcase initialized.
uc context validated.
SIG_OK -- SP:0xFFFFFBE96DA0 si_addr@:(nil) si_code:1 token@:(nil) offset:0
si_code != SEGV_ACCERR...test is probably broken! <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
-- RX UNEXPECTED SIGNAL: 6
==>> completed. FAIL(0)
- fake_sigreturn_ TESTS:
+ verify placing on the stack the good context grabbed from get_current_context() as it is
(GOOD), execution flow is anomalously restored inside get_current_context() and such
anomaly is spotted (without deadly loops)
# FAKE_SIGRETURN_BAD_MAGIC :: Trigger a sigreturn with a sigframe with a bad magic
Registered handlers for all signals.
Detected MINSTKSIGSZ:9984
Testcase initialized.
uc context validated.
GOOD CONTEXT grabbed from sig_copyctx handler
Handled SIG_COPYCTX
Calling sigreturn with fake sigframe sized:4688 at SP @FFFFCAC61F80
Unexpected successful sigreturn detected: live_uc is stale ! <<<<<<<<<<<<<<<<<<<<<<<<<<<
==>> completed. FAIL(0)
+ verify that an early SEGV is detected as anomalous (say a *(* int)0x00 before fake sigframe
has been placed on the stack)
# FAKE_SIGRETURN_BAD_MAGIC :: Trigger a sigreturn with a sigframe with a bad magic
Registered handlers for all signals.
Detected MINSTKSIGSZ:9984
Testcase initialized.
uc context validated.
GOOD CONTEXT grabbed from sig_copyctx handler
Handled SIG_COPYCTX
Available space:3552
Using badly built context - ERR: BAD MAGIC !
Calling sigreturn with fake sigframe sized:4688 at SP @FFFFE77C96D0
SIG_OK -- SP:0xFFFFE77C96D0 si_addr@:(nil) si_code:1 token@:(nil) offset:0
current->token ZEROED...test is probably broken! <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
-- RX UNEXPECTED SIGNAL: 6
==>> completed. FAIL(0)
> [...]
>
> Cheers
> ---Dave
>
Cheers
Cristian
