Subject: Re: [PATCH v5 09/11] kselftest: arm64: fake_sigreturn_duplicated_fpsimd

From: Cristian Marussi <[email-masked]>
Date: Thu, 5 Sep 2019 14:32:09 +0100

On 05/09/2019 13:39, Dave Martin wrote:
> On Thu, Sep 05, 2019 at 01:15:58PM +0100, Cristian Marussi wrote:
>> Hi
>>
>> On 04/09/2019 12:49, Dave Martin wrote:
>>> On Mon, Sep 02, 2019 at 12:29:30pm +0100, Cristian Marussi wrote:
>>>> Add a simple fake_sigreturn testcase which builds a ucontext_t with
>>>> an anomalous additional fpsimd_context and place it onto the stack.
>>>> Expects a SIGSEGV on test PASS.
>>>>
>>>> Signed-off-by: Cristian Marussi <[email-masked]>
>>>> ---
>>>> v3 --> v4
>>>> - fix commit
>>>> - missing include
>>>> - using new get_starting_head() helper
>>>> - added test description
>>>> ---
>>>>  .../fake_sigreturn_duplicated_fpsimd.c        | 52 +++++++++++++++++++
>>>>  1 file changed, 52 insertions(+)
>>>>  create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_duplicated_fpsimd.c
>>>>
>>>> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_duplicated_fpsimd.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_duplicated_fpsimd.c
>>>> new file mode 100644
>>>> index 000000000000..c7122c44f53f
>>>> --- /dev/null
>>>> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_duplicated_fpsimd.c
>>>> @@ -0,0 +1,52 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Copyright (C) 2019 ARM Limited
>>>> + *
>>>> + * Place a fake sigframe on the stack including an additional FPSIMD
>>>> + * record: on sigreturn Kernel must spot this attempt and the test
>>>> + * case is expected to be terminated via SEGV.
>>>> + */
>>>> +
>>>> +#include <signal.h>
>>>> +#include <ucontext.h>
>>>> +
>>>> +#include "test_signals_utils.h"
>>>> +#include "testcases.h"
>>>> +
>>>> +struct fake_sigframe sf;
>>>> +
>>>> +static int fake_sigreturn_duplicated_fpsimd_run(struct tdescr *td,
>>>> +						siginfo_t *si, ucontext_t *uc)
>>>> +{
>>>> +	size_t resv_sz, need_sz;
>>>> +	struct _aarch64_ctx *shead = GET_SF_RESV_HEAD(sf), *head;
>>>> +
>>>> +	/* just to fill the ucontext_t with something real */
>>>> +	if (!get_current_context(td, &sf.uc))
>>>> +		return 1;
>>>> +
>>>> +	resv_sz = GET_SF_RESV_SIZE(sf);
>>>> +	need_sz = HDR_SZ + sizeof(struct fpsimd_context);
>>>
>>> Nit: Maybe write this sum in the same order as the records we're going 
>>> o append, i.e.:
>>>
>>> 	need_sz = sizeof(struct fpsimd_context) + HDR_SZ; /* for terminator */
>>
>> Ok
>>
>>>
>>> Also, maybe fail this test if there is no fpsimd_context in the initial
>>> frame from get_current_context(): that would be a kernel bug, but we
>>> wouldn't be giving fake_sigreturn() duplicate fpsimd_contexts in that
>>> case -- so this test wouldn't test the thing it's supposed to test.
>>>
>>
>> Any context grabbed by get_current_context() is verified at first to be sane
>> when is copied in the handler by ASSERT_GOOD_CONTEXT()
>>
>>>   } else if (signum == sig_copyctx && current->live_uc) {
>>>                 memcpy(current->live_uc, uc, current->live_sz);
>>>                 ASSERT_GOOD_CONTEXT(current->live_uc);
>>>                 current->live_uc_valid = 1;
>>
>> A missing fpsimd in the original sigframe would lead to an abort()
>> straight away while preparing the test, and the test will fail.
> 
> OK, but there is no abort() in ASSERT_GOOD_CONTEXT(), only assert(0).
> Can you add an abort() after the assert() in there in patch 2?
> 
Ok yes, I meant the abort coming from assert(0) in fact....I'll review all
the critical asserts for additional aborts in V6

> People probably aren't going to be building the tests with -DNDEBUG, but
> we should avoid unnecessary surprises...
> 
> Cheers
> ---Dave
> 

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