Subject: Re: [PATCH v3 11/11] kselftest: arm64: fake_sigreturn_misaligned_sp

From: Cristian Marussi <[email-masked]>
Date: Fri, 30 Aug 2019 17:33:25 +0100

On 13/08/2019 17:27, Dave Martin wrote:
> On Fri, Aug 02, 2019 at 06:03:00PM +0100, Cristian Marussi wrote:
>> Added a simple fake_sigreturn testcase which places a valid
> 
> Add
> 
Ok

>> sigframe on a non-16 bytes aligned SP.
>> fake_sigretrun() helper function has been patched accordingly
>> to support placing a sigframe on a non-16 bytes aligned address.
>> Expects a SIGSEGV on test PASS.
>>
>> Adds also a test TODO lists holding some further test ideas.
> 
> Adds -> Also add
> lists -> list
> 

Removed together with the TODO.

>> Signed-off-by: Cristian Marussi <[email-masked]>
>> ---
>> Re-added this text after fixing the forced misaglinment procedure in
>> fake_sigreturn() itself: require a ZERO alignment and you'll get
>> your sigframe placed on a misaligned SP (2-bytes off the 16-align)
>> ---
>>  .../testing/selftests/arm64/signal/signals.S  | 21 +++++++++----
>>  .../arm64/signal/testcases/TODO.readme        |  8 +++++
>>  .../testcases/fake_sigreturn_misaligned_sp.c  | 30 +++++++++++++++++++
>>  3 files changed, 53 insertions(+), 6 deletions(-)
>>  create mode 100644 tools/testing/selftests/arm64/signal/testcases/TODO.readme
>>  create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
>>
>> diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S
>> index 6262b877400b..2099871176ed 100644
>> --- a/tools/testing/selftests/arm64/signal/signals.S
>> +++ b/tools/testing/selftests/arm64/signal/signals.S
>> @@ -13,19 +13,28 @@ call_fmt:
>>  
>>  .globl fake_sigreturn
>>  
>> -/*	fake_sigreturn	x0:&sigframe,  x1:sigframe_size,  x2:alignment_SP */
>> +/*	fake_sigreturn	x0:&sigframe, x1:sigframe_sz, x2:align */
>>  fake_sigreturn:
>> -	mov x20, x0
>> -	mov x21, x1
>> -	mov x22, x2
>> -	mov x23, sp
>>  
>> -	/* create space on the stack for fake sigframe..."x22"-aligned */
>> +	/* Save args and decide which aligment to enforce */
>> +	mov 	x23, sp
>> +	mov	x20, x0
>> +	mov 	x21, x1
>> +	/* x22 and x24 used for forcing alignment or misalignment */
>> +	mov	x22, x2
>> +	mov	x24, #0
>> +	cbnz	x22, 1f
>> +	mov	x22, #16
>> +	mov	x24, #2
>> +
>> +1:	/* create space on the stack for fake sigframe..."x22"-aligned */
>>  	mov x0, #0
>>  	add x0, x21, x22
>>  	sub x22, x22, #1
>>  	bic x0, x0, x22
>>  	sub x23, x23, x0
>> +	/* force misaligned by x24 bytes if required alignment was zero */
>> +	add x23, x23, x24
>>  
>>  	ldr x0, =call_fmt
>>  	mov x1, x21
> 
> Would it be simpler for the third argument to specify a number of bytes
> to subtract from SP after allocating 16-byte aligned storage to
> accommodate sigframe_sz?
> 
> Then 0 gives an aligned frame, 1 gives a frame misaligned by 1 byte,
> etc.
> 
> 
> Also if all this is a fix to the original fake_sigreturn, can we merge
> it into the original patch instead?
> 
Yes simplified and merged into 6/11

>> diff --git a/tools/testing/selftests/arm64/signal/testcases/TODO.readme b/tools/testing/selftests/arm64/signal/testcases/TODO.readme
>> new file mode 100644
>> index 000000000000..5c949492e7ab
>> --- /dev/null
>> +++ b/tools/testing/selftests/arm64/signal/testcases/TODO.readme
>> @@ -0,0 +1,8 @@
>> +Some more possible ideas for signals tests:
>> +
>> +- fake_sigreturn_unmapped_sp
>> +- fake_sigreturn_kernelspace_sp
>> +- fake_sigreturn_sve_bad_extra_context
>> +- mangle_sve_invalid_extra_context
>> +- mangle_pstate_invalid_el for H modes (+ macroization ?)
>> +- fake_sigreturn_overflow_reserved
> 
> This seems a reasonable list, but it occurs to me that it will tend to
> go out of sync as tests get added.  So maybe just put this list in the
> cover letter instead of including it in the patch.
> 
> We should probably have a one-line description of each proposed test,
> since the names are a bit cryptic.

Moving to cover letter with description.

> 
>> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
>> new file mode 100644
>> index 000000000000..3ee8c500c7d1
>> --- /dev/null
>> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
>> @@ -0,0 +1,30 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/* Copyright (C) 2019 ARM Limited */
>> +
> 
> signal.h?

ok
> 
>> +#include <ucontext.h>
>> +
>> +#include "test_signals_utils.h"
>> +#include "testcases.h"
>> +
>> +struct fake_sigframe sf;
>> +
>> +static int fake_sigreturn_misaligned_run(struct tdescr *td,
>> +				         siginfo_t *si, ucontext_t *uc)
>> +{
>> +	/* just to fill the ucontext_t with something real */
>> +	if (!get_current_context(td, &sf.uc))
>> +		return 1;
>> +
>> +	/* Forcing sigframe on misaligned (=!16) SP */
>> +	fake_sigreturn(&sf, sizeof(sf), 0);
>> +
>> +	return 1;
>> +}
> 
> [...]
> 
> Cheers
> ---Dave
> 

Cheers

Cristian

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