[v3,06/11] kselftest: arm64: fake_sigreturn_bad_magic
diff mbox series

Message ID 20190802170300.20662-7-cristian.marussi@arm.com
State New
Headers show
Series
  • Add arm64/signal initial kselftest support
Related show

Commit Message

Cristian Marussi Aug. 2, 2019, 5:02 p.m. UTC
Added a simple fake_sigreturn testcase which builds a ucontext_t
with a bad magic header and place it onto the stack.
Expects a SIGSEGV on test PASS.
This commit also introduces a common utility assembly function to
invoke a sigreturn using a fake provided sigframe.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
 tools/testing/selftests/arm64/signal/Makefile |  2 +-
 .../testing/selftests/arm64/signal/signals.S  | 64 +++++++++++++++++++
 .../arm64/signal/test_signals_utils.h         |  1 +
 .../arm64/signal/testcases/.gitignore         |  1 +
 .../testcases/fake_sigreturn_bad_magic.c      | 63 ++++++++++++++++++
 5 files changed, 130 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/arm64/signal/signals.S
 create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c

Comments

Dave Martin Aug. 13, 2019, 4:25 p.m. UTC | #1
On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:
> Added a simple fake_sigreturn testcase which builds a ucontext_t

Add

> with a bad magic header and place it onto the stack.
> Expects a SIGSEGV on test PASS.
> This commit also introduces a common utility assembly function to
> invoke a sigreturn using a fake provided sigframe.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---
>  tools/testing/selftests/arm64/signal/Makefile |  2 +-
>  .../testing/selftests/arm64/signal/signals.S  | 64 +++++++++++++++++++
>  .../arm64/signal/test_signals_utils.h         |  1 +
>  .../arm64/signal/testcases/.gitignore         |  1 +
>  .../testcases/fake_sigreturn_bad_magic.c      | 63 ++++++++++++++++++
>  5 files changed, 130 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/arm64/signal/signals.S
>  create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
> 
> diff --git a/tools/testing/selftests/arm64/signal/Makefile b/tools/testing/selftests/arm64/signal/Makefile
> index 8c8d08be4b0d..b3dcf315b5a4 100644
> --- a/tools/testing/selftests/arm64/signal/Makefile
> +++ b/tools/testing/selftests/arm64/signal/Makefile
> @@ -80,7 +80,7 @@ endif
>  # Common test-unit targets to build common-layout test-cases executables
>  # Needs secondary expansion to properly include the testcase c-file in pre-reqs
>  .SECONDEXPANSION:
> -$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
> +$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c signals.S $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
>  	@if [ ! -d $(khdr_dir) ]; then \
>  		echo -n "\n!!! WARNING: $(khdr_dir) NOT FOUND."; \
>  		echo "===>  Are you sure Kernel Headers have been installed properly ?\n"; \
> diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S
> new file mode 100644
> index 000000000000..6262b877400b
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/signal/signals.S
> @@ -0,0 +1,64 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0
> + * Copyright (C) 2019 ARM Limited
> + */
> +
> +#include <asm/unistd.h>
> +
> +.section        ".rodata", "a"

The section name is not usually quoted in .section (though I guess it
works).

> +call_fmt:
> +	.asciz "Calling sigreturn with fake sigframe sized:%zd at calculated SP @%08lX\n"
> +
> +.text
> +
> +.globl fake_sigreturn
> +
> +/*	fake_sigreturn	x0:&sigframe,  x1:sigframe_size,  x2:alignment_SP */
> +fake_sigreturn:
> +	mov x20, x0
> +	mov x21, x1
> +	mov x22, x2
> +	mov x23, sp
> +
> +	/* create space on the stack for fake sigframe..."x22"-aligned */
> +	mov x0, #0

Why to we move 0 into x0?  We clobber x0 again in the next instruction:

> +	add x0, x21, x22
> +	sub x22, x22, #1
> +	bic x0, x0, x22
> +	sub x23, x23, x0

Can you explain the logic here?  I'm not sure I understand what this is
trying to do exactly.

I notice you further modify this in patch 11 -- see my comments there,
where I also suggest an alternative way of specifying a misaligned frame
that might be simpler.

> +
> +	ldr x0, =call_fmt
> +	mov x1, x21
> +	mov x2, x23
> +	bl printf
> +
> +	mov sp, x23
> +
> +	/* now fill it with the provided content... */
> +	mov x0, sp
> +	mov x1, x20
> +	mov x2, x21
> +	bl memcpy
> +
> +	/*
> +	 * Here saving a last minute SP to current->token acts as a marker:
> +	 * if we got here, we are successfully faking a sigreturn; in other
> +	 * words we are sure no bad fatal signal has been raised till now
> +	 * for unrelated reasons, so we should consider the possibl observed

typo: possible (or possibly?)

> +	 * fatal signal like SEGV coming from Kernel restore_sigframe() and
> +	 * triggered as expected from our test-case.
> +	 * For simplicity this assumes that current field 'token' is laid out
> +	 * as first in struct tdescr
> +	 */
> +	ldr x0, current
> +	str x23, [x0]
> +	/* SP is already pointing back to the just built fake sigframe here */
> +	mov x8, #__NR_rt_sigreturn
> +	svc #0
> +
> +	/*
> +	 * Above sigreturn should not return...looping here leads to a timeout
> +	 * and ensure proper and clean test failure, instead of jumping around
> +	 * on a potentially corrupted stack.
> +	 */
> +	b .
> diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h
> index ce35be8ebc8e..2a71da7e6695 100644
> --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h
> +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h
> @@ -12,4 +12,5 @@ int test_run(struct tdescr *td);
>  void test_result(struct tdescr *td);
>  
>  bool get_current_context(struct tdescr *td, ucontext_t *dest_uc);
> +int fake_sigreturn(void *sigframe, size_t sz, int alignment);
>  #endif
> diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore
> index a48a118b1a1a..0ea6fdc3765c 100644
> --- a/tools/testing/selftests/arm64/signal/testcases/.gitignore
> +++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore
> @@ -4,3 +4,4 @@ mangle_pstate_invalid_mode_el1
>  mangle_pstate_invalid_mode_el2
>  mangle_pstate_invalid_mode_el3
>  mangle_pstate_ssbs_regs
> +fake_sigreturn_bad_magic
> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
> new file mode 100644
> index 000000000000..b4c063e02a7a
> --- /dev/null
> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2019 ARM Limited */
> +

We should probably also include <signal.h> here, since we're using
siginfo_t etc.

> +#include <stdio.h>
> +#include <ucontext.h>
> +
> +#include "test_signals_utils.h"
> +#include "testcases.h"
> +
> +struct fake_sigframe sf;
> +
> +static int fake_sigreturn_bad_magic_run(struct tdescr *td,
> +					siginfo_t *si, ucontext_t *uc)
> +{
> +	size_t resv_sz, offset;
> +	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);
> +	/*
> +	 * find the terminator, preserving existing headers
> +	 * and verify amount of spare room in __reserved area.
> +	 */
> +	head = get_terminator(shead, resv_sz, &offset);
> +	/*
> +	 * try stripping extra_context header when low on space:
> +	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
> +	 * and the other for the usual terminator.
> +	 */
> +	if (head && resv_sz - offset < HDR_SZ * 2) {

Can we factor out this logic for finding space in the signal frame?

We do pretty much the same thing in all the fake_sigreturn tests...

> +		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
> +			resv_sz - offset);
> +		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
> +	}
> +	/* just give up and timeout if still not enough space */

Do we actually time out?  I don't see where we actually wait, so doesn't
test_run() just fail immediately?

The same applies to all the other fake_sigreturn tests too.

> +	if (head && resv_sz - offset >= HDR_SZ) {

Should this be HDR_SZ * 2 again?  We need space for the face header and
space to write a terminator after it.

> +		fprintf(stderr, "Mangling template header. Spare space:%zd\n",
> +			resv_sz - offset);
> +		/*
> +		 * use a well known NON existent bad magic...something
> +		 * we should pretty sure won't be ever defined in Kernel
> +		 */
> +		head->magic = KSFT_BAD_MAGIC;
> +		head->size = HDR_SZ;
> +		write_terminator_record(GET_RESV_NEXT_HEAD(head));
> +
> +		ASSERT_BAD_CONTEXT(&sf.uc);
> +		fake_sigreturn(&sf, sizeof(sf), 16);
> +	}
> +
> +	return 1;
> +}

[...]

Cheers
---Dave
Cristian Marussi Aug. 30, 2019, 2:29 p.m. UTC | #2
Hi

On 13/08/2019 17:25, Dave Martin wrote:
> On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:
>> Added a simple fake_sigreturn testcase which builds a ucontext_t
> 
> Add

Ok
> 
>> with a bad magic header and place it onto the stack.
>> Expects a SIGSEGV on test PASS.
>> This commit also introduces a common utility assembly function to
>> invoke a sigreturn using a fake provided sigframe.
>>
>> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
>> ---
>>  tools/testing/selftests/arm64/signal/Makefile |  2 +-
>>  .../testing/selftests/arm64/signal/signals.S  | 64 +++++++++++++++++++
>>  .../arm64/signal/test_signals_utils.h         |  1 +
>>  .../arm64/signal/testcases/.gitignore         |  1 +
>>  .../testcases/fake_sigreturn_bad_magic.c      | 63 ++++++++++++++++++
>>  5 files changed, 130 insertions(+), 1 deletion(-)
>>  create mode 100644 tools/testing/selftests/arm64/signal/signals.S
>>  create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
>>
>> diff --git a/tools/testing/selftests/arm64/signal/Makefile b/tools/testing/selftests/arm64/signal/Makefile
>> index 8c8d08be4b0d..b3dcf315b5a4 100644
>> --- a/tools/testing/selftests/arm64/signal/Makefile
>> +++ b/tools/testing/selftests/arm64/signal/Makefile
>> @@ -80,7 +80,7 @@ endif
>>  # Common test-unit targets to build common-layout test-cases executables
>>  # Needs secondary expansion to properly include the testcase c-file in pre-reqs
>>  .SECONDEXPANSION:
>> -$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
>> +$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c signals.S $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
>>  	@if [ ! -d $(khdr_dir) ]; then \
>>  		echo -n "\n!!! WARNING: $(khdr_dir) NOT FOUND."; \
>>  		echo "===>  Are you sure Kernel Headers have been installed properly ?\n"; \
>> diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S
>> new file mode 100644
>> index 000000000000..6262b877400b
>> --- /dev/null
>> +++ b/tools/testing/selftests/arm64/signal/signals.S
>> @@ -0,0 +1,64 @@
>> +/*
>> + * SPDX-License-Identifier: GPL-2.0
>> + * Copyright (C) 2019 ARM Limited
>> + */
>> +
>> +#include <asm/unistd.h>
>> +
>> +.section        ".rodata", "a"
> 
> The section name is not usually quoted in .section (though I guess it
> works).
> 
Ok

>> +call_fmt:
>> +	.asciz "Calling sigreturn with fake sigframe sized:%zd at calculated SP @%08lX\n"
>> +
>> +.text
>> +
>> +.globl fake_sigreturn
>> +
>> +/*	fake_sigreturn	x0:&sigframe,  x1:sigframe_size,  x2:alignment_SP */
>> +fake_sigreturn:
>> +	mov x20, x0
>> +	mov x21, x1
>> +	mov x22, x2
>> +	mov x23, sp
>> +
>> +	/* create space on the stack for fake sigframe..."x22"-aligned */
>> +	mov x0, #0
> 
> Why to we move 0 into x0?  We clobber x0 again in the next instruction:
Yes unneeded.

>> +	add x0, x21, x22
>> +	sub x22, x22, #1
>> +	bic x0, x0, x22
>> +	sub x23, x23, x0
> 
> Can you explain the logic here?  I'm not sure I understand what this is
> trying to do exactly.

The attempt is to make space on the stack for a x22-bytes-aligned sigframe
of at least x21-bytes-size (assuming x22 is power-of-two):

- calculate the needed aligned space (sigframe_size + x22) & ~(x22 - 1)
- calculate new SP in x23: x3 = sp - needed_aligned_space
- later down... move SP to the calculated sp in x23
- copy the provided sigframe on such new SP

> I notice you further modify this in patch 11 -- see my comments there,
> where I also suggest an alternative way of specifying a misaligned frame
> that might be simpler.

I've seen your comments on patch 11. I think I'll simplify that as you suggested:
patch 11 was meant to add the capability to misalign the sigframe  on the SP
(which is needed in testcase contained in 11) but in fact is better if I move all
of the simplified logic here.

>> +
>> +	ldr x0, =call_fmt
>> +	mov x1, x21
>> +	mov x2, x23
>> +	bl printf
>> +
>> +	mov sp, x23
>> +
>> +	/* now fill it with the provided content... */
>> +	mov x0, sp
>> +	mov x1, x20
>> +	mov x2, x21
>> +	bl memcpy
>> +
>> +	/*
>> +	 * Here saving a last minute SP to current->token acts as a marker:
>> +	 * if we got here, we are successfully faking a sigreturn; in other
>> +	 * words we are sure no bad fatal signal has been raised till now
>> +	 * for unrelated reasons, so we should consider the possibl observed
> 
> typo: possible (or possibly?)
> 
possibly

>> +	 * fatal signal like SEGV coming from Kernel restore_sigframe() and
>> +	 * triggered as expected from our test-case.
>> +	 * For simplicity this assumes that current field 'token' is laid out
>> +	 * as first in struct tdescr
>> +	 */
>> +	ldr x0, current
>> +	str x23, [x0]
>> +	/* SP is already pointing back to the just built fake sigframe here */
>> +	mov x8, #__NR_rt_sigreturn
>> +	svc #0
>> +
>> +	/*
>> +	 * Above sigreturn should not return...looping here leads to a timeout
>> +	 * and ensure proper and clean test failure, instead of jumping around
>> +	 * on a potentially corrupted stack.
>> +	 */
>> +	b .
>> diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h
>> index ce35be8ebc8e..2a71da7e6695 100644
>> --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h
>> +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h
>> @@ -12,4 +12,5 @@ int test_run(struct tdescr *td);
>>  void test_result(struct tdescr *td);
>>  
>>  bool get_current_context(struct tdescr *td, ucontext_t *dest_uc);
>> +int fake_sigreturn(void *sigframe, size_t sz, int alignment);
>>  #endif
>> diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore
>> index a48a118b1a1a..0ea6fdc3765c 100644
>> --- a/tools/testing/selftests/arm64/signal/testcases/.gitignore
>> +++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore
>> @@ -4,3 +4,4 @@ mangle_pstate_invalid_mode_el1
>>  mangle_pstate_invalid_mode_el2
>>  mangle_pstate_invalid_mode_el3
>>  mangle_pstate_ssbs_regs
>> +fake_sigreturn_bad_magic
>> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
>> new file mode 100644
>> index 000000000000..b4c063e02a7a
>> --- /dev/null
>> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
>> @@ -0,0 +1,63 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/* Copyright (C) 2019 ARM Limited */
>> +
> 
> We should probably also include <signal.h> here, since we're using
> siginfo_t etc.

Yes indeed. It was included via some other headers only.
> 
>> +#include <stdio.h>
>> +#include <ucontext.h>
>> +
>> +#include "test_signals_utils.h"
>> +#include "testcases.h"
>> +
>> +struct fake_sigframe sf;
>> +
>> +static int fake_sigreturn_bad_magic_run(struct tdescr *td,
>> +					siginfo_t *si, ucontext_t *uc)
>> +{
>> +	size_t resv_sz, offset;
>> +	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);
>> +	/*
>> +	 * find the terminator, preserving existing headers
>> +	 * and verify amount of spare room in __reserved area.
>> +	 */
>> +	head = get_terminator(shead, resv_sz, &offset);
>> +	/*
>> +	 * try stripping extra_context header when low on space:
>> +	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
>> +	 * and the other for the usual terminator.
>> +	 */
>> +	if (head && resv_sz - offset < HDR_SZ * 2) {
> 
> Can we factor out this logic for finding space in the signal frame?
> 
> We do pretty much the same thing in all the fake_sigreturn tests...

Ok
> 
>> +		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
>> +			resv_sz - offset);
>> +		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
>> +	}
>> +	/* just give up and timeout if still not enough space */
> 
> Do we actually time out?  I don't see where we actually wait, so doesn't
> test_run() just fail immediately?
> 
> The same applies to all the other fake_sigreturn tests too.
> 
Right. It is probably a leftover.

SIGALRM is used as an extreme measure to kill tests gone bad, but this
can happen only once the fake sigframe has been effectively placed on the stack
and sigreturned.


>> +	if (head && resv_sz - offset >= HDR_SZ) {
> 
> Should this be HDR_SZ * 2 again?  We need space for the face header and
> space to write a terminator after it.

I'll fix in the new factored out code.

> 
>> +		fprintf(stderr, "Mangling template header. Spare space:%zd\n",
>> +			resv_sz - offset);
>> +		/*
>> +		 * use a well known NON existent bad magic...something
>> +		 * we should pretty sure won't be ever defined in Kernel
>> +		 */
>> +		head->magic = KSFT_BAD_MAGIC;
>> +		head->size = HDR_SZ;
>> +		write_terminator_record(GET_RESV_NEXT_HEAD(head));
>> +
>> +		ASSERT_BAD_CONTEXT(&sf.uc);
>> +		fake_sigreturn(&sf, sizeof(sf), 16);
>> +	}
>> +
>> +	return 1;
>> +}
> 
> [...]
> 
> Cheers
> ---Dave
> 

Cheers

Cristian
Dave Martin Sept. 4, 2019, 10:05 a.m. UTC | #3
On Fri, Aug 30, 2019 at 03:29:29PM +0100, Cristian Marussi wrote:
> Hi
> 
> On 13/08/2019 17:25, Dave Martin wrote:
> > On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:

[...]

> >> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c

[...]

> >> +static int fake_sigreturn_bad_magic_run(struct tdescr *td,
> >> +					siginfo_t *si, ucontext_t *uc)
> >> +{
> >> +	size_t resv_sz, offset;
> >> +	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);
> >> +	/*
> >> +	 * find the terminator, preserving existing headers
> >> +	 * and verify amount of spare room in __reserved area.
> >> +	 */
> >> +	head = get_terminator(shead, resv_sz, &offset);
> >> +	/*
> >> +	 * try stripping extra_context header when low on space:
> >> +	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
> >> +	 * and the other for the usual terminator.
> >> +	 */
> >> +	if (head && resv_sz - offset < HDR_SZ * 2) {
> > 
> > Can we factor out this logic for finding space in the signal frame?
> > 
> > We do pretty much the same thing in all the fake_sigreturn tests...
> 
> Ok
> > 
> >> +		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
> >> +			resv_sz - offset);
> >> +		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
> >> +	}
> >> +	/* just give up and timeout if still not enough space */
> > 
> > Do we actually time out?  I don't see where we actually wait, so doesn't
> > test_run() just fail immediately?
> > 
> > The same applies to all the other fake_sigreturn tests too.
> > 
> Right. It is probably a leftover.
> 
> SIGALRM is used as an extreme measure to kill tests gone bad, but this
> can happen only once the fake sigframe has been effectively placed on the stack
> and sigreturned.

OK, so this gets reported as a test failure because with no SIGSEGV,
nothing ever sets td->pass?

This is probably OK for now, though I wonder whether this should be
reported as a skipped test instead.

In case of doubt, reporting a failure is preferable anyway, since that
will encourage people actually to investigate what went wrong.

[...]

Cheers
---Dave
Cristian Marussi Sept. 4, 2019, 10:37 a.m. UTC | #4
On 04/09/2019 11:05, Dave Martin wrote:
> On Fri, Aug 30, 2019 at 03:29:29PM +0100, Cristian Marussi wrote:
>> Hi
>>
>> On 13/08/2019 17:25, Dave Martin wrote:
>>> On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:
> 
> [...]
> 
>>>> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
> 
> [...]
> 
>>>> +static int fake_sigreturn_bad_magic_run(struct tdescr *td,
>>>> +					siginfo_t *si, ucontext_t *uc)
>>>> +{
>>>> +	size_t resv_sz, offset;
>>>> +	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);
>>>> +	/*
>>>> +	 * find the terminator, preserving existing headers
>>>> +	 * and verify amount of spare room in __reserved area.
>>>> +	 */
>>>> +	head = get_terminator(shead, resv_sz, &offset);
>>>> +	/*
>>>> +	 * try stripping extra_context header when low on space:
>>>> +	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
>>>> +	 * and the other for the usual terminator.
>>>> +	 */
>>>> +	if (head && resv_sz - offset < HDR_SZ * 2) {
>>>
>>> Can we factor out this logic for finding space in the signal frame?
>>>
>>> We do pretty much the same thing in all the fake_sigreturn tests...
>>
>> Ok
>>>
>>>> +		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
>>>> +			resv_sz - offset);
>>>> +		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
>>>> +	}
>>>> +	/* just give up and timeout if still not enough space */
>>>
>>> Do we actually time out?  I don't see where we actually wait, so doesn't
>>> test_run() just fail immediately?
>>>
>>> The same applies to all the other fake_sigreturn tests too.
>>>
>> Right. It is probably a leftover.
>>
>> SIGALRM is used as an extreme measure to kill tests gone bad, but this
>> can happen only once the fake sigframe has been effectively placed on the stack
>> and sigreturned.
> 
> OK, so this gets reported as a test failure because with no SIGSEGV,
> nothing ever sets td->pass?

Yes exactly. End result is based on value on td->pass, in case of abrupt
termination or timeout nobody sets td->pass ever.
> 
> This is probably OK for now, though I wonder whether this should be
> reported as a skipped test instead.
> 
> In case of doubt, reporting a failure is preferable anyway, since that
> will encourage people actually to investigate what went wrong.
> 

As of now I never skip a test in fact...also tests for unsupported features
are built and run expecting a SIGILL, and reported as PASS in that case.

Cristian
> [...]
> 
> Cheers
> ---Dave
>
Dave Martin Sept. 4, 2019, 10:47 a.m. UTC | #5
On Wed, Sep 04, 2019 at 11:37:36AM +0100, Cristian Marussi wrote:
> On 04/09/2019 11:05, Dave Martin wrote:
> > On Fri, Aug 30, 2019 at 03:29:29PM +0100, Cristian Marussi wrote:
> >> Hi
> >>
> >> On 13/08/2019 17:25, Dave Martin wrote:
> >>> On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote:
> > 
> > [...]
> > 
> >>>> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
> > 
> > [...]
> > 
> >>>> +static int fake_sigreturn_bad_magic_run(struct tdescr *td,
> >>>> +					siginfo_t *si, ucontext_t *uc)
> >>>> +{
> >>>> +	size_t resv_sz, offset;
> >>>> +	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);
> >>>> +	/*
> >>>> +	 * find the terminator, preserving existing headers
> >>>> +	 * and verify amount of spare room in __reserved area.
> >>>> +	 */
> >>>> +	head = get_terminator(shead, resv_sz, &offset);
> >>>> +	/*
> >>>> +	 * try stripping extra_context header when low on space:
> >>>> +	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
> >>>> +	 * and the other for the usual terminator.
> >>>> +	 */
> >>>> +	if (head && resv_sz - offset < HDR_SZ * 2) {
> >>>
> >>> Can we factor out this logic for finding space in the signal frame?
> >>>
> >>> We do pretty much the same thing in all the fake_sigreturn tests...
> >>
> >> Ok
> >>>
> >>>> +		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
> >>>> +			resv_sz - offset);
> >>>> +		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
> >>>> +	}
> >>>> +	/* just give up and timeout if still not enough space */
> >>>
> >>> Do we actually time out?  I don't see where we actually wait, so doesn't
> >>> test_run() just fail immediately?
> >>>
> >>> The same applies to all the other fake_sigreturn tests too.
> >>>
> >> Right. It is probably a leftover.
> >>
> >> SIGALRM is used as an extreme measure to kill tests gone bad, but this
> >> can happen only once the fake sigframe has been effectively placed on the stack
> >> and sigreturned.
> > 
> > OK, so this gets reported as a test failure because with no SIGSEGV,
> > nothing ever sets td->pass?
> 
> Yes exactly. End result is based on value on td->pass, in case of abrupt
> termination or timeout nobody sets td->pass ever.
> > 
> > This is probably OK for now, though I wonder whether this should be
> > reported as a skipped test instead.
> > 
> > In case of doubt, reporting a failure is preferable anyway, since that
> > will encourage people actually to investigate what went wrong.
> > 
> 
> As of now I never skip a test in fact...also tests for unsupported features
> are built and run expecting a SIGILL, and reported as PASS in that case.

OK, just wanted to check I'd understood correcly.

Cheers
---Dave

Patch
diff mbox series

diff --git a/tools/testing/selftests/arm64/signal/Makefile b/tools/testing/selftests/arm64/signal/Makefile
index 8c8d08be4b0d..b3dcf315b5a4 100644
--- a/tools/testing/selftests/arm64/signal/Makefile
+++ b/tools/testing/selftests/arm64/signal/Makefile
@@ -80,7 +80,7 @@  endif
 # Common test-unit targets to build common-layout test-cases executables
 # Needs secondary expansion to properly include the testcase c-file in pre-reqs
 .SECONDEXPANSION:
-$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
+$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c signals.S $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
 	@if [ ! -d $(khdr_dir) ]; then \
 		echo -n "\n!!! WARNING: $(khdr_dir) NOT FOUND."; \
 		echo "===>  Are you sure Kernel Headers have been installed properly ?\n"; \
diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S
new file mode 100644
index 000000000000..6262b877400b
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/signals.S
@@ -0,0 +1,64 @@ 
+/*
+ * SPDX-License-Identifier: GPL-2.0
+ * Copyright (C) 2019 ARM Limited
+ */
+
+#include <asm/unistd.h>
+
+.section        ".rodata", "a"
+call_fmt:
+	.asciz "Calling sigreturn with fake sigframe sized:%zd at calculated SP @%08lX\n"
+
+.text
+
+.globl fake_sigreturn
+
+/*	fake_sigreturn	x0:&sigframe,  x1:sigframe_size,  x2:alignment_SP */
+fake_sigreturn:
+	mov x20, x0
+	mov x21, x1
+	mov x22, x2
+	mov x23, sp
+
+	/* 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
+
+	ldr x0, =call_fmt
+	mov x1, x21
+	mov x2, x23
+	bl printf
+
+	mov sp, x23
+
+	/* now fill it with the provided content... */
+	mov x0, sp
+	mov x1, x20
+	mov x2, x21
+	bl memcpy
+
+	/*
+	 * Here saving a last minute SP to current->token acts as a marker:
+	 * if we got here, we are successfully faking a sigreturn; in other
+	 * words we are sure no bad fatal signal has been raised till now
+	 * for unrelated reasons, so we should consider the possibl observed
+	 * fatal signal like SEGV coming from Kernel restore_sigframe() and
+	 * triggered as expected from our test-case.
+	 * For simplicity this assumes that current field 'token' is laid out
+	 * as first in struct tdescr
+	 */
+	ldr x0, current
+	str x23, [x0]
+	/* SP is already pointing back to the just built fake sigframe here */
+	mov x8, #__NR_rt_sigreturn
+	svc #0
+
+	/*
+	 * Above sigreturn should not return...looping here leads to a timeout
+	 * and ensure proper and clean test failure, instead of jumping around
+	 * on a potentially corrupted stack.
+	 */
+	b .
diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h
index ce35be8ebc8e..2a71da7e6695 100644
--- a/tools/testing/selftests/arm64/signal/test_signals_utils.h
+++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h
@@ -12,4 +12,5 @@  int test_run(struct tdescr *td);
 void test_result(struct tdescr *td);
 
 bool get_current_context(struct tdescr *td, ucontext_t *dest_uc);
+int fake_sigreturn(void *sigframe, size_t sz, int alignment);
 #endif
diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore
index a48a118b1a1a..0ea6fdc3765c 100644
--- a/tools/testing/selftests/arm64/signal/testcases/.gitignore
+++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore
@@ -4,3 +4,4 @@  mangle_pstate_invalid_mode_el1
 mangle_pstate_invalid_mode_el2
 mangle_pstate_invalid_mode_el3
 mangle_pstate_ssbs_regs
+fake_sigreturn_bad_magic
diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
new file mode 100644
index 000000000000..b4c063e02a7a
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c
@@ -0,0 +1,63 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2019 ARM Limited */
+
+#include <stdio.h>
+#include <ucontext.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+struct fake_sigframe sf;
+
+static int fake_sigreturn_bad_magic_run(struct tdescr *td,
+					siginfo_t *si, ucontext_t *uc)
+{
+	size_t resv_sz, offset;
+	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);
+	/*
+	 * find the terminator, preserving existing headers
+	 * and verify amount of spare room in __reserved area.
+	 */
+	head = get_terminator(shead, resv_sz, &offset);
+	/*
+	 * try stripping extra_context header when low on space:
+	 * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC
+	 * and the other for the usual terminator.
+	 */
+	if (head && resv_sz - offset < HDR_SZ * 2) {
+		fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n",
+			resv_sz - offset);
+		head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset);
+	}
+	/* just give up and timeout if still not enough space */
+	if (head && resv_sz - offset >= HDR_SZ) {
+		fprintf(stderr, "Mangling template header. Spare space:%zd\n",
+			resv_sz - offset);
+		/*
+		 * use a well known NON existent bad magic...something
+		 * we should pretty sure won't be ever defined in Kernel
+		 */
+		head->magic = KSFT_BAD_MAGIC;
+		head->size = HDR_SZ;
+		write_terminator_record(GET_RESV_NEXT_HEAD(head));
+
+		ASSERT_BAD_CONTEXT(&sf.uc);
+		fake_sigreturn(&sf, sizeof(sf), 16);
+	}
+
+	return 1;
+}
+
+struct tdescr tde = {
+		.name = "FAKE_SIGRETURN_BAD_MAGIC",
+		.descr = "Triggers a fake sigreturn with a sigframe including a bad non-existent magic",
+		.sig_ok = SIGSEGV,
+		.timeout = 3,
+		.run = fake_sigreturn_bad_magic_run,
+};