Re: [PATCH v3 5/5] kselftest: vm: Add tests for no-inherit memory-deny-write-execute

[Kees Cook]

On Tue, Jul 04, 2023 at 05:36:29PM +0200, Florent Revest wrote:
> Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
> PR_SET_MDWE prctl.
> 
> Check that:
> - it can't be set without PR_SET_MDWE
> - MDWE flags can't be unset
> - when set, PR_SET_MDWE doesn't propagate to children

I love more self tests! :)

> 
> Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
> ---
>  tools/testing/selftests/mm/mdwe_test.c | 98 ++++++++++++++++++++++++--
>  1 file changed, 92 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/mdwe_test.c b/tools/testing/selftests/mm/mdwe_test.c
> index 91aa9c3099e7..7bfc98bf9baa 100644
> --- a/tools/testing/selftests/mm/mdwe_test.c
> +++ b/tools/testing/selftests/mm/mdwe_test.c
> @@ -22,6 +22,8 @@
>  
>  TEST(prctl_flags)
>  {
> +	EXPECT_LT(prctl(PR_SET_MDWE, PR_MDWE_NO_INHERIT, 0L, 0L, 7L), 0);
> +

An existing issue, but I think the errno should be checked for each
of these...

>  	EXPECT_LT(prctl(PR_SET_MDWE, 7L, 0L, 0L, 0L), 0);
>  	EXPECT_LT(prctl(PR_SET_MDWE, 0L, 7L, 0L, 0L), 0);
>  	EXPECT_LT(prctl(PR_SET_MDWE, 0L, 0L, 7L, 0L), 0);
> @@ -33,6 +35,69 @@ TEST(prctl_flags)
>  	EXPECT_LT(prctl(PR_GET_MDWE, 0L, 0L, 0L, 7L), 0);
>  }
>  
> +FIXTURE(consecutive_prctl_flags) {};
> +FIXTURE_SETUP(consecutive_prctl_flags) {}
> +FIXTURE_TEARDOWN(consecutive_prctl_flags) {}
> +
> +FIXTURE_VARIANT(consecutive_prctl_flags)
> +{
> +	unsigned long first_flags;
> +	unsigned long second_flags;
> +	bool should_work;
> +};
> +
> +FIXTURE_VARIANT_ADD(consecutive_prctl_flags, same)
> +{
> +	.first_flags = PR_MDWE_REFUSE_EXEC_GAIN,
> +	.second_flags = PR_MDWE_REFUSE_EXEC_GAIN,
> +	.should_work = true,
> +};

I think two more variants should be added to get all the combinations:

FIXTURE_VARIANT_ADD(consecutive_prctl_no_flags, same)
{
	.first_flags = 0,
	.second_flags = 0,
	.should_work = true,
};

FIXTURE_VARIANT_ADD(consecutive_prctl_both_flags, same)
{
	.first_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
	.second_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
	.should_work = true,
};

> +
> +FIXTURE_VARIANT_ADD(consecutive_prctl_flags, cant_disable_mdwe)
> +{
> +	.first_flags = PR_MDWE_REFUSE_EXEC_GAIN,
> +	.second_flags = 0,
> +	.should_work = false,
> +};
> +
> +FIXTURE_VARIANT_ADD(consecutive_prctl_flags, cant_disable_mdwe_no_inherit)
> +{
> +	.first_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
> +	.second_flags = 0,
> +	.should_work = false,
> +};
> +
> +FIXTURE_VARIANT_ADD(consecutive_prctl_flags, cant_disable_no_inherit)
> +{
> +	.first_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
> +	.second_flags = PR_MDWE_REFUSE_EXEC_GAIN,
> +	.should_work = false,
> +};
> +
> +FIXTURE_VARIANT_ADD(consecutive_prctl_flags, cant_enable_no_inherit)
> +{
> +	.first_flags = PR_MDWE_REFUSE_EXEC_GAIN,
> +	.second_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
> +	.should_work = false,
> +};
> +
> +TEST_F(consecutive_prctl_flags, two_prctls)
> +{
> +	int ret;
> +
> +	EXPECT_EQ(prctl(PR_SET_MDWE, variant->first_flags, 0L, 0L, 0L), 0);
> +
> +	ret = prctl(PR_SET_MDWE, variant->second_flags, 0L, 0L, 0L);
> +	if (variant->should_work) {
> +		EXPECT_EQ(ret, 0);
> +
> +		ret = prctl(PR_GET_MDWE, 0L, 0L, 0L, 0L);
> +		ASSERT_EQ(ret, variant->second_flags);
> +	} else {
> +		EXPECT_NE(ret, 0);

Please test the expected errno value here.

> +	}
> +}
> +
>  FIXTURE(mdwe)
>  {
>  	void *p;
> @@ -45,28 +110,45 @@ FIXTURE_VARIANT(mdwe)
>  {
>  	bool enabled;
>  	bool forked;
> +	bool inherit;
>  };
>  
>  FIXTURE_VARIANT_ADD(mdwe, stock)
>  {
>  	.enabled = false,
>  	.forked = false,
> +	.inherit = false,
>  };
>  
>  FIXTURE_VARIANT_ADD(mdwe, enabled)
>  {
>  	.enabled = true,
>  	.forked = false,
> +	.inherit = true,
>  };
>  
> -FIXTURE_VARIANT_ADD(mdwe, forked)
> +FIXTURE_VARIANT_ADD(mdwe, inherited)
>  {
>  	.enabled = true,
>  	.forked = true,
> +	.inherit = true,
>  };
>  
> +FIXTURE_VARIANT_ADD(mdwe, not_inherited)
> +{
> +	.enabled = true,
> +	.forked = true,
> +	.inherit = false,
> +};
> +
> +static bool executable_map_should_fail(const FIXTURE_VARIANT(mdwe) *variant)
> +{
> +	return variant->enabled && (!variant->forked || variant->inherit);
> +}
> +
>  FIXTURE_SETUP(mdwe)
>  {
> +	unsigned long mdwe_flags;
>  	int ret, status;
>  
>  	self->p = NULL;
> @@ -76,13 +158,17 @@ FIXTURE_SETUP(mdwe)
>  	if (!variant->enabled)
>  		return;
>  
> -	ret = prctl(PR_SET_MDWE, PR_MDWE_REFUSE_EXEC_GAIN, 0L, 0L, 0L);
> +	mdwe_flags = PR_MDWE_REFUSE_EXEC_GAIN;
> +	if (!variant->inherit)
> +		mdwe_flags |= PR_MDWE_NO_INHERIT;
> +
> +	ret = prctl(PR_SET_MDWE, mdwe_flags, 0L, 0L, 0L);
>  	ASSERT_EQ(ret, 0) {
>  		TH_LOG("PR_SET_MDWE failed or unsupported");
>  	}
>  
>  	ret = prctl(PR_GET_MDWE, 0L, 0L, 0L, 0L);
> -	ASSERT_EQ(ret, 1);
> +	ASSERT_EQ(ret, mdwe_flags);
>  
>  	if (variant->forked) {
>  		self->pid = fork();
> @@ -113,7 +199,7 @@ TEST_F(mdwe, mmap_READ_EXEC)
>  TEST_F(mdwe, mmap_WRITE_EXEC)
>  {
>  	self->p = mmap(NULL, self->size, PROT_WRITE | PROT_EXEC, self->flags, 0, 0);
> -	if (variant->enabled) {
> +	if (executable_map_should_fail(variant)) {
>  		EXPECT_EQ(self->p, MAP_FAILED);
>  	} else {
>  		EXPECT_NE(self->p, MAP_FAILED);
> @@ -139,7 +225,7 @@ TEST_F(mdwe, mprotect_add_EXEC)
>  	ASSERT_NE(self->p, MAP_FAILED);
>  
>  	ret = mprotect(self->p, self->size, PROT_READ | PROT_EXEC);
> -	if (variant->enabled) {
> +	if (executable_map_should_fail(variant)) {
>  		EXPECT_LT(ret, 0);
>  	} else {
>  		EXPECT_EQ(ret, 0);
> @@ -154,7 +240,7 @@ TEST_F(mdwe, mprotect_WRITE_EXEC)
>  	ASSERT_NE(self->p, MAP_FAILED);
>  
>  	ret = mprotect(self->p, self->size, PROT_WRITE | PROT_EXEC);
> -	if (variant->enabled) {
> +	if (executable_map_should_fail(variant)) {
>  		EXPECT_LT(ret, 0);
>  	} else {
>  		EXPECT_EQ(ret, 0);
> -- 
> 2.41.0.255.g8b1d071c50-goog
> 

Otherwise looks good to me!

-- 
Kees Cook