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Message-ID: <202308251538.F716651@keescook>
Date: Fri, 25 Aug 2023 15:45:57 -0700
From: Kees Cook <keescook@...omium.org>
To: Florent Revest <revest@...omium.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
akpm@...ux-foundation.org, catalin.marinas@....com,
anshuman.khandual@....com, joey.gouly@....com, mhocko@...e.com,
david@...hat.com, peterx@...hat.com, izbyshev@...ras.ru,
broonie@...nel.org, szabolcs.nagy@....com, kpsingh@...nel.org,
gthelen@...gle.com, toiwoton@...il.com
Subject: Re: [PATCH v3 5/5] kselftest: vm: Add tests for no-inherit
memory-deny-write-execute
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@...omium.org>
> ---
> 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
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