Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
PR_SET_MDWE prctl.
Signed-off-by: Florent Revest <[email protected]>
---
tools/testing/selftests/mm/mdwe_test.c | 95 ++++++++++++++++++++++++--
1 file changed, 89 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/mm/mdwe_test.c b/tools/testing/selftests/mm/mdwe_test.c
index 91aa9c3099e7..9f08ed1b99ae 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);
+
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 +35,66 @@ 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,
+};
+
+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, can_lower_privileges)
+{
+ .first_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
+ .second_flags = PR_MDWE_REFUSE_EXEC_GAIN,
+ .should_work = true,
+};
+
+FIXTURE_VARIANT_ADD(consecutive_prctl_flags, cant_gain_privileges)
+{
+ .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);
+ } else {
+ EXPECT_NE(ret, 0);
+ }
+}
+
FIXTURE(mdwe)
{
void *p;
@@ -45,28 +107,45 @@ 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 +155,17 @@ 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 +196,7 @@ 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 +222,7 @@ 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 +237,7 @@ 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);
--
2.40.1.495.gc816e09b53d-goog
On 2023-05-04 20:09, Florent Revest wrote:
> Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
> PR_SET_MDWE prctl.
>
> Signed-off-by: Florent Revest <[email protected]>
> ---
> tools/testing/selftests/mm/mdwe_test.c | 95 ++++++++++++++++++++++++--
> 1 file changed, 89 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/mdwe_test.c
> b/tools/testing/selftests/mm/mdwe_test.c
> index 91aa9c3099e7..9f08ed1b99ae 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);
> +
PR_MDWE_NO_INHERIT is defined to an int constant, so passing it to
prctl() without a cast to long or similar may produce wrong code on
64-bit targets (ABIs typically don't require the compiler to clear the
upper 32 bits of a 64-bit register when passing a 32-bit argument, so
va_arg(arg, unsigned long) in prctl() implementation might get junk).
Arguably, defining PR_MDWE_* to plain int constants is a bug, or at
least a footgun for users of uapi headers.
Thanks,
Alexey
> 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 +35,66 @@ 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,
> +};
> +
> +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, can_lower_privileges)
> +{
> + .first_flags = PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT,
> + .second_flags = PR_MDWE_REFUSE_EXEC_GAIN,
> + .should_work = true,
> +};
> +
> +FIXTURE_VARIANT_ADD(consecutive_prctl_flags, cant_gain_privileges)
> +{
> + .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);
> + } else {
> + EXPECT_NE(ret, 0);
> + }
> +}
> +
> FIXTURE(mdwe)
> {
> void *p;
> @@ -45,28 +107,45 @@ 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 +155,17 @@ 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 +196,7 @@ 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 +222,7 @@ 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 +237,7 @@ 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);
On Thu, May 4, 2023 at 10:30 PM Alexey Izbyshev <[email protected]> wrote:
>
> On 2023-05-04 20:09, Florent Revest wrote:
> > Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
> > PR_SET_MDWE prctl.
> >
> > Signed-off-by: Florent Revest <[email protected]>
> > ---
> > tools/testing/selftests/mm/mdwe_test.c | 95 ++++++++++++++++++++++++--
> > 1 file changed, 89 insertions(+), 6 deletions(-)
> >
> > diff --git a/tools/testing/selftests/mm/mdwe_test.c
> > b/tools/testing/selftests/mm/mdwe_test.c
> > index 91aa9c3099e7..9f08ed1b99ae 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);
> > +
>
> PR_MDWE_NO_INHERIT is defined to an int constant, so passing it to
> prctl() without a cast to long or similar may produce wrong code on
> 64-bit targets (ABIs typically don't require the compiler to clear the
> upper 32 bits of a 64-bit register when passing a 32-bit argument, so
> va_arg(arg, unsigned long) in prctl() implementation might get junk).
Ah, good catch Alexey! :)
> Arguably, defining PR_MDWE_* to plain int constants is a bug, or at
> least a footgun for users of uapi headers.
As part of the next version of this series, I'm happy to:
1- change the existing PR_MDWE_REFUSE_EXEC_GAIN to 1UL
2- introduce PR_MDWE_NO_INHERIT as 2UL
But I'm surprised that most of the macros in
include/uapi/linux/prctl.h are the same sort of footguns already ?
Hasn't it been an issue for other prctls yet ?
On 2023-05-05 19:42, Florent Revest wrote:
> On Thu, May 4, 2023 at 10:30 PM Alexey Izbyshev <[email protected]>
> wrote:
>>
>> On 2023-05-04 20:09, Florent Revest wrote:
>> > Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
>> > PR_SET_MDWE prctl.
>> >
>> > Signed-off-by: Florent Revest <[email protected]>
>> > ---
>> > tools/testing/selftests/mm/mdwe_test.c | 95 ++++++++++++++++++++++++--
>> > 1 file changed, 89 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/tools/testing/selftests/mm/mdwe_test.c
>> > b/tools/testing/selftests/mm/mdwe_test.c
>> > index 91aa9c3099e7..9f08ed1b99ae 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);
>> > +
>>
>> PR_MDWE_NO_INHERIT is defined to an int constant, so passing it to
>> prctl() without a cast to long or similar may produce wrong code on
>> 64-bit targets (ABIs typically don't require the compiler to clear the
>> upper 32 bits of a 64-bit register when passing a 32-bit argument, so
>> va_arg(arg, unsigned long) in prctl() implementation might get junk).
>
> Ah, good catch Alexey! :)
>
>> Arguably, defining PR_MDWE_* to plain int constants is a bug, or at
>> least a footgun for users of uapi headers.
>
> As part of the next version of this series, I'm happy to:
> 1- change the existing PR_MDWE_REFUSE_EXEC_GAIN to 1UL
> 2- introduce PR_MDWE_NO_INHERIT as 2UL
>
Yes, I think it's the right thing to do. I suggest to spell them as (1UL
<< 0), etc. for consistency with all other unsigned long flags in the
header.
> But I'm surprised that most of the macros in
> include/uapi/linux/prctl.h are the same sort of footguns already ?
> Hasn't it been an issue for other prctls yet ?
Yes, they are. I'm not aware of a public discussion of this specific
issue, but note that at least for some prctl() options the kernel
doesn't care about upper bits because arguments are truncated before
doing anything else with them (e.g. for PR_SCHED_CORE raw prctl()
arguments are implicitly converted to what sched_core_share_pid()
expects). Also, actually getting junk in the upper bits might not always
be easy (e.g. on x86-64 all or almost all instructions with r32
destination operand clear the upper bits). Unfortunately, I don't have a
better answer than this.
Alexey
On Fri, May 5, 2023 at 11:26 PM Alexey Izbyshev <[email protected]> wrote:
>
> On 2023-05-05 19:42, Florent Revest wrote:
> > On Thu, May 4, 2023 at 10:30 PM Alexey Izbyshev <[email protected]>
> > wrote:
> >>
> >> On 2023-05-04 20:09, Florent Revest wrote:
> >> > Add some tests to cover the new PR_MDWE_NO_INHERIT flag of the
> >> > PR_SET_MDWE prctl.
> >> >
> >> > Signed-off-by: Florent Revest <[email protected]>
> >> > ---
> >> > tools/testing/selftests/mm/mdwe_test.c | 95 ++++++++++++++++++++++++--
> >> > 1 file changed, 89 insertions(+), 6 deletions(-)
> >> >
> >> > diff --git a/tools/testing/selftests/mm/mdwe_test.c
> >> > b/tools/testing/selftests/mm/mdwe_test.c
> >> > index 91aa9c3099e7..9f08ed1b99ae 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);
> >> > +
> >>
> >> PR_MDWE_NO_INHERIT is defined to an int constant, so passing it to
> >> prctl() without a cast to long or similar may produce wrong code on
> >> 64-bit targets (ABIs typically don't require the compiler to clear the
> >> upper 32 bits of a 64-bit register when passing a 32-bit argument, so
> >> va_arg(arg, unsigned long) in prctl() implementation might get junk).
> >
> > Ah, good catch Alexey! :)
> >
> >> Arguably, defining PR_MDWE_* to plain int constants is a bug, or at
> >> least a footgun for users of uapi headers.
> >
> > As part of the next version of this series, I'm happy to:
> > 1- change the existing PR_MDWE_REFUSE_EXEC_GAIN to 1UL
> > 2- introduce PR_MDWE_NO_INHERIT as 2UL
> >
> Yes, I think it's the right thing to do. I suggest to spell them as (1UL
> << 0), etc. for consistency with all other unsigned long flags in the
> header.
Ah yeah, absolutely! Good tip too, thank you :)
> > But I'm surprised that most of the macros in
> > include/uapi/linux/prctl.h are the same sort of footguns already ?
> > Hasn't it been an issue for other prctls yet ?
>
> Yes, they are. I'm not aware of a public discussion of this specific
> issue, but note that at least for some prctl() options the kernel
> doesn't care about upper bits because arguments are truncated before
> doing anything else with them (e.g. for PR_SCHED_CORE raw prctl()
That makes sense
> arguments are implicitly converted to what sched_core_share_pid()
> expects). Also, actually getting junk in the upper bits might not always
> be easy (e.g. on x86-64 all or almost all instructions with r32
> destination operand clear the upper bits). Unfortunately, I don't have a
> better answer than this.
Okay, I was just curious, that's good to know