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SubjectRe: [PATCH v4 7/7] selftests: test uaccess logging
On Thu, Dec 09, 2021 at 02:15PM -0800, Peter Collingbourne wrote:
> Add a kselftest for the uaccess logging feature.
>
> Link: https://linux-review.googlesource.com/id/I39e1707fb8aef53747c42bd55b46ecaa67205199
> Signed-off-by: Peter Collingbourne <pcc@google.com>

It would be good to also test:

- Logging of reads.

- Exhausting the uaccess buffer, ideally somehow checking that
the kernel hasn't written out-of-bounds, e.g. by using some
canary.

- Passing an invalid address to some syscall, for which the
access should not be logged?

- Passing an invalid address to the
PR_SET_UACCESS_DESCRIPTOR_ADDR_ADDR prctl().

- Passing a valid address to the prctl(), but that address
points to an invalid address.

> ---
> tools/testing/selftests/Makefile | 1 +
> .../testing/selftests/uaccess_buffer/Makefile | 4 +
> .../uaccess_buffer/uaccess_buffer_test.c | 126 ++++++++++++++++++
> 3 files changed, 131 insertions(+)
> create mode 100644 tools/testing/selftests/uaccess_buffer/Makefile
> create mode 100644 tools/testing/selftests/uaccess_buffer/uaccess_buffer_test.c
>
> diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
> index c852eb40c4f7..291b62430557 100644
> --- a/tools/testing/selftests/Makefile
> +++ b/tools/testing/selftests/Makefile
> @@ -71,6 +71,7 @@ TARGETS += timers
> endif
> TARGETS += tmpfs
> TARGETS += tpm2
> +TARGETS += uaccess_buffer
> TARGETS += user
> TARGETS += vDSO
> TARGETS += vm
> diff --git a/tools/testing/selftests/uaccess_buffer/Makefile b/tools/testing/selftests/uaccess_buffer/Makefile
> new file mode 100644
> index 000000000000..e6e5fb43ce29
> --- /dev/null
> +++ b/tools/testing/selftests/uaccess_buffer/Makefile
> @@ -0,0 +1,4 @@
> +# SPDX-License-Identifier: GPL-2.0
> +TEST_GEN_PROGS := uaccess_buffer_test
> +
> +include ../lib.mk
> diff --git a/tools/testing/selftests/uaccess_buffer/uaccess_buffer_test.c b/tools/testing/selftests/uaccess_buffer/uaccess_buffer_test.c
> new file mode 100644
> index 000000000000..051062e4fbf9
> --- /dev/null
> +++ b/tools/testing/selftests/uaccess_buffer/uaccess_buffer_test.c
> @@ -0,0 +1,126 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include "../kselftest_harness.h"
> +
> +#include <linux/uaccess-buffer.h>
> +#include <sys/prctl.h>
> +#include <sys/utsname.h>
> +
> +FIXTURE(uaccess_buffer)
> +{
> + uint64_t addr;
> +};
> +
> +FIXTURE_SETUP(uaccess_buffer)
> +{
> + ASSERT_EQ(0, prctl(PR_SET_UACCESS_DESCRIPTOR_ADDR_ADDR, &self->addr, 0,
> + 0, 0));
> +}
> +
> +FIXTURE_TEARDOWN(uaccess_buffer)
> +{
> + ASSERT_EQ(0, prctl(PR_SET_UACCESS_DESCRIPTOR_ADDR_ADDR, 0, 0, 0, 0));
> +}
> +
> +TEST_F(uaccess_buffer, uname)
> +{
> + struct uaccess_descriptor desc;
> + struct uaccess_buffer_entry entries[64];
> + struct utsname un;
> +
> + desc.addr = (uint64_t)(unsigned long)entries;
> + desc.size = 64;
> + self->addr = (uint64_t)(unsigned long)&desc;
> + ASSERT_EQ(0, uname(&un));
> + ASSERT_EQ(0, self->addr);
> +
> + if (desc.size == 63) {
> + ASSERT_EQ((uint64_t)(unsigned long)(entries + 1), desc.addr);
> +
> + ASSERT_EQ((uint64_t)(unsigned long)&un, entries[0].addr);
> + ASSERT_EQ(sizeof(struct utsname), entries[0].size);
> + ASSERT_EQ(UACCESS_BUFFER_FLAG_WRITE, entries[0].flags);
> + } else {
> + /* See override_architecture in kernel/sys.c */
> + ASSERT_EQ(62, desc.size);
> + ASSERT_EQ((uint64_t)(unsigned long)(entries + 2), desc.addr);
> +
> + ASSERT_EQ((uint64_t)(unsigned long)&un, entries[0].addr);
> + ASSERT_EQ(sizeof(struct utsname), entries[0].size);
> + ASSERT_EQ(UACCESS_BUFFER_FLAG_WRITE, entries[0].flags);
> +
> + ASSERT_EQ((uint64_t)(unsigned long)&un.machine,
> + entries[1].addr);
> + ASSERT_EQ(UACCESS_BUFFER_FLAG_WRITE, entries[1].flags);
> + }
> +}
> +
> +static bool handled;
> +
> +static void usr1_handler(int signo)
> +{
> + handled = true;
> +}
> +
> +TEST_F(uaccess_buffer, blocked_signals)
> +{
> + struct uaccess_descriptor desc;
> + struct shared_buf {
> + bool ready;
> + bool killed;
> + } volatile *shared = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE,
> + MAP_ANON | MAP_SHARED, -1, 0);

I know it's a synonym, but to be consistent with other code, MAP_ANONYMOUS?

> + struct sigaction act = {}, oldact;
> + int pid;
> +
> + handled = false;
> + act.sa_handler = usr1_handler;
> + sigaction(SIGUSR1, &act, &oldact);
> +
> + pid = fork();
> + if (pid == 0) {
> + /*
> + * Busy loop to synchronize instead of issuing syscalls because
> + * we need to test the behavior in the case where no syscall is
> + * issued by the parent process.
> + */
> + while (!shared->ready)
> + ;
> + kill(getppid(), SIGUSR1);
> + shared->killed = true;
> + _exit(0);
> + } else {
> + int i;
> +
> + desc.addr = 0;
> + desc.size = 0;
> + self->addr = (uint64_t)(unsigned long)&desc;
> +
> + shared->ready = true;
> + while (!shared->killed)
> + ;
> +
> + /*
> + * The kernel should have IPI'd us by now, but let's wait a bit
> + * longer just in case.

Is IPI = signalled? Because in the kernel, IPI = inter-processor
interrupt.

> + */
> + for (i = 0; i != 1000000; ++i)
> + ;

This is probably optimized out. usleep() should work, or add compiler
barrier if usleep doesn't work.

> +
> + ASSERT_FALSE(handled);
> +
> + /*
> + * Returning from the waitpid syscall should trigger the signal
> + * handler. The signal itself may also interrupt waitpid, so
> + * make sure to handle EINTR.
> + */
> + while (waitpid(pid, NULL, 0) == -1)
> + ASSERT_EQ(EINTR, errno);
> + ASSERT_TRUE(handled);
> + }
> +
> + munmap((void *)shared, getpagesize());
> + sigaction(SIGUSR1, &oldact, NULL);
> +}
> +
> +TEST_HARNESS_MAIN
> --
> 2.34.1.173.g76aa8bc2d0-goog
>

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