Re: [PATCH v4 7/7] selftests: test uaccess logging

[Marco Elver <elver@google.com>]

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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