Re: [PATCHv5 bpf-next 7/8] selftests/x86: Add return uprobe shadow stack test

Jiri Olsa
2024-05-13T21:28:25Z

On Mon, May 13, 2024 at 06:45:07PM +0900, Masami Hiramatsu wrote:
> On Tue, 7 May 2024 12:53:20 +0200
> Jiri Olsa <jolsa@kernel.org> wrote:
>
> > Adding return uprobe test for shadow stack and making sure it's
> > working properly. Borrowed some of the code from bpf selftests.
>
> Hi Jiri,
>
> I can not find "SKIP" result in this change. If CONFIG_UPROBES=n,
> this should skip uprobe test.

ah it should be detected by parse_uint_from_file returning ENOENT
or something like that.. will add that

thanks,
jirka

>
> Thank you,
>
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > .../testing/selftests/x86/test_shadow_stack.c | 142 ++++++++++++++++++
> > 1 file changed, 142 insertions(+)
> >
> > diff --git a/tools/testing/selftests/x86/test_shadow_stack.c b/tools/testing/selftests/x86/test_shadow_stack.c
> > index 757e6527f67e..1b919baa999b 100644
> > --- a/tools/testing/selftests/x86/test_shadow_stack.c
> > +++ b/tools/testing/selftests/x86/test_shadow_stack.c
> > @@ -34,6 +34,7 @@
> > #include <sys/ptrace.h>
> > #include <sys/signal.h>
> > #include <linux/elf.h>
> > +#include <linux/perf_event.h>
> >
> > /*
> > * Define the ABI defines if needed, so people can run the tests
> > @@ -681,6 +682,141 @@ int test_32bit(void)
> > return !segv_triggered;
> > }
> >
> > +static int parse_uint_from_file(const char *file, const char *fmt)
> > +{
> > + int err, ret;
> > + FILE *f;
> > +
> > + f = fopen(file, "re");
> > + if (!f) {
> > + err = -errno;
> > + printf("failed to open '%s': %d\n", file, err);
> > + return err;
> > + }
> > + err = fscanf(f, fmt, &ret);
> > + if (err != 1) {
> > + err = err == EOF ? -EIO : -errno;
> > + printf("failed to parse '%s': %d\n", file, err);
> > + fclose(f);
> > + return err;
> > + }
> > + fclose(f);
> > + return ret;
> > +}
> > +
> > +static int determine_uprobe_perf_type(void)
> > +{
> > + const char *file = "/sys/bus/event_source/devices/uprobe/type";
> > +
> > + return parse_uint_from_file(file, "%d\n");
> > +}
> > +
> > +static int determine_uprobe_retprobe_bit(void)
> > +{
> > + const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";
> > +
> > + return parse_uint_from_file(file, "config:%d\n");
> > +}
> > +
> > +static ssize_t get_uprobe_offset(const void *addr)
> > +{
> > + size_t start, end, base;
> > + char buf[256];
> > + bool found = false;
> > + FILE *f;
> > +
> > + f = fopen("/proc/self/maps", "r");
> > + if (!f)
> > + return -errno;
> > +
> > + while (fscanf(f, "%zx-%zx %s %zx %*[^\n]\n", &start, &end, buf, &base) == 4) {
> > + if (buf[2] == 'x' && (uintptr_t)addr >= start && (uintptr_t)addr < end) {
> > + found = true;
> > + break;
> > + }
> > + }
> > +
> > + fclose(f);
> > +
> > + if (!found)
> > + return -ESRCH;
> > +
> > + return (uintptr_t)addr - start + base;
> > +}
> > +
> > +static __attribute__((noinline)) void uretprobe_trigger(void)
> > +{
> > + asm volatile ("");
> > +}
> > +
> > +/*
> > + * This test setups return uprobe, which is sensitive to shadow stack
> > + * (crashes without extra fix). After executing the uretprobe we fail
> > + * the test if we receive SIGSEGV, no crash means we're good.
> > + *
> > + * Helper functions above borrowed from bpf selftests.
> > + */
> > +static int test_uretprobe(void)
> > +{
> > + const size_t attr_sz = sizeof(struct perf_event_attr);
> > + const char *file = "/proc/self/exe";
> > + int bit, fd = 0, type, err = 1;
> > + struct perf_event_attr attr;
> > + struct sigaction sa = {};
> > + ssize_t offset;
> > +
> > + type = determine_uprobe_perf_type();
> > + if (type < 0)
> > + return 1;
> > +
> > + offset = get_uprobe_offset(uretprobe_trigger);
> > + if (offset < 0)
> > + return 1;
> > +
> > + bit = determine_uprobe_retprobe_bit();
> > + if (bit < 0)
> > + return 1;
> > +
> > + sa.sa_sigaction = segv_gp_handler;
> > + sa.sa_flags = SA_SIGINFO;
> > + if (sigaction(SIGSEGV, &sa, NULL))
> > + return 1;
> > +
> > + /* Setup return uprobe through perf event interface. */
> > + memset(&attr, 0, attr_sz);
> > + attr.size = attr_sz;
> > + attr.type = type;
> > + attr.config = 1 << bit;
> > + attr.config1 = (__u64) (unsigned long) file;
> > + attr.config2 = offset;
> > +
> > + fd = syscall(__NR_perf_event_open, &attr, 0 /* pid */, -1 /* cpu */,
> > + -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
> > + if (fd < 0)
> > + goto out;
> > +
> > + if (sigsetjmp(jmp_buffer, 1))
> > + goto out;
> > +
> > + ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK);
> > +
> > + /*
> > + * This either segfaults and goes through sigsetjmp above
> > + * or succeeds and we're good.
> > + */
> > + uretprobe_trigger();
> > +
> > + printf("[OK]\tUretprobe test\n");
> > + err = 0;
> > +
> > +out:
> > + ARCH_PRCTL(ARCH_SHSTK_DISABLE, ARCH_SHSTK_SHSTK);
> > + signal(SIGSEGV, SIG_DFL);
> > + if (fd)
> > + close(fd);
> > + return err;
> > +}
> > +
> > void segv_handler_ptrace(int signum, siginfo_t *si, void *uc)
> > {
> > /* The SSP adjustment caused a segfault. */
> > @@ -867,6 +1003,12 @@ int main(int argc, char *argv[])
> > goto out;
> > }
> >
> > + if (test_uretprobe()) {
> > + ret = 1;
> > + printf("[FAIL]\turetprobe test\n");
> > + goto out;
> > + }
> > +
> > return ret;
> >
> > out:
> > --
> > 2.44.0
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>