Ingo Molnar <mi...@kernel.org> writes: > * Alexander Shishkin <alexander.shish...@linux.intel.com> wrote: > >> BTS leaks kernel addresses even in userspace-only mode due to imprecise IP >> sampling, so sometimes syscall entry points or page fault handler addresses >> end up in a userspace trace. >> >> Now, intel_bts driver exports trace data zero-copy, it does not scan through >> it to filter out the kernel addresses and it's would be a O(n) job. >> >> To work around this situation, this patch forbids the use of intel_bts >> driver by unprivileged users with paranoid setting higher than 1, which >> forbids kernel tracing. >> >> Signed-off-by: Alexander Shishkin <alexander.shish...@linux.intel.com> >> --- >> arch/x86/kernel/cpu/perf_event_intel_bts.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/arch/x86/kernel/cpu/perf_event_intel_bts.c >> b/arch/x86/kernel/cpu/perf_event_intel_bts.c >> index 80df16e020..4f6daff92d 100644 >> --- a/arch/x86/kernel/cpu/perf_event_intel_bts.c >> +++ b/arch/x86/kernel/cpu/perf_event_intel_bts.c >> @@ -495,6 +495,16 @@ static int bts_event_init(struct perf_event *event) >> if (x86_add_exclusive(x86_lbr_exclusive_bts)) >> return -EBUSY; >> >> + /* >> + * BTS leaks kernel addresses even when CPL0 tracing is >> + * disabled, so disallow intel_bts driver for unprivileged >> + * users on paranoid systems since it provides trace data >> + * to the user in a zero-copy fashion. >> + */ >> + if (event->attr.exclude_kernel && perf_paranoid_kernel() && >> + !capable(CAP_SYS_ADMIN)) >> + return -EACCES; > > I.e. it's disabled by default as well, with default paranoia settings?
Actually no, the kernel's default is 1, which allows kernel profiling for unprivileged users. Distros might be more strict though. Regards, -- Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
