Messages in this thread | | | From | Alexander Shishkin <> | Subject | Re: [PATCH 2/2] perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems | Date | Fri, 28 Aug 2015 12:40:10 +0300 |
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Ingo Molnar <mingo@kernel.org> writes:
> * Alexander Shishkin <alexander.shishkin@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.shishkin@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
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