Re: [PATCH 2/2] perf/x86/intel/bts: Disallow use by unprivileged users on paranoid systems
From: Ingo Molnar
Date: Fri Aug 28 2015 - 01:31:38 EST
* Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> 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?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/