| Message ID | 1512563739-25239-19-git-send-email-will.deacon@arm.com |
|---|---|
| State | Accepted |
| Commit | 7a4a0c1555b824e0d3dd72942481b1190abea604 |
| Headers | show |
| Series | arm64: Unmap the kernel whilst running in userspace (KPTI) | expand |
On Wed, Dec 06, 2017 at 12:35:37PM +0000, Will Deacon wrote: > When running with the kernel unmapped whilst at EL0, the virtually-addressed > SPE buffer is also unmapped, which can lead to buffer faults if userspace > profiling is enabled and potentially also when writing back kernel samples > unless an expensive drain operation is performed on exception return. > > For now, fail the SPE driver probe when arm64_kernel_unmapped_at_el0(). > > Signed-off-by: Will Deacon <will.deacon@arm.com> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Mark. > --- > drivers/perf/arm_spe_pmu.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c > index 8ce262fc2561..51b40aecb776 100644 > --- a/drivers/perf/arm_spe_pmu.c > +++ b/drivers/perf/arm_spe_pmu.c > @@ -1164,6 +1164,15 @@ static int arm_spe_pmu_device_dt_probe(struct platform_device *pdev) > struct arm_spe_pmu *spe_pmu; > struct device *dev = &pdev->dev; > > + /* > + * If kernelspace is unmapped when running at EL0, then the SPE > + * buffer will fault and prematurely terminate the AUX session. > + */ > + if (arm64_kernel_unmapped_at_el0()) { > + dev_warn_once(dev, "profiling buffer inaccessible. Try passing \"kpti=off\" on the kernel command line\n"); > + return -EPERM; > + } > + > spe_pmu = devm_kzalloc(dev, sizeof(*spe_pmu), GFP_KERNEL); > if (!spe_pmu) { > dev_err(dev, "failed to allocate spe_pmu\n"); > -- > 2.1.4 >
diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c index 8ce262fc2561..51b40aecb776 100644 --- a/drivers/perf/arm_spe_pmu.c +++ b/drivers/perf/arm_spe_pmu.c @@ -1164,6 +1164,15 @@ static int arm_spe_pmu_device_dt_probe(struct platform_device *pdev) struct arm_spe_pmu *spe_pmu; struct device *dev = &pdev->dev; + /* + * If kernelspace is unmapped when running at EL0, then the SPE + * buffer will fault and prematurely terminate the AUX session. + */ + if (arm64_kernel_unmapped_at_el0()) { + dev_warn_once(dev, "profiling buffer inaccessible. Try passing \"kpti=off\" on the kernel command line\n"); + return -EPERM; + } + spe_pmu = devm_kzalloc(dev, sizeof(*spe_pmu), GFP_KERNEL); if (!spe_pmu) { dev_err(dev, "failed to allocate spe_pmu\n");
When running with the kernel unmapped whilst at EL0, the virtually-addressed SPE buffer is also unmapped, which can lead to buffer faults if userspace profiling is enabled and potentially also when writing back kernel samples unless an expensive drain operation is performed on exception return. For now, fail the SPE driver probe when arm64_kernel_unmapped_at_el0(). Signed-off-by: Will Deacon <will.deacon@arm.com> --- drivers/perf/arm_spe_pmu.c | 9 +++++++++ 1 file changed, 9 insertions(+) -- 2.1.4