[PATCH stable v4.9 06/35] powerpc/64s: Enable barrier_nospec based on firmware settings

Michael Ellerman
2019-04-11T11:46:46Z

From: Michal Suchanek <msuchanek@suse.de>

commit cb3d6759a93c6d0aea1c10deb6d00e111c29c19c upstream.

Check what firmware told us and enable/disable the barrier_nospec as
appropriate.

We err on the side of enabling the barrier, as it's no-op on older
systems, see the comment for more detail.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/include/asm/setup.h | 1 +
arch/powerpc/kernel/security.c | 60 ++++++++++++++++++++++++++
arch/powerpc/platforms/powernv/setup.c | 1 +
arch/powerpc/platforms/pseries/setup.c | 1 +
4 files changed, 63 insertions(+)

diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h
index a225b5c42e76..84ae150ce6a6 100644
--- a/arch/powerpc/include/asm/setup.h
+++ b/arch/powerpc/include/asm/setup.h
@@ -51,6 +51,7 @@ enum l1d_flush_type {

void setup_rfi_flush(enum l1d_flush_type, bool enable);
void do_rfi_flush_fixups(enum l1d_flush_type types);
+void setup_barrier_nospec(void);
void do_barrier_nospec_fixups(bool enable);
extern bool barrier_nospec_enabled;

diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index 34d436fe2498..d0e974da4918 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -9,6 +9,7 @@
#include <linux/device.h>
#include <linux/seq_buf.h>

+#include <asm/debug.h>
#include <asm/security_features.h>
#include <asm/setup.h>

@@ -23,6 +24,65 @@ static void enable_barrier_nospec(bool enable)
do_barrier_nospec_fixups(enable);
}

+void setup_barrier_nospec(void)
+{
+ bool enable;
+
+ /*
+ * It would make sense to check SEC_FTR_SPEC_BAR_ORI31 below as well.
+ * But there's a good reason not to. The two flags we check below are
+ * both are enabled by default in the kernel, so if the hcall is not
+ * functional they will be enabled.
+ * On a system where the host firmware has been updated (so the ori
+ * functions as a barrier), but on which the hypervisor (KVM/Qemu) has
+ * not been updated, we would like to enable the barrier. Dropping the
+ * check for SEC_FTR_SPEC_BAR_ORI31 achieves that. The only downside is
+ * we potentially enable the barrier on systems where the host firmware
+ * is not updated, but that's harmless as it's a no-op.
+ */
+ enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
+ security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR);
+
+ enable_barrier_nospec(enable);
+}
+
+#ifdef CONFIG_DEBUG_FS
+static int barrier_nospec_set(void *data, u64 val)
+{
+ switch (val) {
+ case 0:
+ case 1:
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ if (!!val == !!barrier_nospec_enabled)
+ return 0;
+
+ enable_barrier_nospec(!!val);
+
+ return 0;
+}
+
+static int barrier_nospec_get(void *data, u64 *val)
+{
+ *val = barrier_nospec_enabled ? 1 : 0;
+ return 0;
+}
+
+DEFINE_SIMPLE_ATTRIBUTE(fops_barrier_nospec,
+ barrier_nospec_get, barrier_nospec_set, "%llu\n");
+
+static __init int barrier_nospec_debugfs_init(void)
+{
+ debugfs_create_file("barrier_nospec", 0600, powerpc_debugfs_root, NULL,
+ &fops_barrier_nospec);
+ return 0;
+}
+device_initcall(barrier_nospec_debugfs_init);
+#endif /* CONFIG_DEBUG_FS */
+
ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
{
bool thread_priv;
diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
index 17203abf38e8..eb5464648810 100644
--- a/arch/powerpc/platforms/powernv/setup.c
+++ b/arch/powerpc/platforms/powernv/setup.c
@@ -123,6 +123,7 @@ static void pnv_setup_rfi_flush(void)
security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV));

setup_rfi_flush(type, enable);
+ setup_barrier_nospec();
}

static void __init pnv_setup_arch(void)
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 91ade7755823..2b2759c98c7e 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -525,6 +525,7 @@ void pseries_setup_rfi_flush(void)
security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR);

setup_rfi_flush(types, enable);
+ setup_barrier_nospec();
}

static void __init pSeries_setup_arch(void)
--
2.20.1