[PATCH stable 4.14 18/23] powerpc/64s: Wire up cpu_show_spectre_v2()

[Michael Ellerman]

Add a definition for cpu_show_spectre_v2() to override the generic
version. This has several permuations, though in practice some may not
occur we cater for any combination.

The most verbose is:

  Mitigation: Indirect branch serialisation (kernel only), Indirect
  branch cache disabled, ori31 speculation barrier enabled

We don't treat the ori31 speculation barrier as a mitigation on its
own, because it has to be *used* by code in order to be a mitigation
and we don't know if userspace is doing that. So if that's all we see
we say:

  Vulnerable, ori31 speculation barrier enabled

Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
(cherry picked from commit d6fbe1c55c55c6937cbea3531af7da84ab7473c3)
---
 arch/powerpc/kernel/security.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index 0eace3cac818..2cee3dcd231b 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -58,3 +58,36 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, c
 
 	return sprintf(buf, "Vulnerable\n");
 }
+
+ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	bool bcs, ccd, ori;
+	struct seq_buf s;
+
+	seq_buf_init(&s, buf, PAGE_SIZE - 1);
+
+	bcs = security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED);
+	ccd = security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED);
+	ori = security_ftr_enabled(SEC_FTR_SPEC_BAR_ORI31);
+
+	if (bcs || ccd) {
+		seq_buf_printf(&s, "Mitigation: ");
+
+		if (bcs)
+			seq_buf_printf(&s, "Indirect branch serialisation (kernel only)");
+
+		if (bcs && ccd)
+			seq_buf_printf(&s, ", ");
+
+		if (ccd)
+			seq_buf_printf(&s, "Indirect branch cache disabled");
+	} else
+		seq_buf_printf(&s, "Vulnerable");
+
+	if (ori)
+		seq_buf_printf(&s, ", ori31 speculation barrier enabled");
+
+	seq_buf_printf(&s, "\n");
+
+	return s.len;
+}
-- 
2.14.1