As suggested on the list, https://lkml.org/lkml/2019/1/4/282, there are
a number of cases where its useful for a system to avoid exporting a
sysfs entry for a given vulnerability. This set adds an architecture
specific callback which returns the bitmap of vulnerabilities the
architecture would like to advertise.

Signed-off-by: Jeremy Linton <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Thomas Gleixner <redacted>
Cc: Josh Poimboeuf <redacted>
Cc: Konrad Rzeszutek Wilk <redacted>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Andi Kleen <redacted>
Cc: Jiri Kosina <redacted>
---
  drivers/base/cpu.c  | 19 +++++++++++++++++++
  include/linux/cpu.h |  7 +++++++
  2 files changed, 26 insertions(+)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index eb9443d5bae1..35f6dfb24cd6 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c

@@ -561,6 +561,11 @@ static struct attribute *cpu_root_vulnerabilities_attrs[] = {
  	NULL
  };
  
+uint __weak arch_supported_vuln_attr_fields(void)
+{
+	return VULN_MELTDOWN|VULN_SPECTREV1|VULN_SPECTREV2|VULN_SSB|VULN_L1TF;
+}
+
  static const struct attribute_group cpu_root_vulnerabilities_group = {
  	.name  = "vulnerabilities",
  	.attrs = cpu_root_vulnerabilities_attrs,

@@ -568,6 +573,20 @@ static const struct attribute_group cpu_root_vulnerabilities_group = {
  
  static void __init cpu_register_vulnerabilities(void)
  {
+	int fld;
+	int max_fields = ARRAY_SIZE(cpu_root_vulnerabilities_attrs) - 1;
+	struct attribute **hd = cpu_root_vulnerabilities_attrs;
+	uint enabled_fields = arch_supported_vuln_attr_fields();
+
+	/* only enable entries requested by the arch code */
+	for (fld = 0; fld < max_fields; fld++) {
+		if (enabled_fields & 1 << fld) {
+			*hd = cpu_root_vulnerabilities_attrs[fld];
+			hd++;
+		}
+	}
+	*hd = NULL;
+

  	if (sysfs_create_group(&cpu_subsys.dev_root->kobj,
  			       &cpu_root_vulnerabilities_group))
  		pr_err("Unable to register CPU vulnerabilities\n");

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 218df7f4d3e1..5e45814bcc24 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h

@@ -189,4 +189,11 @@ static inline void cpu_smt_check_topology_early(void) { }
  static inline void cpu_smt_check_topology(void) { }
  #endif
  
+/* generic cpu vulnerability attributes */
+#define VULN_MELTDOWN  0x01
+#define VULN_SPECTREV1 0x02
+#define VULN_SPECTREV2 0x04
+#define VULN_SSB       0x08
+#define VULN_L1TF      0x10