Since 32-bit applications will be killed if they are caught trying to
execute on a 64-bit-only CPU in a mismatched system, advertise the set
of 32-bit capable CPUs to userspace in sysfs.
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
.../ABI/testing/sysfs-devices-system-cpu | 8 ++++++++
arch/arm64/kernel/cpufeature.c | 19 +++++++++++++++++++
2 files changed, 27 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index b555df825447..19893fb8e870 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -472,6 +472,14 @@ Description: AArch64 CPU registers
'identification' directory exposes the CPU ID registers for
identifying model and revision of the CPU.
+What: /sys/devices/system/cpu/aarch32_el0
+Date: October 2020
+Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>
+Description: Identifies the subset of CPUs in the system that can execute
+ AArch32 (32-bit ARM) applications. If absent, then all or none
+ of the CPUs can execute AArch32 applications and execve() will
+ behave accordingly.
+
What: /sys/devices/system/cpu/cpu#/cpu_capacity
Date: December 2016
Contact: Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 2e2219cbd54c..9f29d4d1ef7e 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -67,6 +67,7 @@
#include <linux/crash_dump.h>
#include <linux/sort.h>
#include <linux/stop_machine.h>
+#include <linux/sysfs.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/cpu.h>
@@ -1236,6 +1237,24 @@ bool system_has_mismatched_32bit_el0(void)
return fld == ID_AA64PFR0_EL0_64BIT_ONLY;
}
+static ssize_t aarch32_el0_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ const struct cpumask *mask = system_32bit_el0_cpumask();
+ return sprintf(buf, "%*pbl\n", cpumask_pr_args(mask));
+}
+static const struct kobj_attribute aarch32_el0_attr = __ATTR_RO(aarch32_el0);
+
+static int __init aarch32_el0_sysfs_init(void)
+{
+ if (!__allow_mismatched_32bit_el0)
+ return 0;
+
+ return sysfs_create_file(&cpu_subsys.dev_root->kobj,
+ &aarch32_el0_attr.attr);
+}
+device_initcall(aarch32_el0_sysfs_init);
+
static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
{
return has_cpuid_feature(entry, scope) || __allow_mismatched_32bit_el0;
--
2.29.0.rc2.309.g374f81d7ae-goog
