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arm64: Advertise CPUs capable of running 32-bit applications in sysfs

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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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210730112443.23245-14-will@kernel.org
This commit is contained in:
Will Deacon 2021-07-30 12:24:40 +01:00 committed by Peter Zijlstra
parent df950811f4
commit 7af33504d1
2 changed files with 28 additions and 0 deletions
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9
Documentation/ABI/testing/sysfs-devices-system-cpu
View file

@ -494,6 +494,15 @@ 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: May 2021
Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
Description: Identifies the subset of CPUs in the system that can execute
AArch32 (32-bit ARM) applications. If present, the same format as
/sys/devices/system/cpu/{offline,online,possible,present} is used.
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@vger.kernel.org>

19
arch/arm64/kernel/cpufeature.c
View file

@ -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/minmax.h>
#include <linux/mm.h>
@ -1321,6 +1322,24 @@ const struct cpumask *system_32bit_el0_cpumask(void)
return cpu_possible_mask;
}
static ssize_t aarch32_el0_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
const struct cpumask *mask = system_32bit_el0_cpumask();
return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(mask));
}
static const DEVICE_ATTR_RO(aarch32_el0);
static int __init aarch32_el0_sysfs_init(void)
{
if (!allow_mismatched_32bit_el0)
return 0;
return device_create_file(cpu_subsys.dev_root, &dev_attr_aarch32_el0);
}
device_initcall(aarch32_el0_sysfs_init);
static bool has_32bit_el0(const struct arm64_cpu_capabilities *entry, int scope)
{
if (!has_cpuid_feature(entry, scope))