From df950811f4a884d08f05e22a8e0089d54bb4ba70 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 30 Jul 2021 12:24:39 +0100 Subject: arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system If we want to support 32-bit applications, then when we identify a CPU with mismatched 32-bit EL0 support we must ensure that we will always have an active 32-bit CPU available to us from then on. This is important for the scheduler, because is_cpu_allowed() will be constrained to 32-bit CPUs for compat tasks and forced migration due to a hotplug event will hang if no 32-bit CPUs are available. On detecting a mismatch, prevent offlining of either the mismatching CPU if it is 32-bit capable, or find the first active 32-bit capable CPU otherwise. Signed-off-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20210730112443.23245-13-will@kernel.org --- arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) (limited to 'arch/arm64/kernel/cpufeature.c') diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 0ead8bfedf20..0af584549499 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -2901,15 +2901,38 @@ void __init setup_cpu_features(void) static int enable_mismatched_32bit_el0(unsigned int cpu) { + /* + * The first 32-bit-capable CPU we detected and so can no longer + * be offlined by userspace. -1 indicates we haven't yet onlined + * a 32-bit-capable CPU. + */ + static int lucky_winner = -1; + struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu); bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0); if (cpu_32bit) { cpumask_set_cpu(cpu, cpu_32bit_el0_mask); static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0); - setup_elf_hwcaps(compat_elf_hwcaps); } + if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit) + return 0; + + if (lucky_winner >= 0) + return 0; + + /* + * We've detected a mismatch. We need to keep one of our CPUs with + * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting + * every CPU in the system for a 32-bit task. + */ + lucky_winner = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask, + cpu_active_mask); + get_cpu_device(lucky_winner)->offline_disabled = true; + setup_elf_hwcaps(compat_elf_hwcaps); + pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n", + cpu, lucky_winner); return 0; } -- cgit v1.2.3 From 7af33504d1c8077b40121294b5eb6e680a859468 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 30 Jul 2021 12:24:40 +0100 Subject: arm64: Advertise CPUs capable of running 32-bit applications in sysfs 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Greg Kroah-Hartman Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20210730112443.23245-14-will@kernel.org --- Documentation/ABI/testing/sysfs-devices-system-cpu | 9 +++++++++ arch/arm64/kernel/cpufeature.c | 19 +++++++++++++++++++ 2 files changed, 28 insertions(+) (limited to 'arch/arm64/kernel/cpufeature.c') diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 160b10c029c0..69edbd99e0b7 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -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 +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 diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 0af584549499..0a9bc7eff26e 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -67,6 +67,7 @@ #include #include #include +#include #include #include #include @@ -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)) -- cgit v1.2.3 From ead7de462ae56b2d2e56fb5a414f6e916dddc4c9 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 30 Jul 2021 12:24:41 +0100 Subject: arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Allow systems with mismatched 32-bit support at EL0 to run 32-bit applications based on a new kernel parameter. Signed-off-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20210730112443.23245-15-will@kernel.org --- Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ arch/arm64/kernel/cpufeature.c | 7 +++++++ 2 files changed, 15 insertions(+) (limited to 'arch/arm64/kernel/cpufeature.c') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index bdb22006f713..6ab625dea8c0 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -287,6 +287,14 @@ do not want to use tracing_snapshot_alloc() as it needs to be done where GFP_KERNEL allocations are allowed. + allow_mismatched_32bit_el0 [ARM64] + Allow execve() of 32-bit applications and setting of the + PER_LINUX32 personality on systems where only a strict + subset of the CPUs support 32-bit EL0. When this + parameter is present, the set of CPUs supporting 32-bit + EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 + and hot-unplug operations may be restricted. + amd_iommu= [HW,X86-64] Pass parameters to the AMD IOMMU driver in the system. Possible values are: diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 0a9bc7eff26e..77b2149c26b8 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1322,6 +1322,13 @@ const struct cpumask *system_32bit_el0_cpumask(void) return cpu_possible_mask; } +static int __init parse_32bit_el0_param(char *str) +{ + allow_mismatched_32bit_el0 = true; + return 0; +} +early_param("allow_mismatched_32bit_el0", parse_32bit_el0_param); + static ssize_t aarch32_el0_show(struct device *dev, struct device_attribute *attr, char *buf) { -- cgit v1.2.3