// SPDX-License-Identifier: GPL-2.0-only

#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/syscalls.h>
#include <linux/types.h>

#include <asm/cmpxchg.h>
#include <asm/cpufeature.h>
#include <asm/gcs.h>
#include <asm/page.h>

static unsigned long alloc_gcs(unsigned long addr, unsigned long size)
{
        int flags = MAP_ANONYMOUS | MAP_PRIVATE;
        struct mm_struct *mm = current->mm;
        unsigned long mapped_addr, unused;

        if (addr)
                flags |= MAP_FIXED_NOREPLACE;

        mmap_write_lock(mm);
        mapped_addr = do_mmap(NULL, addr, size, PROT_READ, flags,
                              VM_SHADOW_STACK | VM_WRITE, 0, &unused, NULL);
        mmap_write_unlock(mm);

        return mapped_addr;
}

static unsigned long gcs_size(unsigned long size)
{
        if (size)
                return PAGE_ALIGN(size);

        /* Allocate RLIMIT_STACK/2 with limits of PAGE_SIZE..2G */
        size = PAGE_ALIGN(min_t(unsigned long long,
                                rlimit(RLIMIT_STACK) / 2, SZ_2G));
        return max(PAGE_SIZE, size);
}

unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
                                     const struct kernel_clone_args *args)
{
        unsigned long addr, size;

        if (!system_supports_gcs())
                return 0;

        if (!task_gcs_el0_enabled(tsk))
                return 0;

        if ((args->flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM) {
                tsk->thread.gcspr_el0 = read_sysreg_s(SYS_GCSPR_EL0);
                return 0;
        }

        size = args->stack_size / 2;

        size = gcs_size(size);
        addr = alloc_gcs(0, size);
        if (IS_ERR_VALUE(addr))
                return addr;

        tsk->thread.gcs_base = addr;
        tsk->thread.gcs_size = size;
        tsk->thread.gcspr_el0 = addr + size - sizeof(u64);

        return addr;
}

SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
{
        unsigned long alloc_size;
        unsigned long __user *cap_ptr;
        unsigned long cap_val;
        int ret = 0;
        int cap_offset;

        if (!system_supports_gcs())
                return -EOPNOTSUPP;

        if (flags & ~(SHADOW_STACK_SET_TOKEN | SHADOW_STACK_SET_MARKER))
                return -EINVAL;

        if (!PAGE_ALIGNED(addr))
                return -EINVAL;

        if (size == 8 || !IS_ALIGNED(size, 8))
                return -EINVAL;

        /*
         * An overflow would result in attempting to write the restore token
         * to the wrong location. Not catastrophic, but just return the right
         * error code and block it.
         */
        alloc_size = PAGE_ALIGN(size);
        if (alloc_size < size)
                return -EOVERFLOW;

        addr = alloc_gcs(addr, alloc_size);
        if (IS_ERR_VALUE(addr))
                return addr;

        /*
         * Put a cap token at the end of the allocated region so it
         * can be switched to.
         */
        if (flags & SHADOW_STACK_SET_TOKEN) {
                /* Leave an extra empty frame as a top of stack marker? */
                if (flags & SHADOW_STACK_SET_MARKER)
                        cap_offset = 2;
                else
                        cap_offset = 1;

                cap_ptr = (unsigned long __user *)(addr + size -
                                                   (cap_offset * sizeof(unsigned long)));
                cap_val = GCS_CAP(cap_ptr);

                put_user_gcs(cap_val, cap_ptr, &ret);
                if (ret != 0) {
                        vm_munmap(addr, size);
                        return -EFAULT;
                }

                /*
                 * Ensure the new cap is ordered before standard
                 * memory accesses to the same location.
                 */
                gcsb_dsync();
        }

        return addr;
}

/*
 * Apply the GCS mode configured for the specified task to the
 * hardware.
 */
void gcs_set_el0_mode(struct task_struct *task)
{
        u64 gcscre0_el1 = GCSCRE0_EL1_nTR;

        if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE)
                gcscre0_el1 |= GCSCRE0_EL1_RVCHKEN | GCSCRE0_EL1_PCRSEL;

        if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_WRITE)
                gcscre0_el1 |= GCSCRE0_EL1_STREn;

        if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_PUSH)
                gcscre0_el1 |= GCSCRE0_EL1_PUSHMEn;

        write_sysreg_s(gcscre0_el1, SYS_GCSCRE0_EL1);
}

void gcs_free(struct task_struct *task)
{
        if (!system_supports_gcs())
                return;

        if (!task->mm || task->mm != current->mm)
                return;

        if (task->thread.gcs_base)
                vm_munmap(task->thread.gcs_base, task->thread.gcs_size);

        task->thread.gcspr_el0 = 0;
        task->thread.gcs_base = 0;
        task->thread.gcs_size = 0;
}

int arch_set_shadow_stack_status(struct task_struct *task, unsigned long arg)
{
        unsigned long gcs, size;
        int ret;

        if (!system_supports_gcs())
                return -EINVAL;

        if (is_compat_thread(task_thread_info(task)))
                return -EINVAL;

        /* Reject unknown flags */
        if (arg & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
                return -EINVAL;

        ret = gcs_check_locked(task, arg);
        if (ret != 0)
                return ret;

        /* If we are enabling GCS then make sure we have a stack */
        if (arg & PR_SHADOW_STACK_ENABLE &&
            !task_gcs_el0_enabled(task)) {
                /* Do not allow GCS to be reenabled */
                if (task->thread.gcs_base || task->thread.gcspr_el0)
                        return -EINVAL;

                if (task != current)
                        return -EBUSY;

                size = gcs_size(0);
                gcs = alloc_gcs(0, size);
                if (IS_ERR_VALUE(gcs))
                        return gcs;

                task->thread.gcspr_el0 = gcs + size - sizeof(u64);
                task->thread.gcs_base = gcs;
                task->thread.gcs_size = size;
                if (task == current)
                        write_sysreg_s(task->thread.gcspr_el0,
                                       SYS_GCSPR_EL0);
        }

        task->thread.gcs_el0_mode = arg;
        if (task == current)
                gcs_set_el0_mode(task);

        return 0;
}

int arch_get_shadow_stack_status(struct task_struct *task,
                                 unsigned long __user *arg)
{
        if (!system_supports_gcs())
                return -EINVAL;

        if (is_compat_thread(task_thread_info(task)))
                return -EINVAL;

        return put_user(task->thread.gcs_el0_mode, arg);
}

int arch_lock_shadow_stack_status(struct task_struct *task,
                                  unsigned long arg)
{
        if (!system_supports_gcs())
                return -EINVAL;

        if (is_compat_thread(task_thread_info(task)))
                return -EINVAL;

        /*
         * We support locking unknown bits so applications can prevent
         * any changes in a future proof manner.
         */
        task->thread.gcs_el0_locked |= arg;

        return 0;
}