// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 2007 Andi Kleen, SUSE Labs.
 *
 * This contains most of the x86 vDSO kernel-side code.
 */
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/random.h>
#include <linux/elf.h>
#include <linux/cpu.h>
#include <linux/ptrace.h>
#include <linux/time_namespace.h>

#include <asm/pvclock.h>
#include <asm/vgtod.h>
#include <asm/proto.h>
#include <asm/vdso.h>
#include <asm/vvar.h>
#include <asm/tlb.h>
#include <asm/page.h>
#include <asm/desc.h>
#include <asm/cpufeature.h>
#include <clocksource/hyperv_timer.h>

#undef _ASM_X86_VVAR_H
#define EMIT_VVAR(name, offset) \
        const size_t name ## _offset = offset;
#include <asm/vvar.h>

struct vdso_data *arch_get_vdso_data(void *vvar_page)
{
        return (struct vdso_data *)(vvar_page + _vdso_data_offset);
}
#undef EMIT_VVAR

unsigned int vclocks_used __read_mostly;

#if defined(CONFIG_X86_64)
unsigned int __read_mostly vdso64_enabled = 1;
#endif

void __init init_vdso_image(const struct vdso_image *image)
{
        BUG_ON(image->size % PAGE_SIZE != 0);

        apply_alternatives((struct alt_instr *)(image->data + image->alt),
                           (struct alt_instr *)(image->data + image->alt +
                                                image->alt_len));
}

static const struct vm_special_mapping vvar_mapping;
struct linux_binprm;

static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
                      struct vm_area_struct *vma, struct vm_fault *vmf)
{
        const struct vdso_image *image = vma->vm_mm->context.vdso_image;

        if (!image || (vmf->pgoff << PAGE_SHIFT) >= image->size)
                return VM_FAULT_SIGBUS;

        vmf->page = virt_to_page(image->data + (vmf->pgoff << PAGE_SHIFT));
        get_page(vmf->page);
        return 0;
}

static void vdso_fix_landing(const struct vdso_image *image,
                struct vm_area_struct *new_vma)
{
#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
        if (in_ia32_syscall() && image == &vdso_image_32) {
                struct pt_regs *regs = current_pt_regs();
                unsigned long vdso_land = image->sym_int80_landing_pad;
                unsigned long old_land_addr = vdso_land +
                        (unsigned long)current->mm->context.vdso;

                /* Fixing userspace landing - look at do_fast_syscall_32 */
                if (regs->ip == old_land_addr)
                        regs->ip = new_vma->vm_start + vdso_land;
        }
#endif
}

static int vdso_mremap(const struct vm_special_mapping *sm,
                struct vm_area_struct *new_vma)
{
        const struct vdso_image *image = current->mm->context.vdso_image;

        vdso_fix_landing(image, new_vma);
        current->mm->context.vdso = (void __user *)new_vma->vm_start;

        return 0;
}

#ifdef CONFIG_TIME_NS
static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
{
        if (likely(vma->vm_mm == current->mm))
                return current->nsproxy->time_ns->vvar_page;

        /*
         * VM_PFNMAP | VM_IO protect .fault() handler from being called
         * through interfaces like /proc/$pid/mem or
         * process_vm_{readv,writev}() as long as there's no .access()
         * in special_mapping_vmops().
         * For more details check_vma_flags() and __access_remote_vm()
         */

        WARN(1, "vvar_page accessed remotely");

        return NULL;
}

/*
 * The vvar page layout depends on whether a task belongs to the root or
 * non-root time namespace. Whenever a task changes its namespace, the VVAR
 * page tables are cleared and then they will re-faulted with a
 * corresponding layout.
 * See also the comment near timens_setup_vdso_data() for details.
 */
int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
{
        struct mm_struct *mm = task->mm;
        struct vm_area_struct *vma;

        mmap_read_lock(mm);

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                unsigned long size = vma->vm_end - vma->vm_start;

                if (vma_is_special_mapping(vma, &vvar_mapping))
                        zap_page_range(vma, vma->vm_start, size);
        }

        mmap_read_unlock(mm);
        return 0;
}
#else
static inline struct page *find_timens_vvar_page(struct vm_area_struct *vma)
{
        return NULL;
}
#endif

static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
                      struct vm_area_struct *vma, struct vm_fault *vmf)
{
        const struct vdso_image *image = vma->vm_mm->context.vdso_image;
        unsigned long pfn;
        long sym_offset;

        if (!image)
                return VM_FAULT_SIGBUS;

        sym_offset = (long)(vmf->pgoff << PAGE_SHIFT) +
                image->sym_vvar_start;

        /*
         * Sanity check: a symbol offset of zero means that the page
         * does not exist for this vdso image, not that the page is at
         * offset zero relative to the text mapping.  This should be
         * impossible here, because sym_offset should only be zero for
         * the page past the end of the vvar mapping.
         */
        if (sym_offset == 0)
                return VM_FAULT_SIGBUS;

        if (sym_offset == image->sym_vvar_page) {
                struct page *timens_page = find_timens_vvar_page(vma);

                pfn = __pa_symbol(&__vvar_page) >> PAGE_SHIFT;

                /*
                 * If a task belongs to a time namespace then a namespace
                 * specific VVAR is mapped with the sym_vvar_page offset and
                 * the real VVAR page is mapped with the sym_timens_page
                 * offset.
                 * See also the comment near timens_setup_vdso_data().
                 */
                if (timens_page) {
                        unsigned long addr;
                        vm_fault_t err;

                        /*
                         * Optimization: inside time namespace pre-fault
                         * VVAR page too. As on timens page there are only
                         * offsets for clocks on VVAR, it'll be faulted
                         * shortly by VDSO code.
                         */
                        addr = vmf->address + (image->sym_timens_page - sym_offset);
                        err = vmf_insert_pfn(vma, addr, pfn);
                        if (unlikely(err & VM_FAULT_ERROR))
                                return err;

                        pfn = page_to_pfn(timens_page);
                }

                return vmf_insert_pfn(vma, vmf->address, pfn);
        } else if (sym_offset == image->sym_pvclock_page) {
                struct pvclock_vsyscall_time_info *pvti =
                        pvclock_get_pvti_cpu0_va();
                if (pvti && vclock_was_used(VDSO_CLOCKMODE_PVCLOCK)) {
                        return vmf_insert_pfn_prot(vma, vmf->address,
                                        __pa(pvti) >> PAGE_SHIFT,
                                        pgprot_decrypted(vma->vm_page_prot));
                }
        } else if (sym_offset == image->sym_hvclock_page) {
                struct ms_hyperv_tsc_page *tsc_pg = hv_get_tsc_page();

                if (tsc_pg && vclock_was_used(VDSO_CLOCKMODE_HVCLOCK))
                        return vmf_insert_pfn(vma, vmf->address,
                                        virt_to_phys(tsc_pg) >> PAGE_SHIFT);
        } else if (sym_offset == image->sym_timens_page) {
                struct page *timens_page = find_timens_vvar_page(vma);

                if (!timens_page)
                        return VM_FAULT_SIGBUS;

                pfn = __pa_symbol(&__vvar_page) >> PAGE_SHIFT;
                return vmf_insert_pfn(vma, vmf->address, pfn);
        }

        return VM_FAULT_SIGBUS;
}

static const struct vm_special_mapping vdso_mapping = {
        .name = "[vdso]",
        .fault = vdso_fault,
        .mremap = vdso_mremap,
};
static const struct vm_special_mapping vvar_mapping = {
        .name = "[vvar]",
        .fault = vvar_fault,
};

/*
 * Add vdso and vvar mappings to current process.
 * @image          - blob to map
 * @addr           - request a specific address (zero to map at free addr)
 */
static int map_vdso(const struct vdso_image *image, unsigned long addr)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long text_start;
        int ret = 0;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        addr = get_unmapped_area(NULL, addr,
                                 image->size - image->sym_vvar_start, 0, 0);
        if (IS_ERR_VALUE(addr)) {
                ret = addr;
                goto up_fail;
        }

        text_start = addr - image->sym_vvar_start;

        /*
         * MAYWRITE to allow gdb to COW and set breakpoints
         */
        vma = _install_special_mapping(mm,
                                       text_start,
                                       image->size,
                                       VM_READ|VM_EXEC|
                                       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
                                       &vdso_mapping);

        if (IS_ERR(vma)) {
                ret = PTR_ERR(vma);
                goto up_fail;
        }

        vma = _install_special_mapping(mm,
                                       addr,
                                       -image->sym_vvar_start,
                                       VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
                                       VM_PFNMAP,
                                       &vvar_mapping);

        if (IS_ERR(vma)) {
                ret = PTR_ERR(vma);
                do_munmap(mm, text_start, image->size, NULL);
        } else {
                current->mm->context.vdso = (void __user *)text_start;
                current->mm->context.vdso_image = image;
        }

up_fail:
        mmap_write_unlock(mm);
        return ret;
}

#ifdef CONFIG_X86_64
/*
 * Put the vdso above the (randomized) stack with another randomized
 * offset.  This way there is no hole in the middle of address space.
 * To save memory make sure it is still in the same PTE as the stack
 * top.  This doesn't give that many random bits.
 *
 * Note that this algorithm is imperfect: the distribution of the vdso
 * start address within a PMD is biased toward the end.
 *
 * Only used for the 64-bit and x32 vdsos.
 */
static unsigned long vdso_addr(unsigned long start, unsigned len)
{
        unsigned long addr, end;
        unsigned offset;

        /*
         * Round up the start address.  It can start out unaligned as a result
         * of stack start randomization.
         */
        start = PAGE_ALIGN(start);

        /* Round the lowest possible end address up to a PMD boundary. */
        end = (start + len + PMD_SIZE - 1) & PMD_MASK;
        if (end >= TASK_SIZE_MAX)
                end = TASK_SIZE_MAX;
        end -= len;

        if (end > start) {
                offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
                addr = start + (offset << PAGE_SHIFT);
        } else {
                addr = start;
        }

        /*
         * Forcibly align the final address in case we have a hardware
         * issue that requires alignment for performance reasons.
         */
        addr = align_vdso_addr(addr);

        return addr;
}

static int map_vdso_randomized(const struct vdso_image *image)
{
        unsigned long addr = vdso_addr(current->mm->start_stack, image->size-image->sym_vvar_start);

        return map_vdso(image, addr);
}
#endif

int map_vdso_once(const struct vdso_image *image, unsigned long addr)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;

        mmap_write_lock(mm);
        /*
         * Check if we have already mapped vdso blob - fail to prevent
         * abusing from userspace install_special_mapping, which may
         * not do accounting and rlimit right.
         * We could search vma near context.vdso, but it's a slowpath,
         * so let's explicitly check all VMAs to be completely sure.
         */
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (vma_is_special_mapping(vma, &vdso_mapping) ||
                                vma_is_special_mapping(vma, &vvar_mapping)) {
                        mmap_write_unlock(mm);
                        return -EEXIST;
                }
        }
        mmap_write_unlock(mm);

        return map_vdso(image, addr);
}

#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
static int load_vdso32(void)
{
        if (vdso32_enabled != 1)  /* Other values all mean "disabled" */
                return 0;

        return map_vdso(&vdso_image_32, 0);
}
#endif

#ifdef CONFIG_X86_64
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
        if (!vdso64_enabled)
                return 0;

        return map_vdso_randomized(&vdso_image_64);
}

#ifdef CONFIG_COMPAT
int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
                                       int uses_interp, bool x32)
{
#ifdef CONFIG_X86_X32_ABI
        if (x32) {
                if (!vdso64_enabled)
                        return 0;
                return map_vdso_randomized(&vdso_image_x32);
        }
#endif
#ifdef CONFIG_IA32_EMULATION
        return load_vdso32();
#else
        return 0;
#endif
}
#endif
#else
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
        return load_vdso32();
}
#endif

bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
{
#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
        const struct vdso_image *image = current->mm->context.vdso_image;
        unsigned long vdso = (unsigned long) current->mm->context.vdso;

        if (in_ia32_syscall() && image == &vdso_image_32) {
                if (regs->ip == vdso + image->sym_vdso32_sigreturn_landing_pad ||
                    regs->ip == vdso + image->sym_vdso32_rt_sigreturn_landing_pad)
                        return true;
        }
#endif
        return false;
}

#ifdef CONFIG_X86_64
static __init int vdso_setup(char *s)
{
        vdso64_enabled = simple_strtoul(s, NULL, 0);
        return 0;
}
__setup("vdso=", vdso_setup);

static int __init init_vdso(void)
{
        BUILD_BUG_ON(VDSO_CLOCKMODE_MAX >= 32);

        init_vdso_image(&vdso_image_64);

#ifdef CONFIG_X86_X32_ABI
        init_vdso_image(&vdso_image_x32);
#endif

        return 0;
}
subsys_initcall(init_vdso);
#endif /* CONFIG_X86_64 */