vma.c

// 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/vdso_datastore.h>

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

static_assert(VDSO_NR_PAGES + VDSO_NR_VCLOCK_PAGES == __VDSO_PAGES);

unsigned int vclocks_used __read_mostly;

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

int __init init_vdso_image(const struct vdso_image *image)
{
	BUILD_BUG_ON(VDSO_CLOCKMODE_MAX >= 32);
	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));

	return 0;
}

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)
{
	struct pt_regs *regs = current_pt_regs();
	unsigned long ipoffset = regs->ip -
		(unsigned long)current->mm->context.vdso;

	if (ipoffset < image->size)
		regs->ip = new_vma->vm_start + ipoffset;
}

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;
}

static vm_fault_t vvar_vclock_fault(const struct vm_special_mapping *sm,
				    struct vm_area_struct *vma, struct vm_fault *vmf)
{
	switch (vmf->pgoff) {
#ifdef CONFIG_PARAVIRT_CLOCK
	case VDSO_PAGE_PVCLOCK_OFFSET:
	{
		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));
		break;
	}
#endif /* CONFIG_PARAVIRT_CLOCK */
#ifdef CONFIG_HYPERV_TIMER
	case VDSO_PAGE_HVCLOCK_OFFSET:
	{
		unsigned long pfn = hv_get_tsc_pfn();
		if (pfn && vclock_was_used(VDSO_CLOCKMODE_HVCLOCK))
			return vmf_insert_pfn(vma, vmf->address, pfn);
		break;
	}
#endif /* CONFIG_HYPERV_TIMER */
	}

	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_vclock_mapping = {
	.name = "[vvar_vclock]",
	.fault = vvar_vclock_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 + __VDSO_PAGES * PAGE_SIZE, 0, 0);
	if (IS_ERR_VALUE(addr)) {
		ret = addr;
		goto up_fail;
	}

	text_start = addr + __VDSO_PAGES * PAGE_SIZE;

	/*
	 * 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|
				       VM_SEALED_SYSMAP,
				       &vdso_mapping);

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

	vma = vdso_install_vvar_mapping(mm, addr);
	if (IS_ERR(vma)) {
		ret = PTR_ERR(vma);
		do_munmap(mm, text_start, image->size, NULL);
		goto up_fail;
	}

	vma = _install_special_mapping(mm,
				       VDSO_VCLOCK_PAGES_START(addr),
				       VDSO_NR_VCLOCK_PAGES * PAGE_SIZE,
				       VM_READ|VM_MAYREAD|VM_IO|VM_DONTDUMP|
				       VM_PFNMAP|VM_SEALED_SYSMAP,
				       &vvar_vclock_mapping);

	if (IS_ERR(vma)) {
		ret = PTR_ERR(vma);
		do_munmap(mm, text_start, image->size, NULL);
		do_munmap(mm, addr, image->size, NULL);
		goto up_fail;
	}

	current->mm->context.vdso = (void __user *)text_start;
	current->mm->context.vdso_image = image;

up_fail:
	mmap_write_unlock(mm);
	return ret;
}

int map_vdso_once(const struct vdso_image *image, unsigned long addr)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	VMA_ITERATOR(vmi, mm, 0);

	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_each_vma(vmi, vma) {
		if (vma_is_special_mapping(vma, &vdso_mapping) ||
				vma_is_special_mapping(vma, &vdso_vvar_mapping) ||
				vma_is_special_mapping(vma, &vvar_vclock_mapping)) {
			mmap_write_unlock(mm);
			return -EEXIST;
		}
	}
	mmap_write_unlock(mm);

	return map_vdso(image, addr);
}

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

	return map_vdso(&vdso32_image, 0);
}

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

		return map_vdso(&vdso64_image, 0);
	}

	return load_vdso32();
}

#ifdef CONFIG_COMPAT
int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
				       int uses_interp, bool x32)
{
	if (IS_ENABLED(CONFIG_X86_X32_ABI) && x32) {
		if (!vdso64_enabled)
			return 0;
		return map_vdso(&vdsox32_image, 0);
	}

	if (IS_ENABLED(CONFIG_IA32_EMULATION))
		return load_vdso32();

	return 0;
}
#endif

bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
{
	const struct vdso_image *image = current->mm->context.vdso_image;
	unsigned long vdso = (unsigned long) current->mm->context.vdso;

	if (in_ia32_syscall() && image == &vdso32_image) {
		if (regs->ip == vdso + image->sym_vdso32_sigreturn_landing_pad ||
		    regs->ip == vdso + image->sym_vdso32_rt_sigreturn_landing_pad)
			return true;
	}
	return false;
}

#ifdef CONFIG_X86_64
static __init int vdso_setup(char *s)
{
	vdso64_enabled = simple_strtoul(s, NULL, 0);
	return 1;
}
__setup("vdso=", vdso_setup);
#endif /* CONFIG_X86_64 */