linux/arch/s390/mm/fault.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  S390 version
 *    Copyright IBM Corp. 1999
 *    Author(s): Hartmut Penner (hp@de.ibm.com)
 *               Ulrich Weigand (uweigand@de.ibm.com)
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1995  Linus Torvalds
 */

#include <linux/kernel_stat.h>
#include <linux/perf_event.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/compat.h>
#include <linux/smp.h>
#include <linux/kdebug.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/extable.h>
#include <linux/hardirq.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/hugetlb.h>
#include <linux/kfence.h>
#include <asm/asm-extable.h>
#include <asm/asm-offsets.h>
#include <asm/diag.h>
#include <asm/gmap.h>
#include <asm/irq.h>
#include <asm/mmu_context.h>
#include <asm/facility.h>
#include <asm/uv.h>
#include "../kernel/entry.h"

#define __FAIL_ADDR_MASK -4096L

/*
 * Allocate private vm_fault_reason from top.  Please make sure it won't
 * collide with vm_fault_reason.
 */
#define VM_FAULT_BADCONTEXT	((__force vm_fault_t)0x80000000)
#define VM_FAULT_BADMAP		((__force vm_fault_t)0x40000000)
#define VM_FAULT_BADACCESS	((__force vm_fault_t)0x20000000)
#define VM_FAULT_SIGNAL		((__force vm_fault_t)0x10000000)
#define VM_FAULT_PFAULT		((__force vm_fault_t)0x8000000)

enum fault_type {
	KERNEL_FAULT,
	USER_FAULT,
	GMAP_FAULT,
};

static unsigned long store_indication __read_mostly;

static int __init fault_init(void)
{
	if (test_facility(75))
		store_indication = 0xc00;
	return 0;
}
early_initcall(fault_init);

/*
 * Find out which address space caused the exception.
 */
static enum fault_type get_fault_type(struct pt_regs *regs)
{
	unsigned long trans_exc_code;

	trans_exc_code = regs->int_parm_long & 3;
	if (likely(trans_exc_code == 0)) {
		/* primary space exception */
		if (user_mode(regs))
			return USER_FAULT;
		if (!IS_ENABLED(CONFIG_PGSTE))
			return KERNEL_FAULT;
		if (test_pt_regs_flag(regs, PIF_GUEST_FAULT))
			return GMAP_FAULT;
		return KERNEL_FAULT;
	}
	if (trans_exc_code == 2)
		return USER_FAULT;
	if (trans_exc_code == 1) {
		/* access register mode, not used in the kernel */
		return USER_FAULT;
	}
	/* home space exception -> access via kernel ASCE */
	return KERNEL_FAULT;
}

static unsigned long get_fault_address(struct pt_regs *regs)
{
	unsigned long trans_exc_code = regs->int_parm_long;

	return trans_exc_code & __FAIL_ADDR_MASK;
}

static bool fault_is_write(struct pt_regs *regs)
{
	unsigned long trans_exc_code = regs->int_parm_long;

	return (trans_exc_code & store_indication) == 0x400;
}

static int bad_address(void *p)
{
	unsigned long dummy;

	return get_kernel_nofault(dummy, (unsigned long *)p);
}

static void dump_pagetable(unsigned long asce, unsigned long address)
{
	unsigned long *table = __va(asce & _ASCE_ORIGIN);

	pr_alert("AS:%016lx ", asce);
	switch (asce & _ASCE_TYPE_MASK) {
	case _ASCE_TYPE_REGION1:
		table += (address & _REGION1_INDEX) >> _REGION1_SHIFT;
		if (bad_address(table))
			goto bad;
		pr_cont("R1:%016lx ", *table);
		if (*table & _REGION_ENTRY_INVALID)
			goto out;
		table = __va(*table & _REGION_ENTRY_ORIGIN);
		fallthrough;
	case _ASCE_TYPE_REGION2:
		table += (address & _REGION2_INDEX) >> _REGION2_SHIFT;
		if (bad_address(table))
			goto bad;
		pr_cont("R2:%016lx ", *table);
		if (*table & _REGION_ENTRY_INVALID)
			goto out;
		table = __va(*table & _REGION_ENTRY_ORIGIN);
		fallthrough;
	case _ASCE_TYPE_REGION3:
		table += (address & _REGION3_INDEX) >> _REGION3_SHIFT;
		if (bad_address(table))
			goto bad;
		pr_cont("R3:%016lx ", *table);
		if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
			goto out;
		table = __va(*table & _REGION_ENTRY_ORIGIN);
		fallthrough;
	case _ASCE_TYPE_SEGMENT:
		table += (address & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
		if (bad_address(table))
			goto bad;
		pr_cont("S:%016lx ", *table);
		if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
			goto out;
		table = __va(*table & _SEGMENT_ENTRY_ORIGIN);
	}
	table += (address & _PAGE_INDEX) >> _PAGE_SHIFT;
	if (bad_address(table))
		goto bad;
	pr_cont("P:%016lx ", *table);
out:
	pr_cont("\n");
	return;
bad:
	pr_cont("BAD\n");
}

static void dump_fault_info(struct pt_regs *regs)
{
	unsigned long asce;

	pr_alert("Failing address: %016lx TEID: %016lx\n",
		 regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
	pr_alert("Fault in ");
	switch (regs->int_parm_long & 3) {
	case 3:
		pr_cont("home space ");
		break;
	case 2:
		pr_cont("secondary space ");
		break;
	case 1:
		pr_cont("access register ");
		break;
	case 0:
		pr_cont("primary space ");
		break;
	}
	pr_cont("mode while using ");
	switch (get_fault_type(regs)) {
	case USER_FAULT:
		asce = S390_lowcore.user_asce;
		pr_cont("user ");
		break;
	case GMAP_FAULT:
		asce = ((struct gmap *) S390_lowcore.gmap)->asce;
		pr_cont("gmap ");
		break;
	case KERNEL_FAULT:
		asce = S390_lowcore.kernel_asce;
		pr_cont("kernel ");
		break;
	default:
		unreachable();
	}
	pr_cont("ASCE.\n");
	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
}

int show_unhandled_signals = 1;

void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
{
	if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
		return;
	if (!unhandled_signal(current, signr))
		return;
	if (!printk_ratelimit())
		return;
	printk(KERN_ALERT "User process fault: interruption code %04x ilc:%d ",
	       regs->int_code & 0xffff, regs->int_code >> 17);
	print_vma_addr(KERN_CONT "in ", regs->psw.addr);
	printk(KERN_CONT "\n");
	if (is_mm_fault)
		dump_fault_info(regs);
	show_regs(regs);
}

/*
 * Send SIGSEGV to task.  This is an external routine
 * to keep the stack usage of do_page_fault small.
 */
static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
{
	report_user_fault(regs, SIGSEGV, 1);
	force_sig_fault(SIGSEGV, si_code,
			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK));
}

static noinline void do_no_context(struct pt_regs *regs, vm_fault_t fault)
{
	enum fault_type fault_type;
	unsigned long address;
	bool is_write;

	if (fixup_exception(regs))
		return;
	fault_type = get_fault_type(regs);
	if ((fault_type == KERNEL_FAULT) && (fault == VM_FAULT_BADCONTEXT)) {
		address = get_fault_address(regs);
		is_write = fault_is_write(regs);
		if (kfence_handle_page_fault(address, is_write, regs))
			return;
	}
	/*
	 * Oops. The kernel tried to access some bad page. We'll have to
	 * terminate things with extreme prejudice.
	 */
	if (fault_type == KERNEL_FAULT)
		printk(KERN_ALERT "Unable to handle kernel pointer dereference"
		       " in virtual kernel address space\n");
	else
		printk(KERN_ALERT "Unable to handle kernel paging request"
		       " in virtual user address space\n");
	dump_fault_info(regs);
	die(regs, "Oops");
}

static noinline void do_low_address(struct pt_regs *regs)
{
	/* Low-address protection hit in kernel mode means
	   NULL pointer write access in kernel mode.  */
	if (regs->psw.mask & PSW_MASK_PSTATE) {
		/* Low-address protection hit in user mode 'cannot happen'. */
		die (regs, "Low-address protection");
	}

	do_no_context(regs, VM_FAULT_BADACCESS);
}

static noinline void do_sigbus(struct pt_regs *regs)
{
	/*
	 * Send a sigbus, regardless of whether we were in kernel
	 * or user mode.
	 */
	force_sig_fault(SIGBUS, BUS_ADRERR,
			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK));
}

static noinline void do_fault_error(struct pt_regs *regs, vm_fault_t fault)
{
	int si_code;

	switch (fault) {
	case VM_FAULT_BADACCESS:
	case VM_FAULT_BADMAP:
		/* Bad memory access. Check if it is kernel or user space. */
		if (user_mode(regs)) {
			/* User mode accesses just cause a SIGSEGV */
			si_code = (fault == VM_FAULT_BADMAP) ?
				SEGV_MAPERR : SEGV_ACCERR;
			do_sigsegv(regs, si_code);
			break;
		}
		fallthrough;
	case VM_FAULT_BADCONTEXT:
	case VM_FAULT_PFAULT:
		do_no_context(regs, fault);
		break;
	case VM_FAULT_SIGNAL:
		if (!user_mode(regs))
			do_no_context(regs, fault);
		break;
	default: /* fault & VM_FAULT_ERROR */
		if (fault & VM_FAULT_OOM) {
			if (!user_mode(regs))
				do_no_context(regs, fault);
			else
				pagefault_out_of_memory();
		} else if (fault & VM_FAULT_SIGSEGV) {
			/* Kernel mode? Handle exceptions or die */
			if (!user_mode(regs))
				do_no_context(regs, fault);
			else
				do_sigsegv(regs, SEGV_MAPERR);
		} else if (fault & VM_FAULT_SIGBUS) {
			/* Kernel mode? Handle exceptions or die */
			if (!user_mode(regs))
				do_no_context(regs, fault);
			else
				do_sigbus(regs);
		} else
			BUG();
		break;
	}
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * interruption code (int_code):
 *   04       Protection           ->  Write-Protection  (suppression)
 *   10       Segment translation  ->  Not present       (nullification)
 *   11       Page translation     ->  Not present       (nullification)
 *   3b       Region third trans.  ->  Not present       (nullification)
 */
static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
{
	struct gmap *gmap;
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
	enum fault_type type;
	unsigned long address;
	unsigned int flags;
	vm_fault_t fault;
	bool is_write;

	tsk = current;
	/*
	 * The instruction that caused the program check has
	 * been nullified. Don't signal single step via SIGTRAP.
	 */
	clear_thread_flag(TIF_PER_TRAP);

	if (kprobe_page_fault(regs, 14))
		return 0;

	mm = tsk->mm;
	address = get_fault_address(regs);
	is_write = fault_is_write(regs);

	/*
	 * Verify that the fault happened in user space, that
	 * we are not in an interrupt and that there is a 
	 * user context.
	 */
	fault = VM_FAULT_BADCONTEXT;
	type = get_fault_type(regs);
	switch (type) {
	case KERNEL_FAULT:
		goto out;
	case USER_FAULT:
	case GMAP_FAULT:
		if (faulthandler_disabled() || !mm)
			goto out;
		break;
	}

	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
	flags = FAULT_FLAG_DEFAULT;
	if (user_mode(regs))
		flags |= FAULT_FLAG_USER;
	if (is_write)
		access = VM_WRITE;
	if (access == VM_WRITE)
		flags |= FAULT_FLAG_WRITE;
	if (!(flags & FAULT_FLAG_USER))
		goto lock_mmap;
	vma = lock_vma_under_rcu(mm, address);
	if (!vma)
		goto lock_mmap;
	if (!(vma->vm_flags & access)) {
		vma_end_read(vma);
		goto lock_mmap;
	}
	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
		vma_end_read(vma);
	if (!(fault & VM_FAULT_RETRY)) {
		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
		if (likely(!(fault & VM_FAULT_ERROR)))
			fault = 0;
		goto out;
	}
	count_vm_vma_lock_event(VMA_LOCK_RETRY);
	/* Quick path to respond to signals */
	if (fault_signal_pending(fault, regs)) {
		fault = VM_FAULT_SIGNAL;
		goto out;
	}
lock_mmap:
	mmap_read_lock(mm);

	gmap = NULL;
	if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
		gmap = (struct gmap *) S390_lowcore.gmap;
		current->thread.gmap_addr = address;
		current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
		current->thread.gmap_int_code = regs->int_code & 0xffff;
		address = __gmap_translate(gmap, address);
		if (address == -EFAULT) {
			fault = VM_FAULT_BADMAP;
			goto out_up;
		}
		if (gmap->pfault_enabled)
			flags |= FAULT_FLAG_RETRY_NOWAIT;
	}

retry:
	fault = VM_FAULT_BADMAP;
	vma = find_vma(mm, address);
	if (!vma)
		goto out_up;

	if (unlikely(vma->vm_start > address)) {
		if (!(vma->vm_flags & VM_GROWSDOWN))
			goto out_up;
		vma = expand_stack(mm, address);
		if (!vma)
			goto out;
	}

	/*
	 * Ok, we have a good vm_area for this memory access, so
	 * we can handle it..
	 */
	fault = VM_FAULT_BADACCESS;
	if (unlikely(!(vma->vm_flags & access)))
		goto out_up;

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */
	fault = handle_mm_fault(vma, address, flags, regs);
	if (fault_signal_pending(fault, regs)) {
		fault = VM_FAULT_SIGNAL;
		if (flags & FAULT_FLAG_RETRY_NOWAIT)
			goto out_up;
		goto out;
	}

	/* The fault is fully completed (including releasing mmap lock) */
	if (fault & VM_FAULT_COMPLETED) {
		if (gmap) {
			mmap_read_lock(mm);
			goto out_gmap;
		}
		fault = 0;
		goto out;
	}

	if (unlikely(fault & VM_FAULT_ERROR))
		goto out_up;

	if (fault & VM_FAULT_RETRY) {
		if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
			(flags & FAULT_FLAG_RETRY_NOWAIT)) {
			/*
			 * FAULT_FLAG_RETRY_NOWAIT has been set, mmap_lock has
			 * not been released
			 */
			current->thread.gmap_pfault = 1;
			fault = VM_FAULT_PFAULT;
			goto out_up;
		}
		flags &= ~FAULT_FLAG_RETRY_NOWAIT;
		flags |= FAULT_FLAG_TRIED;
		mmap_read_lock(mm);
		goto retry;
	}
out_gmap:
	if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
		address =  __gmap_link(gmap, current->thread.gmap_addr,
				       address);
		if (address == -EFAULT) {
			fault = VM_FAULT_BADMAP;
			goto out_up;
		}
		if (address == -ENOMEM) {
			fault = VM_FAULT_OOM;
			goto out_up;
		}
	}
	fault = 0;
out_up:
	mmap_read_unlock(mm);
out:
	return fault;
}

void do_protection_exception(struct pt_regs *regs)
{
	unsigned long trans_exc_code;
	int access;
	vm_fault_t fault;

	trans_exc_code = regs->int_parm_long;
	/*
	 * Protection exceptions are suppressing, decrement psw address.
	 * The exception to this rule are aborted transactions, for these
	 * the PSW already points to the correct location.
	 */
	if (!(regs->int_code & 0x200))
		regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
	/*
	 * Check for low-address protection.  This needs to be treated
	 * as a special case because the translation exception code
	 * field is not guaranteed to contain valid data in this case.
	 */
	if (unlikely(!(trans_exc_code & 4))) {
		do_low_address(regs);
		return;
	}
	if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
		regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) |
					(regs->psw.addr & PAGE_MASK);
		access = VM_EXEC;
		fault = VM_FAULT_BADACCESS;
	} else {
		access = VM_WRITE;
		fault = do_exception(regs, access);
	}
	if (unlikely(fault))
		do_fault_error(regs, fault);
}
NOKPROBE_SYMBOL(do_protection_exception);

void do_dat_exception(struct pt_regs *regs)
{
	int access;
	vm_fault_t fault;

	access = VM_ACCESS_FLAGS;
	fault = do_exception(regs, access);
	if (unlikely(fault))
		do_fault_error(regs, fault);
}
NOKPROBE_SYMBOL(do_dat_exception);

#if IS_ENABLED(CONFIG_PGSTE)

void do_secure_storage_access(struct pt_regs *regs)
{
	unsigned long addr = regs->int_parm_long & __FAIL_ADDR_MASK;
	struct vm_area_struct *vma;
	struct mm_struct *mm;
	struct page *page;
	struct gmap *gmap;
	int rc;

	/*
	 * bit 61 tells us if the address is valid, if it's not we
	 * have a major problem and should stop the kernel or send a
	 * SIGSEGV to the process. Unfortunately bit 61 is not
	 * reliable without the misc UV feature so we need to check
	 * for that as well.
	 */
	if (uv_has_feature(BIT_UV_FEAT_MISC) &&
	    !test_bit_inv(61, &regs->int_parm_long)) {
		/*
		 * When this happens, userspace did something that it
		 * was not supposed to do, e.g. branching into secure
		 * memory. Trigger a segmentation fault.
		 */
		if (user_mode(regs)) {
			send_sig(SIGSEGV, current, 0);
			return;
		}

		/*
		 * The kernel should never run into this case and we
		 * have no way out of this situation.
		 */
		panic("Unexpected PGM 0x3d with TEID bit 61=0");
	}

	switch (get_fault_type(regs)) {
	case GMAP_FAULT:
		mm = current->mm;
		gmap = (struct gmap *)S390_lowcore.gmap;
		mmap_read_lock(mm);
		addr = __gmap_translate(gmap, addr);
		mmap_read_unlock(mm);
		if (IS_ERR_VALUE(addr)) {
			do_fault_error(regs, VM_FAULT_BADMAP);
			break;
		}
		fallthrough;
	case USER_FAULT:
		mm = current->mm;
		mmap_read_lock(mm);
		vma = find_vma(mm, addr);
		if (!vma) {
			mmap_read_unlock(mm);
			do_fault_error(regs, VM_FAULT_BADMAP);
			break;
		}
		page = follow_page(vma, addr, FOLL_WRITE | FOLL_GET);
		if (IS_ERR_OR_NULL(page)) {
			mmap_read_unlock(mm);
			break;
		}
		if (arch_make_page_accessible(page))
			send_sig(SIGSEGV, current, 0);
		put_page(page);
		mmap_read_unlock(mm);
		break;
	case KERNEL_FAULT:
		page = phys_to_page(addr);
		if (unlikely(!try_get_page(page)))
			break;
		rc = arch_make_page_accessible(page);
		put_page(page);
		if (rc)
			BUG();
		break;
	default:
		do_fault_error(regs, VM_FAULT_BADMAP);
		WARN_ON_ONCE(1);
	}
}
NOKPROBE_SYMBOL(do_secure_storage_access);

void do_non_secure_storage_access(struct pt_regs *regs)
{
	unsigned long gaddr = regs->int_parm_long & __FAIL_ADDR_MASK;
	struct gmap *gmap = (struct gmap *)S390_lowcore.gmap;

	if (get_fault_type(regs) != GMAP_FAULT) {
		do_fault_error(regs, VM_FAULT_BADMAP);
		WARN_ON_ONCE(1);
		return;
	}

	if (gmap_convert_to_secure(gmap, gaddr) == -EINVAL)
		send_sig(SIGSEGV, current, 0);
}
NOKPROBE_SYMBOL(do_non_secure_storage_access);

void do_secure_storage_violation(struct pt_regs *regs)
{
	unsigned long gaddr = regs->int_parm_long & __FAIL_ADDR_MASK;
	struct gmap *gmap = (struct gmap *)S390_lowcore.gmap;

	/*
	 * If the VM has been rebooted, its address space might still contain
	 * secure pages from the previous boot.
	 * Clear the page so it can be reused.
	 */
	if (!gmap_destroy_page(gmap, gaddr))
		return;
	/*
	 * Either KVM messed up the secure guest mapping or the same
	 * page is mapped into multiple secure guests.
	 *
	 * This exception is only triggered when a guest 2 is running
	 * and can therefore never occur in kernel context.
	 */
	printk_ratelimited(KERN_WARNING
			   "Secure storage violation in task: %s, pid %d\n",
			   current->comm, current->pid);
	send_sig(SIGSEGV, current, 0);
}

#endif /* CONFIG_PGSTE */