fault.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
 *
 * Derived from MIPS:
 * Copyright (C) 1995 - 2000 by Ralf Baechle
 */
#include <linux/context_tracking.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/entry-common.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/ratelimit.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/kdebug.h>
#include <linux/perf_event.h>
#include <linux/uaccess.h>
#include <linux/kfence.h>

#include <asm/branch.h>
#include <asm/exception.h>
#include <asm/mmu_context.h>
#include <asm/ptrace.h>

int show_unhandled_signals = 1;

static int __kprobes spurious_fault(unsigned long write, unsigned long address)
{
	pgd_t *pgd;
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	if (!(address & __UA_LIMIT))
		return 0;

	pgd = pgd_offset_k(address);
	if (!pgd_present(pgdp_get(pgd)))
		return 0;

	p4d = p4d_offset(pgd, address);
	if (!p4d_present(p4dp_get(p4d)))
		return 0;

	pud = pud_offset(p4d, address);
	if (!pud_present(pudp_get(pud)))
		return 0;

	pmd = pmd_offset(pud, address);
	if (!pmd_present(pmdp_get(pmd)))
		return 0;

	if (pmd_leaf(*pmd)) {
		return write ? pmd_write(pmdp_get(pmd)) : 1;
	} else {
		pte = pte_offset_kernel(pmd, address);
		if (!pte_present(ptep_get(pte)))
			return 0;

		return write ? pte_write(ptep_get(pte)) : 1;
	}
}

static void __kprobes no_context(struct pt_regs *regs,
			unsigned long write, unsigned long address)
{
	const int field = sizeof(unsigned long) * 2;

	if (spurious_fault(write, address))
		return;

	/* Are we prepared to handle this kernel fault?	 */
	if (fixup_exception(regs))
		return;

	if (kfence_handle_page_fault(address, write, regs))
		return;

	/*
	 * Oops. The kernel tried to access some bad page. We'll have to
	 * terminate things with extreme prejudice.
	 */
	bust_spinlocks(1);

	pr_alert("CPU %d Unable to handle kernel paging request at "
	       "virtual address %0*lx, era == %0*lx, ra == %0*lx\n",
	       raw_smp_processor_id(), field, address, field, regs->csr_era,
	       field,  regs->regs[1]);
	die("Oops", regs);
}

static void __kprobes do_out_of_memory(struct pt_regs *regs,
			unsigned long write, unsigned long address)
{
	/*
	 * We ran out of memory, call the OOM killer, and return the userspace
	 * (which will retry the fault, or kill us if we got oom-killed).
	 */
	if (!user_mode(regs)) {
		no_context(regs, write, address);
		return;
	}
	pagefault_out_of_memory();
}

static void __kprobes do_sigbus(struct pt_regs *regs,
		unsigned long write, unsigned long address, int si_code)
{
	/* Kernel mode? Handle exceptions or die */
	if (!user_mode(regs)) {
		no_context(regs, write, address);
		return;
	}

	/*
	 * Send a sigbus, regardless of whether we were in kernel
	 * or user mode.
	 */
	current->thread.csr_badvaddr = address;
	current->thread.trap_nr = read_csr_excode();
	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
}

static void __kprobes do_sigsegv(struct pt_regs *regs,
		unsigned long write, unsigned long address, int si_code)
{
	const int field = sizeof(unsigned long) * 2;
	static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);

	/* Kernel mode? Handle exceptions or die */
	if (!user_mode(regs)) {
		no_context(regs, write, address);
		return;
	}

	/* User mode accesses just cause a SIGSEGV */
	current->thread.csr_badvaddr = address;
	if (!write)
		current->thread.error_code = 1;
	else
		current->thread.error_code = 2;
	current->thread.trap_nr = read_csr_excode();

	if (show_unhandled_signals &&
	    unhandled_signal(current, SIGSEGV) && __ratelimit(&ratelimit_state)) {
		pr_info("do_page_fault(): sending SIGSEGV to %s for invalid %s %0*lx\n",
			current->comm,
			write ? "write access to" : "read access from",
			field, address);
		pr_info("era = %0*lx in", field,
			(unsigned long) regs->csr_era);
		print_vma_addr(KERN_CONT " ", regs->csr_era);
		pr_cont("\n");
		pr_info("ra  = %0*lx in", field,
			(unsigned long) regs->regs[1]);
		print_vma_addr(KERN_CONT " ", regs->regs[1]);
		pr_cont("\n");
	}
	force_sig_fault(SIGSEGV, si_code, (void __user *)address);
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
static void __kprobes __do_page_fault(struct pt_regs *regs,
			unsigned long write, unsigned long address)
{
	int si_code = SEGV_MAPERR;
	unsigned int flags = FAULT_FLAG_DEFAULT;
	struct task_struct *tsk = current;
	struct mm_struct *mm = tsk->mm;
	struct vm_area_struct *vma = NULL;
	vm_fault_t fault;

	if (kprobe_page_fault(regs, current->thread.trap_nr))
		return;

	/*
	 * We fault-in kernel-space virtual memory on-demand. The
	 * 'reference' page table is init_mm.pgd.
	 *
	 * NOTE! We MUST NOT take any locks for this case. We may
	 * be in an interrupt or a critical region, and should
	 * only copy the information from the master page table,
	 * nothing more.
	 */
	if (address & __UA_LIMIT) {
		if (!user_mode(regs))
			no_context(regs, write, address);
		else
			do_sigsegv(regs, write, address, si_code);
		return;
	}

	/*
	 * If we're in an interrupt or have no user
	 * context, we must not take the fault..
	 */
	if (faulthandler_disabled() || !mm) {
		do_sigsegv(regs, write, address, si_code);
		return;
	}

	if (user_mode(regs))
		flags |= FAULT_FLAG_USER;

	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
retry:
	vma = lock_mm_and_find_vma(mm, address, regs);
	if (unlikely(!vma))
		goto bad_area_nosemaphore;
	goto good_area;

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
	mmap_read_unlock(mm);
bad_area_nosemaphore:
	do_sigsegv(regs, write, address, si_code);
	return;

/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
	si_code = SEGV_ACCERR;

	if (write) {
		flags |= FAULT_FLAG_WRITE;
		if (!(vma->vm_flags & VM_WRITE))
			goto bad_area;
	} else {
		if (!(vma->vm_flags & VM_EXEC) && address == exception_era(regs))
			goto bad_area;
		if (!(vma->vm_flags & (VM_READ | VM_WRITE)) && address != exception_era(regs))
			goto bad_area;
	}

	/*
	 * 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)) {
		if (!user_mode(regs))
			no_context(regs, write, address);
		return;
	}

	/* The fault is fully completed (including releasing mmap lock) */
	if (fault & VM_FAULT_COMPLETED)
		return;

	if (unlikely(fault & VM_FAULT_RETRY)) {
		flags |= FAULT_FLAG_TRIED;

		/*
		 * No need to mmap_read_unlock(mm) as we would
		 * have already released it in __lock_page_or_retry
		 * in mm/filemap.c.
		 */
		goto retry;
	}
	if (unlikely(fault & VM_FAULT_ERROR)) {
		mmap_read_unlock(mm);
		if (fault & VM_FAULT_OOM) {
			do_out_of_memory(regs, write, address);
			return;
		} else if (fault & VM_FAULT_SIGSEGV) {
			do_sigsegv(regs, write, address, si_code);
			return;
		} else if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
			do_sigbus(regs, write, address, si_code);
			return;
		}
		BUG();
	}

	mmap_read_unlock(mm);
}

asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
			unsigned long write, unsigned long address)
{
	irqentry_state_t state = irqentry_enter(regs);

	/* Enable interrupt if enabled in parent context */
	if (likely(regs->csr_prmd & CSR_PRMD_PIE))
		local_irq_enable();

	__do_page_fault(regs, write, address);

	local_irq_disable();

	irqentry_exit(regs, state);
}