arch/powerpc/mm/fault.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  PowerPC version
  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  *
  *  Derived from "arch/i386/mm/fault.c"
  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *
  *  Modified by Cort Dougan and Paul Mackerras.
  *
  *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
  */

 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/pagemap.h>
 #include <linux/ptrace.h>
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/interrupt.h>
 #include <linux/highmem.h>
 #include <linux/extable.h>
 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
 #include <linux/perf_event.h>
 #include <linux/ratelimit.h>
 #include <linux/context_tracking.h>
 #include <linux/hugetlb.h>
 #include <linux/uaccess.h>

 #include <asm/firmware.h>
 #include <asm/page.h>
 #include <asm/mmu.h>
 #include <asm/mmu_context.h>
 #include <asm/siginfo.h>
 #include <asm/debug.h>
 #include <asm/kup.h>
 #include <asm/inst.h>


 /*
  * do_page_fault error handling helpers
  */

 static int
 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
 {
 	/*
 	 * If we are in kernel mode, bail out with a SEGV, this will
 	 * be caught by the assembly which will restore the non-volatile
 	 * registers before calling bad_page_fault()
 	 */
 	if (!user_mode(regs))
 		return SIGSEGV;

 	_exception(SIGSEGV, regs, si_code, address);

 	return 0;
 }

 static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
 {
 	return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
 }

 static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
 {
 	struct mm_struct *mm = current->mm;

 	/*
 	 * Something tried to access memory that isn't in our memory map..
 	 * Fix it, but check if it's kernel or user first..
 	 */
 	mmap_read_unlock(mm);

 	return __bad_area_nosemaphore(regs, address, si_code);
 }

 static noinline int bad_area(struct pt_regs *regs, unsigned long address)
 {
 	return __bad_area(regs, address, SEGV_MAPERR);
 }

 #ifdef CONFIG_PPC_MEM_KEYS
 static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
 				    struct vm_area_struct *vma)
 {
 	struct mm_struct *mm = current->mm;
 	int pkey;

 	/*
 	 * We don't try to fetch the pkey from page table because reading
 	 * page table without locking doesn't guarantee stable pte value.
 	 * Hence the pkey value that we return to userspace can be different
 	 * from the pkey that actually caused access error.
 	 *
 	 * It does *not* guarantee that the VMA we find here
 	 * was the one that we faulted on.
 	 *
 	 * 1. T1   : mprotect_key(foo, PAGE_SIZE, pkey=4);
 	 * 2. T1   : set AMR to deny access to pkey=4, touches, page
 	 * 3. T1   : faults...
 	 * 4.    T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
 	 * 5. T1   : enters fault handler, takes mmap_lock, etc...
 	 * 6. T1   : reaches here, sees vma_pkey(vma)=5, when we really
 	 *	     faulted on a pte with its pkey=4.
 	 */
 	pkey = vma_pkey(vma);

 	mmap_read_unlock(mm);

 	/*
 	 * If we are in kernel mode, bail out with a SEGV, this will
 	 * be caught by the assembly which will restore the non-volatile
 	 * registers before calling bad_page_fault()
 	 */
 	if (!user_mode(regs))
 		return SIGSEGV;

 	_exception_pkey(regs, address, pkey);

 	return 0;
 }
 #endif

 static noinline int bad_access(struct pt_regs *regs, unsigned long address)
 {
 	return __bad_area(regs, address, SEGV_ACCERR);
 }

 static int do_sigbus(struct pt_regs *regs, unsigned long address,
 		     vm_fault_t fault)
 {
 	if (!user_mode(regs))
 		return SIGBUS;

 	current->thread.trap_nr = BUS_ADRERR;
 #ifdef CONFIG_MEMORY_FAILURE
 	if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
 		unsigned int lsb = 0; /* shutup gcc */

 		pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
 			current->comm, current->pid, address);

 		if (fault & VM_FAULT_HWPOISON_LARGE)
 			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
 		if (fault & VM_FAULT_HWPOISON)
 			lsb = PAGE_SHIFT;

 		force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
 		return 0;
 	}

 #endif
 	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
 	return 0;
 }

 static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
 				vm_fault_t fault)
 {
 	/*
 	 * Kernel page fault interrupted by SIGKILL. We have no reason to
 	 * continue processing.
 	 */
 	if (fatal_signal_pending(current) && !user_mode(regs))
 		return SIGKILL;

 	/* Out of memory */
 	if (fault & VM_FAULT_OOM) {
 		/*
 		 * We ran out of memory, or some other thing happened to us that
 		 * made us unable to handle the page fault gracefully.
 		 */
 		if (!user_mode(regs))
 			return SIGSEGV;
 		pagefault_out_of_memory();
 	} else {
 		if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
 			     VM_FAULT_HWPOISON_LARGE))
 			return do_sigbus(regs, addr, fault);
 		else if (fault & VM_FAULT_SIGSEGV)
 			return bad_area_nosemaphore(regs, addr);
 		else
 			BUG();
 	}
 	return 0;
 }

 /* Is this a bad kernel fault ? */
 static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
 			     unsigned long address, bool is_write)
 {
 	int is_exec = TRAP(regs) == 0x400;

 	if (is_exec) {
 		pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
 				    address >= TASK_SIZE ? "exec-protected" : "user",
 				    address,
 				    from_kuid(&init_user_ns, current_uid()));

 		// Kernel exec fault is always bad
 		return true;
 	}

 	if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
 	    !search_exception_tables(regs->nip)) {
 		pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
 				    address,
 				    from_kuid(&init_user_ns, current_uid()));
 	}

 	// Kernel fault on kernel address is bad
 	if (address >= TASK_SIZE)
 		return true;

 	// Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
 	if (!search_exception_tables(regs->nip))
 		return true;

 	// Read/write fault in a valid region (the exception table search passed
 	// above), but blocked by KUAP is bad, it can never succeed.
 	if (bad_kuap_fault(regs, address, is_write))
 		return true;

 	// What's left? Kernel fault on user in well defined regions (extable
 	// matched), and allowed by KUAP in the faulting context.
 	return false;
 }

 #ifdef CONFIG_PPC_MEM_KEYS
 static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey,
 			      struct vm_area_struct *vma)
 {
 	/*
 	 * Make sure to check the VMA so that we do not perform
 	 * faults just to hit a pkey fault as soon as we fill in a
 	 * page. Only called for current mm, hence foreign == 0
 	 */
 	if (!arch_vma_access_permitted(vma, is_write, is_exec, 0))
 		return true;

 	return false;
 }
 #endif

 static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma)
 {
 	/*
 	 * Allow execution from readable areas if the MMU does not
 	 * provide separate controls over reading and executing.
 	 *
 	 * Note: That code used to not be enabled for 4xx/BookE.
 	 * It is now as I/D cache coherency for these is done at
 	 * set_pte_at() time and I see no reason why the test
 	 * below wouldn't be valid on those processors. This -may-
 	 * break programs compiled with a really old ABI though.
 	 */
 	if (is_exec) {
 		return !(vma->vm_flags & VM_EXEC) &&
 			(cpu_has_feature(CPU_FTR_NOEXECUTE) ||
 			 !(vma->vm_flags & (VM_READ | VM_WRITE)));
 	}

 	if (is_write) {
 		if (unlikely(!(vma->vm_flags & VM_WRITE)))
 			return true;
 		return false;
 	}

 	if (unlikely(!vma_is_accessible(vma)))
 		return true;
 	/*
 	 * We should ideally do the vma pkey access check here. But in the
 	 * fault path, handle_mm_fault() also does the same check. To avoid
 	 * these multiple checks, we skip it here and handle access error due
 	 * to pkeys later.
 	 */
 	return false;
 }

 #ifdef CONFIG_PPC_SMLPAR
 static inline void cmo_account_page_fault(void)
 {
 	if (firmware_has_feature(FW_FEATURE_CMO)) {
 		u32 page_ins;

 		preempt_disable();
 		page_ins = be32_to_cpu(get_lppaca()->page_ins);
 		page_ins += 1 << PAGE_FACTOR;
 		get_lppaca()->page_ins = cpu_to_be32(page_ins);
 		preempt_enable();
 	}
 }
 #else
 static inline void cmo_account_page_fault(void) { }
 #endif /* CONFIG_PPC_SMLPAR */

 static void sanity_check_fault(bool is_write, bool is_user,
 			       unsigned long error_code, unsigned long address)
 {
 	/*
 	 * Userspace trying to access kernel address, we get PROTFAULT for that.
 	 */
 	if (is_user && address >= TASK_SIZE) {
 		if ((long)address == -1)
 			return;

 		pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
 				   current->comm, current->pid, address,
 				   from_kuid(&init_user_ns, current_uid()));
 		return;
 	}

 	if (!IS_ENABLED(CONFIG_PPC_BOOK3S))
 		return;

 	/*
 	 * For hash translation mode, we should never get a
 	 * PROTFAULT. Any update to pte to reduce access will result in us
 	 * removing the hash page table entry, thus resulting in a DSISR_NOHPTE
 	 * fault instead of DSISR_PROTFAULT.
 	 *
 	 * A pte update to relax the access will not result in a hash page table
 	 * entry invalidate and hence can result in DSISR_PROTFAULT.
 	 * ptep_set_access_flags() doesn't do a hpte flush. This is why we have
 	 * the special !is_write in the below conditional.
 	 *
 	 * For platforms that doesn't supports coherent icache and do support
 	 * per page noexec bit, we do setup things such that we do the
 	 * sync between D/I cache via fault. But that is handled via low level
 	 * hash fault code (hash_page_do_lazy_icache()) and we should not reach
 	 * here in such case.
 	 *
 	 * For wrong access that can result in PROTFAULT, the above vma->vm_flags
 	 * check should handle those and hence we should fall to the bad_area
 	 * handling correctly.
 	 *
 	 * For embedded with per page exec support that doesn't support coherent
 	 * icache we do get PROTFAULT and we handle that D/I cache sync in
 	 * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
 	 * is conditional for server MMU.
 	 *
 	 * For radix, we can get prot fault for autonuma case, because radix
 	 * page table will have them marked noaccess for user.
 	 */
 	if (radix_enabled() || is_write)
 		return;

 	WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
 }

 /*
  * Define the correct "is_write" bit in error_code based
  * on the processor family
  */
 #if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 #define page_fault_is_write(__err)	((__err) & ESR_DST)
 #define page_fault_is_bad(__err)	(0)
 #else
 #define page_fault_is_write(__err)	((__err) & DSISR_ISSTORE)
 #if defined(CONFIG_PPC_8xx)
 #define page_fault_is_bad(__err)	((__err) & DSISR_NOEXEC_OR_G)
 #elif defined(CONFIG_PPC64)
 #define page_fault_is_bad(__err)	((__err) & DSISR_BAD_FAULT_64S)
 #else
 #define page_fault_is_bad(__err)	((__err) & DSISR_BAD_FAULT_32S)
 #endif
 #endif

 /*
  * For 600- and 800-family processors, the error_code parameter is DSISR
  * for a data fault, SRR1 for an instruction fault. For 400-family processors
  * the error_code parameter is ESR for a data fault, 0 for an instruction
  * fault.
  * For 64-bit processors, the error_code parameter is
  *  - DSISR for a non-SLB data access fault,
  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
  *  - 0 any SLB fault.
  *
  * The return value is 0 if the fault was handled, or the signal
  * number if this is a kernel fault that can't be handled here.
  */
 static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 			   unsigned long error_code)
 {
 	struct vm_area_struct * vma;
 	struct mm_struct *mm = current->mm;
 	unsigned int flags = FAULT_FLAG_DEFAULT;
  	int is_exec = TRAP(regs) == 0x400;
 	int is_user = user_mode(regs);
 	int is_write = page_fault_is_write(error_code);
 	vm_fault_t fault, major = 0;
 	bool kprobe_fault = kprobe_page_fault(regs, 11);

 	if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
 		return 0;

 	if (unlikely(page_fault_is_bad(error_code))) {
 		if (is_user) {
 			_exception(SIGBUS, regs, BUS_OBJERR, address);
 			return 0;
 		}
 		return SIGBUS;
 	}

 	/* Additional sanity check(s) */
 	sanity_check_fault(is_write, is_user, error_code, address);

 	/*
 	 * The kernel should never take an execute fault nor should it
 	 * take a page fault to a kernel address or a page fault to a user
 	 * address outside of dedicated places
 	 */
 	if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write)))
 		return SIGSEGV;

 	/*
 	 * If we're in an interrupt, have no user context or are running
 	 * in a region with pagefaults disabled then we must not take the fault
 	 */
 	if (unlikely(faulthandler_disabled() || !mm)) {
 		if (is_user)
 			printk_ratelimited(KERN_ERR "Page fault in user mode"
 					   " with faulthandler_disabled()=%d"
 					   " mm=%p\n",
 					   faulthandler_disabled(), mm);
 		return bad_area_nosemaphore(regs, address);
 	}

 	/* We restore the interrupt state now */
 	if (!arch_irq_disabled_regs(regs))
 		local_irq_enable();

 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

 	/*
 	 * We want to do this outside mmap_lock, because reading code around nip
 	 * can result in fault, which will cause a deadlock when called with
 	 * mmap_lock held
 	 */
 	if (is_user)
 		flags |= FAULT_FLAG_USER;
 	if (is_write)
 		flags |= FAULT_FLAG_WRITE;
 	if (is_exec)
 		flags |= FAULT_FLAG_INSTRUCTION;

 	/* When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in the
 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
 	 * erroneous fault occurring in a code path which already holds mmap_lock
 	 * we will deadlock attempting to validate the fault against the
 	 * address space.  Luckily the kernel only validly references user
 	 * space from well defined areas of code, which are listed in the
 	 * exceptions table.
 	 *
 	 * As the vast majority of faults will be valid we will only perform
 	 * the source reference check when there is a possibility of a deadlock.
 	 * Attempt to lock the address space, if we cannot we then validate the
 	 * source.  If this is invalid we can skip the address space check,
 	 * thus avoiding the deadlock.
 	 */
 	if (unlikely(!mmap_read_trylock(mm))) {
 		if (!is_user && !search_exception_tables(regs->nip))
 			return bad_area_nosemaphore(regs, address);

 retry:
 		mmap_read_lock(mm);
 	} else {
 		/*
 		 * The above down_read_trylock() might have succeeded in
 		 * which case we'll have missed the might_sleep() from
 		 * down_read():
 		 */
 		might_sleep();
 	}

 	vma = find_vma(mm, address);
 	if (unlikely(!vma))
 		return bad_area(regs, address);

 	if (unlikely(vma->vm_start > address)) {
 		if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
 			return bad_area(regs, address);

 		if (unlikely(expand_stack(vma, address)))
 			return bad_area(regs, address);
 	}

 #ifdef CONFIG_PPC_MEM_KEYS
 	if (unlikely(access_pkey_error(is_write, is_exec,
 				       (error_code & DSISR_KEYFAULT), vma)))
 		return bad_access_pkey(regs, address, vma);
 #endif /* CONFIG_PPC_MEM_KEYS */

 	if (unlikely(access_error(is_write, is_exec, vma)))
 		return bad_access(regs, address);

 	/*
 	 * 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);

 	major |= fault & VM_FAULT_MAJOR;

 	if (fault_signal_pending(fault, regs))
 		return user_mode(regs) ? 0 : SIGBUS;

 	/*
 	 * Handle the retry right now, the mmap_lock has been released in that
 	 * case.
 	 */
 	if (unlikely(fault & VM_FAULT_RETRY)) {
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
 			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}

 	mmap_read_unlock(current->mm);

 	if (unlikely(fault & VM_FAULT_ERROR))
 		return mm_fault_error(regs, address, fault);

 	/*
 	 * Major/minor page fault accounting.
 	 */
 	if (major)
 		cmo_account_page_fault();

 	return 0;
 }
 NOKPROBE_SYMBOL(__do_page_fault);

 int do_page_fault(struct pt_regs *regs, unsigned long address,
 		  unsigned long error_code)
 {
 	enum ctx_state prev_state = exception_enter();
 	int rc = __do_page_fault(regs, address, error_code);
 	exception_exit(prev_state);
 	return rc;
 }
 NOKPROBE_SYMBOL(do_page_fault);

 /*
  * bad_page_fault is called when we have a bad access from the kernel.
  * It is called from the DSI and ISI handlers in head.S and from some
  * of the procedures in traps.c.
  */
 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 {
 	const struct exception_table_entry *entry;
 	int is_write = page_fault_is_write(regs->dsisr);

 	/* Are we prepared to handle this fault?  */
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
 		regs->nip = extable_fixup(entry);
 		return;
 	}

 	/* kernel has accessed a bad area */

 	switch (TRAP(regs)) {
 	case 0x300:
 	case 0x380:
 	case 0xe00:
 		pr_alert("BUG: %s on %s at 0x%08lx\n",
 			 regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
 			 "Unable to handle kernel data access",
 			 is_write ? "write" : "read", regs->dar);
 		break;
 	case 0x400:
 	case 0x480:
 		pr_alert("BUG: Unable to handle kernel instruction fetch%s",
 			 regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
 		break;
 	case 0x600:
 		pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
 			 regs->dar);
 		break;
 	default:
 		pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
 			 regs->dar);
 		break;
 	}
 	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 		regs->nip);

 	if (task_stack_end_corrupted(current))
 		printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");

 	die("Kernel access of bad area", regs, sig);
 }
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* PowerPC version
	* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
	*
	* Derived from "arch/i386/mm/fault.c"
	* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
	*
	* Modified by Cort Dougan and Paul Mackerras.
	*
	* Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
	*/

	#include <linux/signal.h>
	#include <linux/sched.h>
	#include <linux/sched/task_stack.h>
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/pagemap.h>
	#include <linux/ptrace.h>
	#include <linux/mman.h>
	#include <linux/mm.h>
	#include <linux/interrupt.h>
	#include <linux/highmem.h>
	#include <linux/extable.h>
	#include <linux/kprobes.h>
	#include <linux/kdebug.h>
	#include <linux/perf_event.h>
	#include <linux/ratelimit.h>
	#include <linux/context_tracking.h>
	#include <linux/hugetlb.h>
	#include <linux/uaccess.h>

	#include <asm/firmware.h>
	#include <asm/page.h>
	#include <asm/mmu.h>
	#include <asm/mmu_context.h>
	#include <asm/siginfo.h>
	#include <asm/debug.h>
	#include <asm/kup.h>
	#include <asm/inst.h>


	/*
	* do_page_fault error handling helpers
	*/

	static int
	__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
	{
	/*
	* If we are in kernel mode, bail out with a SEGV, this will
	* be caught by the assembly which will restore the non-volatile
	* registers before calling bad_page_fault()
	*/
	if (!user_mode(regs))
	return SIGSEGV;

	_exception(SIGSEGV, regs, si_code, address);

	return 0;
	}

	static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
	{
	return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
	}

	static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
	{
	struct mm_struct *mm = current->mm;

	/*
	* Something tried to access memory that isn't in our memory map..
	* Fix it, but check if it's kernel or user first..
	*/
	mmap_read_unlock(mm);

	return __bad_area_nosemaphore(regs, address, si_code);
	}

	static noinline int bad_area(struct pt_regs *regs, unsigned long address)
	{
	return __bad_area(regs, address, SEGV_MAPERR);
	}

	#ifdef CONFIG_PPC_MEM_KEYS
	static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
	struct vm_area_struct *vma)
	{
	struct mm_struct *mm = current->mm;
	int pkey;

	/*
	* We don't try to fetch the pkey from page table because reading
	* page table without locking doesn't guarantee stable pte value.
	* Hence the pkey value that we return to userspace can be different
	* from the pkey that actually caused access error.
	*
	* It does not guarantee that the VMA we find here
	* was the one that we faulted on.
	*
	* 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
	* 2. T1 : set AMR to deny access to pkey=4, touches, page
	* 3. T1 : faults...
	* 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
	* 5. T1 : enters fault handler, takes mmap_lock, etc...
	* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
	* faulted on a pte with its pkey=4.
	*/
	pkey = vma_pkey(vma);

	mmap_read_unlock(mm);

	/*
	* If we are in kernel mode, bail out with a SEGV, this will
	* be caught by the assembly which will restore the non-volatile
	* registers before calling bad_page_fault()
	*/
	if (!user_mode(regs))
	return SIGSEGV;

	_exception_pkey(regs, address, pkey);

	return 0;
	}
	#endif

	static noinline int bad_access(struct pt_regs *regs, unsigned long address)
	{
	return __bad_area(regs, address, SEGV_ACCERR);
	}

	static int do_sigbus(struct pt_regs *regs, unsigned long address,
	vm_fault_t fault)
	{
	if (!user_mode(regs))
	return SIGBUS;

	current->thread.trap_nr = BUS_ADRERR;
	#ifdef CONFIG_MEMORY_FAILURE
	if (fault & (VM_FAULT_HWPOISON\|VM_FAULT_HWPOISON_LARGE)) {
	unsigned int lsb = 0; /* shutup gcc */

	pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
	current->comm, current->pid, address);

	if (fault & VM_FAULT_HWPOISON_LARGE)
	lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
	if (fault & VM_FAULT_HWPOISON)
	lsb = PAGE_SHIFT;

	force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
	return 0;
	}

	#endif
	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
	return 0;
	}

	static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
	vm_fault_t fault)
	{
	/*
	* Kernel page fault interrupted by SIGKILL. We have no reason to
	* continue processing.
	*/
	if (fatal_signal_pending(current) && !user_mode(regs))
	return SIGKILL;

	/* Out of memory */
	if (fault & VM_FAULT_OOM) {
	/*
	* We ran out of memory, or some other thing happened to us that
	* made us unable to handle the page fault gracefully.
	*/
	if (!user_mode(regs))
	return SIGSEGV;
	pagefault_out_of_memory();
	} else {
	if (fault & (VM_FAULT_SIGBUS\|VM_FAULT_HWPOISON\|
	VM_FAULT_HWPOISON_LARGE))
	return do_sigbus(regs, addr, fault);
	else if (fault & VM_FAULT_SIGSEGV)
	return bad_area_nosemaphore(regs, addr);
	else
	BUG();
	}
	return 0;
	}

	/* Is this a bad kernel fault ? */
	static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
	unsigned long address, bool is_write)
	{
	int is_exec = TRAP(regs) == 0x400;

	if (is_exec) {
	pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
	address >= TASK_SIZE ? "exec-protected" : "user",
	address,
	from_kuid(&init_user_ns, current_uid()));

	// Kernel exec fault is always bad
	return true;
	}

	if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
	!search_exception_tables(regs->nip)) {
	pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
	address,
	from_kuid(&init_user_ns, current_uid()));
	}

	// Kernel fault on kernel address is bad
	if (address >= TASK_SIZE)
	return true;

	// Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
	if (!search_exception_tables(regs->nip))
	return true;

	// Read/write fault in a valid region (the exception table search passed
	// above), but blocked by KUAP is bad, it can never succeed.
	if (bad_kuap_fault(regs, address, is_write))
	return true;

	// What's left? Kernel fault on user in well defined regions (extable
	// matched), and allowed by KUAP in the faulting context.
	return false;
	}

	#ifdef CONFIG_PPC_MEM_KEYS
	static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey,
	struct vm_area_struct *vma)
	{
	/*
	* Make sure to check the VMA so that we do not perform
	* faults just to hit a pkey fault as soon as we fill in a
	* page. Only called for current mm, hence foreign == 0
	*/
	if (!arch_vma_access_permitted(vma, is_write, is_exec, 0))
	return true;

	return false;
	}
	#endif

	static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma)
	{
	/*
	* Allow execution from readable areas if the MMU does not
	* provide separate controls over reading and executing.
	*
	* Note: That code used to not be enabled for 4xx/BookE.
	* It is now as I/D cache coherency for these is done at
	* set_pte_at() time and I see no reason why the test
	* below wouldn't be valid on those processors. This -may-
	* break programs compiled with a really old ABI though.
	*/
	if (is_exec) {
	return !(vma->vm_flags & VM_EXEC) &&
	(cpu_has_feature(CPU_FTR_NOEXECUTE) \|\|
	!(vma->vm_flags & (VM_READ \| VM_WRITE)));
	}

	if (is_write) {
	if (unlikely(!(vma->vm_flags & VM_WRITE)))
	return true;
	return false;
	}

	if (unlikely(!vma_is_accessible(vma)))
	return true;
	/*
	* We should ideally do the vma pkey access check here. But in the
	* fault path, handle_mm_fault() also does the same check. To avoid
	* these multiple checks, we skip it here and handle access error due
	* to pkeys later.
	*/
	return false;
	}

	#ifdef CONFIG_PPC_SMLPAR
	static inline void cmo_account_page_fault(void)
	{
	if (firmware_has_feature(FW_FEATURE_CMO)) {
	u32 page_ins;

	preempt_disable();
	page_ins = be32_to_cpu(get_lppaca()->page_ins);
	page_ins += 1 << PAGE_FACTOR;
	get_lppaca()->page_ins = cpu_to_be32(page_ins);
	preempt_enable();
	}
	}
	#else
	static inline void cmo_account_page_fault(void) { }
	#endif /* CONFIG_PPC_SMLPAR */

	static void sanity_check_fault(bool is_write, bool is_user,
	unsigned long error_code, unsigned long address)
	{
	/*
	* Userspace trying to access kernel address, we get PROTFAULT for that.
	*/
	if (is_user && address >= TASK_SIZE) {
	if ((long)address == -1)
	return;

	pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
	current->comm, current->pid, address,
	from_kuid(&init_user_ns, current_uid()));
	return;
	}

	if (!IS_ENABLED(CONFIG_PPC_BOOK3S))
	return;

	/*
	* For hash translation mode, we should never get a
	* PROTFAULT. Any update to pte to reduce access will result in us
	* removing the hash page table entry, thus resulting in a DSISR_NOHPTE
	* fault instead of DSISR_PROTFAULT.
	*
	* A pte update to relax the access will not result in a hash page table
	* entry invalidate and hence can result in DSISR_PROTFAULT.
	* ptep_set_access_flags() doesn't do a hpte flush. This is why we have
	* the special !is_write in the below conditional.
	*
	* For platforms that doesn't supports coherent icache and do support
	* per page noexec bit, we do setup things such that we do the
	* sync between D/I cache via fault. But that is handled via low level
	* hash fault code (hash_page_do_lazy_icache()) and we should not reach
	* here in such case.
	*
	* For wrong access that can result in PROTFAULT, the above vma->vm_flags
	* check should handle those and hence we should fall to the bad_area
	* handling correctly.
	*
	* For embedded with per page exec support that doesn't support coherent
	* icache we do get PROTFAULT and we handle that D/I cache sync in
	* set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
	* is conditional for server MMU.
	*
	* For radix, we can get prot fault for autonuma case, because radix
	* page table will have them marked noaccess for user.
	*/
	if (radix_enabled() \|\| is_write)
	return;

	WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
	}

	/*
	* Define the correct "is_write" bit in error_code based
	* on the processor family
	*/
	#if (defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE))
	#define page_fault_is_write(__err) ((__err) & ESR_DST)
	#define page_fault_is_bad(__err) (0)
	#else
	#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE)
	#if defined(CONFIG_PPC_8xx)
	#define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G)
	#elif defined(CONFIG_PPC64)
	#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_64S)
	#else
	#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S)
	#endif
	#endif

	/*
	* For 600- and 800-family processors, the error_code parameter is DSISR
	* for a data fault, SRR1 for an instruction fault. For 400-family processors
	* the error_code parameter is ESR for a data fault, 0 for an instruction
	* fault.
	* For 64-bit processors, the error_code parameter is
	* - DSISR for a non-SLB data access fault,
	* - SRR1 & 0x08000000 for a non-SLB instruction access fault
	* - 0 any SLB fault.
	*
	* The return value is 0 if the fault was handled, or the signal
	* number if this is a kernel fault that can't be handled here.
	*/
	static int __do_page_fault(struct pt_regs *regs, unsigned long address,
	unsigned long error_code)
	{
	struct vm_area_struct * vma;
	struct mm_struct *mm = current->mm;
	unsigned int flags = FAULT_FLAG_DEFAULT;
	int is_exec = TRAP(regs) == 0x400;
	int is_user = user_mode(regs);
	int is_write = page_fault_is_write(error_code);
	vm_fault_t fault, major = 0;
	bool kprobe_fault = kprobe_page_fault(regs, 11);

	if (unlikely(debugger_fault_handler(regs) \|\| kprobe_fault))
	return 0;

	if (unlikely(page_fault_is_bad(error_code))) {
	if (is_user) {
	_exception(SIGBUS, regs, BUS_OBJERR, address);
	return 0;
	}
	return SIGBUS;
	}

	/* Additional sanity check(s) */
	sanity_check_fault(is_write, is_user, error_code, address);

	/*
	* The kernel should never take an execute fault nor should it
	* take a page fault to a kernel address or a page fault to a user
	* address outside of dedicated places
	*/
	if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write)))
	return SIGSEGV;

	/*
	* If we're in an interrupt, have no user context or are running
	* in a region with pagefaults disabled then we must not take the fault
	*/
	if (unlikely(faulthandler_disabled() \|\| !mm)) {
	if (is_user)
	printk_ratelimited(KERN_ERR "Page fault in user mode"
	" with faulthandler_disabled()=%d"
	" mm=%p\n",
	faulthandler_disabled(), mm);
	return bad_area_nosemaphore(regs, address);
	}

	/* We restore the interrupt state now */
	if (!arch_irq_disabled_regs(regs))
	local_irq_enable();

	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

	/*
	* We want to do this outside mmap_lock, because reading code around nip
	* can result in fault, which will cause a deadlock when called with
	* mmap_lock held
	*/
	if (is_user)
	flags \|= FAULT_FLAG_USER;
	if (is_write)
	flags \|= FAULT_FLAG_WRITE;
	if (is_exec)
	flags \|= FAULT_FLAG_INSTRUCTION;

	/* When running in the kernel we expect faults to occur only to
	* addresses in user space. All other faults represent errors in the
	* kernel and should generate an OOPS. Unfortunately, in the case of an
	* erroneous fault occurring in a code path which already holds mmap_lock
	* we will deadlock attempting to validate the fault against the
	* address space. Luckily the kernel only validly references user
	* space from well defined areas of code, which are listed in the
	* exceptions table.
	*
	* As the vast majority of faults will be valid we will only perform
	* the source reference check when there is a possibility of a deadlock.
	* Attempt to lock the address space, if we cannot we then validate the
	* source. If this is invalid we can skip the address space check,
	* thus avoiding the deadlock.
	*/
	if (unlikely(!mmap_read_trylock(mm))) {
	if (!is_user && !search_exception_tables(regs->nip))
	return bad_area_nosemaphore(regs, address);

	retry:
	mmap_read_lock(mm);
	} else {
	/*
	* The above down_read_trylock() might have succeeded in
	* which case we'll have missed the might_sleep() from
	* down_read():
	*/
	might_sleep();
	}

	vma = find_vma(mm, address);
	if (unlikely(!vma))
	return bad_area(regs, address);

	if (unlikely(vma->vm_start > address)) {
	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
	return bad_area(regs, address);

	if (unlikely(expand_stack(vma, address)))
	return bad_area(regs, address);
	}

	#ifdef CONFIG_PPC_MEM_KEYS
	if (unlikely(access_pkey_error(is_write, is_exec,
	(error_code & DSISR_KEYFAULT), vma)))
	return bad_access_pkey(regs, address, vma);
	#endif /* CONFIG_PPC_MEM_KEYS */

	if (unlikely(access_error(is_write, is_exec, vma)))
	return bad_access(regs, address);

	/*
	* 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);

	major \|= fault & VM_FAULT_MAJOR;

	if (fault_signal_pending(fault, regs))
	return user_mode(regs) ? 0 : SIGBUS;

	/*
	* Handle the retry right now, the mmap_lock has been released in that
	* case.
	*/
	if (unlikely(fault & VM_FAULT_RETRY)) {
	if (flags & FAULT_FLAG_ALLOW_RETRY) {
	flags \|= FAULT_FLAG_TRIED;
	goto retry;
	}
	}

	mmap_read_unlock(current->mm);

	if (unlikely(fault & VM_FAULT_ERROR))
	return mm_fault_error(regs, address, fault);

	/*
	* Major/minor page fault accounting.
	*/
	if (major)
	cmo_account_page_fault();

	return 0;
	}
	NOKPROBE_SYMBOL(__do_page_fault);

	int do_page_fault(struct pt_regs *regs, unsigned long address,
	unsigned long error_code)
	{
	enum ctx_state prev_state = exception_enter();
	int rc = __do_page_fault(regs, address, error_code);
	exception_exit(prev_state);
	return rc;
	}
	NOKPROBE_SYMBOL(do_page_fault);

	/*
	* bad_page_fault is called when we have a bad access from the kernel.
	* It is called from the DSI and ISI handlers in head.S and from some
	* of the procedures in traps.c.
	*/
	void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
	{
	const struct exception_table_entry *entry;
	int is_write = page_fault_is_write(regs->dsisr);

	/* Are we prepared to handle this fault? */
	if ((entry = search_exception_tables(regs->nip)) != NULL) {
	regs->nip = extable_fixup(entry);
	return;
	}

	/* kernel has accessed a bad area */

	switch (TRAP(regs)) {
	case 0x300:
	case 0x380:
	case 0xe00:
	pr_alert("BUG: %s on %s at 0x%08lx\n",
	regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
	"Unable to handle kernel data access",
	is_write ? "write" : "read", regs->dar);
	break;
	case 0x400:
	case 0x480:
	pr_alert("BUG: Unable to handle kernel instruction fetch%s",
	regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
	break;
	case 0x600:
	pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
	regs->dar);
	break;
	default:
	pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
	regs->dar);
	break;
	}
	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
	regs->nip);

	if (task_stack_end_corrupted(current))
	printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");

	die("Kernel access of bad area", regs, sig);
	}