1 files changed, 162 insertions, 88 deletions

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index efa402025031..2bc828a1940c 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -17,6 +17,7 @@
 #include <linux/sched/debug.h>
 #include <linux/highmem.h>
 #include <linux/perf_event.h>
+#include <linux/kfence.h>
 
 #include <asm/system_misc.h>
 #include <asm/system_info.h>
@@ -26,6 +27,13 @@
 
 #ifdef CONFIG_MMU
 
+bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
+{
+	unsigned long addr = (unsigned long)unsafe_src;
+
+	return addr >= TASK_SIZE && ULONG_MAX - addr >= size;
+}
+
 /*
  * This is useful to dump out the page tables associated with
  * 'addr' in mm 'mm'.
@@ -37,7 +45,6 @@ void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
 	if (!mm)
 		mm = &init_mm;
 
-	printk("%spgd = %p\n", lvl, mm->pgd);
 	pgd = pgd_offset(mm, addr);
 	printk("%s[%08lx] *pgd=%08llx", lvl, addr, (long long)pgd_val(*pgd));
 
@@ -85,6 +92,9 @@ void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
 			break;
 
 		pte = pte_offset_map(pmd, addr);
+		if (!pte)
+			break;
+
 		pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
 #ifndef CONFIG_ARM_LPAE
 		pr_cont(", *ppte=%08llx",
@@ -100,6 +110,39 @@ void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
 { }
 #endif					/* CONFIG_MMU */
 
+static inline bool is_write_fault(unsigned int fsr)
+{
+	return (fsr & FSR_WRITE) && !(fsr & FSR_CM);
+}
+
+static inline bool is_translation_fault(unsigned int fsr)
+{
+	int fs = fsr_fs(fsr);
+#ifdef CONFIG_ARM_LPAE
+	if ((fs & FS_MMU_NOLL_MASK) == FS_TRANS_NOLL)
+		return true;
+#else
+	if (fs == FS_L1_TRANS || fs == FS_L2_TRANS)
+		return true;
+#endif
+	return false;
+}
+
+static void die_kernel_fault(const char *msg, struct mm_struct *mm,
+			     unsigned long addr, unsigned int fsr,
+			     struct pt_regs *regs)
+{
+	bust_spinlocks(1);
+	pr_alert("8<--- cut here ---\n");
+	pr_alert("Unable to handle kernel %s at virtual address %08lx when %s\n",
+		 msg, addr, fsr & FSR_LNX_PF ? "execute" : str_write_read(fsr & FSR_WRITE));
+
+	show_pte(KERN_ALERT, mm, addr);
+	die("Oops", regs, fsr);
+	bust_spinlocks(0);
+	make_task_dead(SIGKILL);
+}
+
 /*
  * Oops.  The kernel tried to access some page that wasn't present.
  */
@@ -107,6 +150,7 @@ static void
 __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
 		  struct pt_regs *regs)
 {
+	const char *msg;
 	/*
 	 * Are we prepared to handle this kernel fault?
 	 */
@@ -116,16 +160,17 @@ __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
 	/*
 	 * No handler, we'll have to terminate things with extreme prejudice.
 	 */
-	bust_spinlocks(1);
-	pr_alert("8<--- cut here ---\n");
-	pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
-		 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
-		 "paging request", addr);
+	if (addr < PAGE_SIZE) {
+		msg = "NULL pointer dereference";
+	} else {
+		if (is_translation_fault(fsr) &&
+		    kfence_handle_page_fault(addr, is_write_fault(fsr), regs))
+			return;
 
-	show_pte(KERN_ALERT, mm, addr);
-	die("Oops", regs, fsr);
-	bust_spinlocks(0);
-	do_exit(SIGKILL);
+		msg = "paging request";
+	}
+
+	die_kernel_fault(msg, mm, addr, fsr, regs);
 }
 
 /*
@@ -180,76 +225,53 @@ void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 }
 
 #ifdef CONFIG_MMU
-#define VM_FAULT_BADMAP		0x010000
-#define VM_FAULT_BADACCESS	0x020000
-
-/*
- * Check that the permissions on the VMA allow for the fault which occurred.
- * If we encountered a write fault, we must have write permission, otherwise
- * we allow any permission.
- */
-static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
+static inline bool is_permission_fault(unsigned int fsr)
 {
-	unsigned int mask = VM_ACCESS_FLAGS;
-
-	if ((fsr & FSR_WRITE) && !(fsr & FSR_CM))
-		mask = VM_WRITE;
-	if (fsr & FSR_LNX_PF)
-		mask = VM_EXEC;
-
-	return vma->vm_flags & mask ? false : true;
+	int fs = fsr_fs(fsr);
+#ifdef CONFIG_ARM_LPAE
+	if ((fs & FS_MMU_NOLL_MASK) == FS_PERM_NOLL)
+		return true;
+#else
+	if (fs == FS_L1_PERM || fs == FS_L2_PERM)
+		return true;
+#endif
+	return false;
 }
 
-static vm_fault_t __kprobes
-__do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
-		unsigned int flags, struct task_struct *tsk,
-		struct pt_regs *regs)
+#ifdef CONFIG_CPU_TTBR0_PAN
+static inline bool ttbr0_usermode_access_allowed(struct pt_regs *regs)
 {
-	struct vm_area_struct *vma;
-	vm_fault_t fault;
+	struct svc_pt_regs *svcregs;
 
-	vma = find_vma(mm, addr);
-	fault = VM_FAULT_BADMAP;
-	if (unlikely(!vma))
-		goto out;
-	if (unlikely(vma->vm_start > addr))
-		goto check_stack;
-
-	/*
-	 * Ok, we have a good vm_area for this
-	 * memory access, so we can handle it.
-	 */
-good_area:
-	if (access_error(fsr, vma)) {
-		fault = VM_FAULT_BADACCESS;
-		goto out;
-	}
+	/* If we are in user mode: permission granted */
+	if (user_mode(regs))
+		return true;
 
-	return handle_mm_fault(vma, addr & PAGE_MASK, flags, regs);
+	/* uaccess state saved above pt_regs on SVC exception entry */
+	svcregs = to_svc_pt_regs(regs);
 
-check_stack:
-	/* Don't allow expansion below FIRST_USER_ADDRESS */
-	if (vma->vm_flags & VM_GROWSDOWN &&
-	    addr >= FIRST_USER_ADDRESS && !expand_stack(vma, addr))
-		goto good_area;
-out:
-	return fault;
+	return !(svcregs->ttbcr & TTBCR_EPD0);
+}
+#else
+static inline bool ttbr0_usermode_access_allowed(struct pt_regs *regs)
+{
+	return true;
 }
+#endif
 
 static int __kprobes
 do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 {
-	struct task_struct *tsk;
-	struct mm_struct *mm;
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
 	int sig, code;
 	vm_fault_t fault;
 	unsigned int flags = FAULT_FLAG_DEFAULT;
+	vm_flags_t vm_flags = VM_ACCESS_FLAGS;
 
 	if (kprobe_page_fault(regs, fsr))
 		return 0;
 
-	tsk = current;
-	mm  = tsk->mm;
 
 	/* Enable interrupts if they were enabled in the parent context. */
 	if (interrupts_enabled(regs))
@@ -264,36 +286,84 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
-	if ((fsr & FSR_WRITE) && !(fsr & FSR_CM))
+
+	if (is_write_fault(fsr)) {
 		flags |= FAULT_FLAG_WRITE;
+		vm_flags = VM_WRITE;
+	}
+
+	if (fsr & FSR_LNX_PF) {
+		vm_flags = VM_EXEC;
+
+		if (is_permission_fault(fsr) && !user_mode(regs))
+			die_kernel_fault("execution of memory",
+					 mm, addr, fsr, regs);
+	}
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 
 	/*
-	 * As per x86, we may deadlock here.  However, since the kernel only
-	 * validly references user space from well defined areas of the code,
-	 * we can bug out early if this is from code which shouldn't.
+	 * Privileged access aborts with CONFIG_CPU_TTBR0_PAN enabled are
+	 * routed via the translation fault mechanism. Check whether uaccess
+	 * is disabled while in kernel mode.
 	 */
-	if (!mmap_read_trylock(mm)) {
-		if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
+	if (!ttbr0_usermode_access_allowed(regs))
+		goto no_context;
+
+	if (!(flags & FAULT_FLAG_USER))
+		goto lock_mmap;
+
+	vma = lock_vma_under_rcu(mm, addr);
+	if (!vma)
+		goto lock_mmap;
+
+	if (!(vma->vm_flags & vm_flags)) {
+		vma_end_read(vma);
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+		fault = 0;
+		code = SEGV_ACCERR;
+		goto bad_area;
+	}
+	fault = handle_mm_fault(vma, addr, 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);
+		goto done;
+	}
+	count_vm_vma_lock_event(VMA_LOCK_RETRY);
+	if (fault & VM_FAULT_MAJOR)
+		flags |= FAULT_FLAG_TRIED;
+
+	/* Quick path to respond to signals */
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
 			goto no_context;
+		return 0;
+	}
+lock_mmap:
+
 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();
-#ifdef CONFIG_DEBUG_VM
-		if (!user_mode(regs) &&
-		    !search_exception_tables(regs->ARM_pc))
-			goto no_context;
-#endif
+	vma = lock_mm_and_find_vma(mm, addr, regs);
+	if (unlikely(!vma)) {
+		fault = 0;
+		code = SEGV_MAPERR;
+		goto bad_area;
 	}
 
-	fault = __do_page_fault(mm, addr, fsr, flags, tsk, regs);
+	/*
+	 * ok, we have a good vm_area for this memory access, check the
+	 * permissions on the VMA allow for the fault which occurred.
+	 */
+	if (!(vma->vm_flags & vm_flags)) {
+		mmap_read_unlock(mm);
+		fault = 0;
+		code = SEGV_ACCERR;
+		goto bad_area;
+	}
+
+	fault = handle_mm_fault(vma, addr & PAGE_MASK, flags, regs);
 
 	/* If we need to retry but a fatal signal is pending, handle the
 	 * signal first. We do not need to release the mmap_lock because
@@ -305,7 +375,11 @@ retry:
 		return 0;
 	}
 
-	if (!(fault & VM_FAULT_ERROR) && flags & FAULT_FLAG_ALLOW_RETRY) {
+	/* The fault is fully completed (including releasing mmap lock) */
+	if (fault & VM_FAULT_COMPLETED)
+		return 0;
+
+	if (!(fault & VM_FAULT_ERROR)) {
 		if (fault & VM_FAULT_RETRY) {
 			flags |= FAULT_FLAG_TRIED;
 			goto retry;
@@ -313,13 +387,14 @@ retry:
 	}
 
 	mmap_read_unlock(mm);
+done:
 
-	/*
-	 * Handle the "normal" case first - VM_FAULT_MAJOR
-	 */
-	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
+	/* Handle the "normal" case first */
+	if (likely(!(fault & VM_FAULT_ERROR)))
 		return 0;
 
+	code = SEGV_MAPERR;
+bad_area:
 	/*
 	 * If we are in kernel mode at this point, we
 	 * have no context to handle this fault with.
@@ -350,8 +425,6 @@ retry:
 		 * isn't in our memory map..
 		 */
 		sig = SIGSEGV;
-		code = fault == VM_FAULT_BADACCESS ?
-			SEGV_ACCERR : SEGV_MAPERR;
 	}
 
 	__do_user_fault(addr, fsr, sig, code, regs);
@@ -552,6 +625,7 @@ do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
 	if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
 		return;
 
+	pr_alert("8<--- cut here ---\n");
 	pr_alert("Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
 		inf->name, ifsr, addr);