LoongArch: Add KFENCE (Kernel Electric-Fence) support

The LoongArch architecture is quite different from other architectures.
When the allocating of KFENCE itself is done, it is mapped to the direct
mapping configuration window [1] by default on LoongArch.  It means that
it is not possible to use the page table mapped mode which required by
the KFENCE system and therefore it should be remapped to the appropriate
region.

This patch adds architecture specific implementation details for KFENCE.
In particular, this implements the required interface in <asm/kfence.h>.

Tested this patch by running the testcases and all passed.

[1] https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#virtual-address-space-and-address-translation-mode

Signed-off-by: Enze Li <lienze@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

2 files changed, 71 insertions, 1 deletions

diff --git a/arch/loongarch/include/asm/kfence.h b/arch/loongarch/include/asm/kfence.h
new file mode 100644
index 000000000000..6c82aea1c993
--- /dev/null
+++ b/arch/loongarch/include/asm/kfence.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KFENCE support for LoongArch.
+ *
+ * Author: Enze Li <lienze@kylinos.cn>
+ * Copyright (C) 2022-2023 KylinSoft Corporation.
+ */
+
+#ifndef _ASM_LOONGARCH_KFENCE_H
+#define _ASM_LOONGARCH_KFENCE_H
+
+#include <linux/kfence.h>
+#include <asm/pgtable.h>
+#include <asm/tlb.h>
+
+static inline bool arch_kfence_init_pool(void)
+{
+	int err;
+	char *kfence_pool = __kfence_pool;
+	struct vm_struct *area;
+
+	area = __get_vm_area_caller(KFENCE_POOL_SIZE, VM_IOREMAP,
+				    KFENCE_AREA_START, KFENCE_AREA_END,
+				    __builtin_return_address(0));
+	if (!area)
+		return false;
+
+	__kfence_pool = (char *)area->addr;
+	err = ioremap_page_range((unsigned long)__kfence_pool,
+				 (unsigned long)__kfence_pool + KFENCE_POOL_SIZE,
+				 virt_to_phys((void *)kfence_pool), PAGE_KERNEL);
+	if (err) {
+		free_vm_area(area);
+		__kfence_pool = kfence_pool;
+		return false;
+	}
+
+	return true;
+}
+
+/* Protect the given page and flush TLB. */
+static inline bool kfence_protect_page(unsigned long addr, bool protect)
+{
+	pte_t *pte = virt_to_kpte(addr);
+
+	if (WARN_ON(!pte) || pte_none(*pte))
+		return false;
+
+	if (protect)
+		set_pte(pte, __pte(pte_val(*pte) & ~(_PAGE_VALID | _PAGE_PRESENT)));
+	else
+		set_pte(pte, __pte(pte_val(*pte) | (_PAGE_VALID | _PAGE_PRESENT)));
+
+	preempt_disable();
+	local_flush_tlb_one(addr);
+	preempt_enable();
+
+	return true;
+}
+
+#endif /* _ASM_LOONGARCH_KFENCE_H */
diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index 338d1b147464..7e3708883994 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -82,14 +82,23 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define MODULES_VADDR	(vm_map_base + PCI_IOSIZE + (2 * PAGE_SIZE))
 #define MODULES_END	(MODULES_VADDR + SZ_256M)
 
+#ifdef CONFIG_KFENCE
+#define KFENCE_AREA_SIZE	(((CONFIG_KFENCE_NUM_OBJECTS + 1) * 2 + 2) * PAGE_SIZE)
+#else
+#define KFENCE_AREA_SIZE	0
+#endif
+
 #define VMALLOC_START	MODULES_END
 #define VMALLOC_END	\
 	(vm_map_base +	\
-	 min(PTRS_PER_PGD * PTRS_PER_PUD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE, (1UL << cpu_vabits)) - PMD_SIZE - VMEMMAP_SIZE)
+	 min(PTRS_PER_PGD * PTRS_PER_PUD * PTRS_PER_PMD * PTRS_PER_PTE * PAGE_SIZE, (1UL << cpu_vabits)) - PMD_SIZE - VMEMMAP_SIZE - KFENCE_AREA_SIZE)
 
 #define vmemmap		((struct page *)((VMALLOC_END + PMD_SIZE) & PMD_MASK))
 #define VMEMMAP_END	((unsigned long)vmemmap + VMEMMAP_SIZE - 1)
 
+#define KFENCE_AREA_START	(VMEMMAP_END + 1)
+#define KFENCE_AREA_END		(KFENCE_AREA_START + KFENCE_AREA_SIZE - 1)
+
 #define pte_ERROR(e) \
 	pr_err("%s:%d: bad pte %016lx.\n", __FILE__, __LINE__, pte_val(e))
 #ifndef __PAGETABLE_PMD_FOLDED