[RFC PATCH v1] powerpc: Enable KFENCE for PPC32

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Add architecture specific implementation details for KFENCE and enable
KFENCE for the ppc32 architecture. In particular, this implements the
required interface in <asm/kfence.h>.

KFENCE requires that attributes for pages from its memory pool can
individually be set. Therefore, force the Read/Write linear map to be
mapped at page granularity.

Unit tests succeed on all tests but one:

	[   15.053324]     # test_invalid_access: EXPECTATION FAILED at mm/kfence/kfence_test.c:636
	[   15.053324]     Expected report_matches(&expect) to be true, but is false
	[   15.068359]     not ok 21 - test_invalid_access

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/Kconfig              | 13 +++++++------
 arch/powerpc/include/asm/kfence.h | 32 +++++++++++++++++++++++++++++++
 arch/powerpc/mm/book3s32/mmu.c    |  2 +-
 arch/powerpc/mm/fault.c           |  7 ++++++-
 arch/powerpc/mm/init_32.c         |  3 +++
 arch/powerpc/mm/nohash/8xx.c      |  5 +++--
 6 files changed, 52 insertions(+), 10 deletions(-)
 create mode 100644 arch/powerpc/include/asm/kfence.h

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 386ae12d8523..d46db0bfb998 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -185,6 +185,7 @@ config PPC
 	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
 	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
 	select HAVE_ARCH_KGDB
+	select HAVE_ARCH_KFENCE			if PPC32
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
 	select HAVE_ARCH_NVRAM_OPS
@@ -786,7 +787,7 @@ config THREAD_SHIFT
 config DATA_SHIFT_BOOL
 	bool "Set custom data alignment"
 	depends on ADVANCED_OPTIONS
-	depends on STRICT_KERNEL_RWX || DEBUG_PAGEALLOC
+	depends on STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE
 	depends on PPC_BOOK3S_32 || (PPC_8xx && !PIN_TLB_DATA && !STRICT_KERNEL_RWX)
 	help
 	  This option allows you to set the kernel data alignment. When
@@ -798,13 +799,13 @@ config DATA_SHIFT_BOOL
 config DATA_SHIFT
 	int "Data shift" if DATA_SHIFT_BOOL
 	default 24 if STRICT_KERNEL_RWX && PPC64
-	range 17 28 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC) && PPC_BOOK3S_32
-	range 19 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC) && PPC_8xx
+	range 17 28 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) && PPC_BOOK3S_32
+	range 19 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC || KFENCE) && PPC_8xx
 	default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
-	default 18 if DEBUG_PAGEALLOC && PPC_BOOK3S_32
+	default 18 if (DEBUG_PAGEALLOC || KFENCE) && PPC_BOOK3S_32
 	default 23 if STRICT_KERNEL_RWX && PPC_8xx
-	default 23 if DEBUG_PAGEALLOC && PPC_8xx && PIN_TLB_DATA
-	default 19 if DEBUG_PAGEALLOC && PPC_8xx
+	default 23 if (DEBUG_PAGEALLOC || KFENCE) && PPC_8xx && PIN_TLB_DATA
+	default 19 if (DEBUG_PAGEALLOC || KFENCE) && PPC_8xx
 	default PPC_PAGE_SHIFT
 	help
 	  On Book3S 32 (603+), DBATs are used to map kernel text and rodata RO.
diff --git a/arch/powerpc/include/asm/kfence.h b/arch/powerpc/include/asm/kfence.h
new file mode 100644
index 000000000000..c229ee6a48f0
--- /dev/null
+++ b/arch/powerpc/include/asm/kfence.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * powerpc KFENCE support.
+ *
+ * Copyright (C) 2020 CS GROUP France
+ */
+
+#ifndef __ASM_POWERPC_KFENCE_H
+#define __ASM_POWERPC_KFENCE_H
+
+#include <asm/pgtable.h>
+
+static inline bool arch_kfence_init_pool(void)
+{
+	return true;
+}
+
+static inline bool kfence_protect_page(unsigned long addr, bool protect)
+{
+	pte_t *kpte = virt_to_kpte(addr);
+
+	if (protect) {
+		pte_update(&init_mm, addr, kpte, _PAGE_PRESENT, 0, 0);
+		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+	} else {
+		pte_update(&init_mm, addr, kpte, 0, _PAGE_PRESENT, 0);
+	}
+
+	return true;
+}
+
+#endif /* __ASM_POWERPC_KFENCE_H */
diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
index d7eb266a3f7a..4548aec95561 100644
--- a/arch/powerpc/mm/book3s32/mmu.c
+++ b/arch/powerpc/mm/book3s32/mmu.c
@@ -162,7 +162,7 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 	unsigned long border = (unsigned long)__init_begin - PAGE_OFFSET;
 
 
-	if (debug_pagealloc_enabled() || __map_without_bats) {
+	if (debug_pagealloc_enabled() || __map_without_bats || IS_ENABLED(CONFIG_KFENCE)) {
 		pr_debug_once("Read-Write memory mapped without BATs\n");
 		if (base >= border)
 			return base;
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index bb368257b55c..bea13682c909 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -32,6 +32,7 @@
 #include <linux/context_tracking.h>
 #include <linux/hugetlb.h>
 #include <linux/uaccess.h>
+#include <linux/kfence.h>
 
 #include <asm/firmware.h>
 #include <asm/interrupt.h>
@@ -418,8 +419,12 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 	 * 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)))
+	if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) {
+		if (kfence_handle_page_fault(address, is_write, regs))
+			return 0;
+
 		return SIGSEGV;
+	}
 
 	/*
 	 * If we're in an interrupt, have no user context or are running
diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
index 02c7db4087cb..3d690be48e84 100644
--- a/arch/powerpc/mm/init_32.c
+++ b/arch/powerpc/mm/init_32.c
@@ -97,6 +97,9 @@ static void __init MMU_setup(void)
 	if (IS_ENABLED(CONFIG_PPC_8xx))
 		return;
 
+	if (IS_ENABLED(CONFIG_KFENCE))
+		__map_without_ltlbs = 1;
+
 	if (debug_pagealloc_enabled())
 		__map_without_ltlbs = 1;
 
diff --git a/arch/powerpc/mm/nohash/8xx.c b/arch/powerpc/mm/nohash/8xx.c
index 19a3eec1d8c5..17051377aed7 100644
--- a/arch/powerpc/mm/nohash/8xx.c
+++ b/arch/powerpc/mm/nohash/8xx.c
@@ -149,7 +149,8 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 {
 	unsigned long etext8 = ALIGN(__pa(_etext), SZ_8M);
 	unsigned long sinittext = __pa(_sinittext);
-	bool strict_boundary = strict_kernel_rwx_enabled() || debug_pagealloc_enabled();
+	bool strict_boundary = strict_kernel_rwx_enabled() || debug_pagealloc_enabled() ||
+			       IS_ENABLED(CONFIG_KFENCE);
 	unsigned long boundary = strict_boundary ? sinittext : etext8;
 	unsigned long einittext8 = ALIGN(__pa(_einittext), SZ_8M);
 
@@ -161,7 +162,7 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 		return 0;
 
 	mmu_mapin_ram_chunk(0, boundary, PAGE_KERNEL_TEXT, true);
-	if (debug_pagealloc_enabled()) {
+	if (debug_pagealloc_enabled() || IS_ENABLED(CONFIG_KFENCE)) {
 		top = boundary;
 	} else {
 		mmu_mapin_ram_chunk(boundary, einittext8, PAGE_KERNEL_TEXT, true);
-- 
2.25.0