[RFC PATCH v1] powerpc: Enable KFENCE for PPC32

Christophe Leroy
2021-03-02T09:21:37Z

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