[PATCH v2 0/2] KASAN support for RISC-V

[Nick Hu]

KASAN is an important runtime memory debugging feature in linux kernel
which can detect use-after-free and out-of- bounds problems.

Changes in v2:
- Remove the porting of memmove and exclude the check instead.
- Fix some code noted by Christoph Hellwig

Nick Hu (2):
kasan: Archs don't check memmove if not support it.
riscv: Add KASAN support

arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/kasan.h | 27 ++++++++
arch/riscv/include/asm/pgtable-64.h | 5 ++
arch/riscv/include/asm/string.h | 9 +++
arch/riscv/kernel/head.S | 3 +
arch/riscv/kernel/riscv_ksyms.c | 2 +
arch/riscv/kernel/setup.c | 5 ++
arch/riscv/kernel/vmlinux.lds.S | 1 +
arch/riscv/lib/memcpy.S | 5 +-
arch/riscv/lib/memset.S | 5 +-
arch/riscv/mm/Makefile | 6 ++
arch/riscv/mm/kasan_init.c | 104 ++++++++++++++++++++++++++++
mm/kasan/common.c | 2 +
13 files changed, 171 insertions(+), 4 deletions(-)
create mode 100644 arch/riscv/include/asm/kasan.h
create mode 100644 arch/riscv/mm/kasan_init.c

--
2.17.0

[Nick Hu]

This patch ports the feature Kernel Address SANitizer (KASAN).

Note: The start address of shadow memory is at the beginning of kernel
space, which is 2^64 - (2^39 / 2) in SV39. The size of the kernel space is
2^38 bytes so the size of shadow memory should be 2^38 / 8. Thus, the
shadow memory would not overlap with the fixmap area.

There are currently two limitations in this port,

1. RV64 only: KASAN need large address space for extra shadow memory
region.

2. KASAN can't debug the modules since the modules are allocated in VMALLOC
area. We mapped the shadow memory, which corresponding to VMALLOC area, to
the kasan_early_shadow_page because we don't have enough physical space for
all the shadow memory corresponding to VMALLOC area.

Signed-off-by: Nick Hu <nic...@andestech.com>
---

arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/kasan.h | 27 ++++++++
arch/riscv/include/asm/pgtable-64.h | 5 ++
arch/riscv/include/asm/string.h | 9 +++
arch/riscv/kernel/head.S | 3 +
arch/riscv/kernel/riscv_ksyms.c | 2 +
arch/riscv/kernel/setup.c | 5 ++
arch/riscv/kernel/vmlinux.lds.S | 1 +
arch/riscv/lib/memcpy.S | 5 +-
arch/riscv/lib/memset.S | 5 +-
arch/riscv/mm/Makefile | 6 ++
arch/riscv/mm/kasan_init.c | 104 ++++++++++++++++++++++++++++

12 files changed, 169 insertions(+), 4 deletions(-)

create mode 100644 arch/riscv/include/asm/kasan.h
create mode 100644 arch/riscv/mm/kasan_init.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 8eebbc8860bb..ca2fc8ba8550 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -61,6 +61,7 @@ config RISCV
select SPARSEMEM_STATIC if 32BIT
select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
select HAVE_ARCH_MMAP_RND_BITS
+ select HAVE_ARCH_KASAN if MMU && 64BIT

config ARCH_MMAP_RND_BITS_MIN
default 18 if 64BIT
diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
new file mode 100644
index 000000000000..eb9b1a2f641c
--- /dev/null
+++ b/arch/riscv/include/asm/kasan.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2019 Andes Technology Corporation */
+
+#ifndef __ASM_KASAN_H
+#define __ASM_KASAN_H
+
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_KASAN
+
+#include <asm/pgtable.h>
+
+#define KASAN_SHADOW_SCALE_SHIFT 3
+
+#define KASAN_SHADOW_SIZE (UL(1) << (38 - KASAN_SHADOW_SCALE_SHIFT))
+#define KASAN_SHADOW_START 0xffffffc000000000 // 2^64 - 2^38
+#define KASAN_SHADOW_END (KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
+
+#define KASAN_SHADOW_OFFSET (KASAN_SHADOW_END - (1ULL << \
+ (64 - KASAN_SHADOW_SCALE_SHIFT)))
+
+void kasan_init(void);
+asmlinkage void kasan_early_init(void);
+
+#endif
+#endif
+#endif /* __ASM_KASAN_H */
diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
index 7df8daa66cc8..777a1dddb3df 100644
--- a/arch/riscv/include/asm/pgtable-64.h
+++ b/arch/riscv/include/asm/pgtable-64.h
@@ -59,6 +59,11 @@ static inline unsigned long pud_page_vaddr(pud_t pud)
return (unsigned long)pfn_to_virt(pud_val(pud) >> _PAGE_PFN_SHIFT);
}

+static inline struct page *pud_page(pud_t pud)
+{
+ return pfn_to_page(pud_val(pud) >> _PAGE_PFN_SHIFT);
+}
+
#define pmd_index(addr) (((addr) >> PMD_SHIFT) & (PTRS_PER_PMD - 1))

static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 1b5d44585962..a4451f768826 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -11,8 +11,17 @@

#define __HAVE_ARCH_MEMSET
extern asmlinkage void *memset(void *, int, size_t);
+extern asmlinkage void *__memset(void *, int, size_t);

#define __HAVE_ARCH_MEMCPY
extern asmlinkage void *memcpy(void *, const void *, size_t);
+extern asmlinkage void *__memcpy(void *, const void *, size_t);

+// For those files which don't want to check by kasan.
+#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
+
+#define memcpy(dst, src, len) __memcpy(dst, src, len)
+#define memset(s, c, n) __memset(s, c, n)
+
+#endif
#endif /* _ASM_RISCV_STRING_H */
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 72f89b7590dd..95eca23cd811 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -102,6 +102,9 @@ clear_bss_done:
sw zero, TASK_TI_CPU(tp)
la sp, init_thread_union + THREAD_SIZE

+#ifdef CONFIG_KASAN
+ call kasan_early_init
+#endif
/* Start the kernel */
call parse_dtb
tail start_kernel
diff --git a/arch/riscv/kernel/riscv_ksyms.c b/arch/riscv/kernel/riscv_ksyms.c
index 4800cf703186..376bba7f65ce 100644
--- a/arch/riscv/kernel/riscv_ksyms.c
+++ b/arch/riscv/kernel/riscv_ksyms.c
@@ -14,3 +14,5 @@ EXPORT_SYMBOL(__asm_copy_to_user);
EXPORT_SYMBOL(__asm_copy_from_user);
EXPORT_SYMBOL(memset);
EXPORT_SYMBOL(memcpy);
+EXPORT_SYMBOL(__memset);
+EXPORT_SYMBOL(__memcpy);
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index a990a6cb184f..41f7eae9bc4d 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -23,6 +23,7 @@
#include <asm/smp.h>
#include <asm/tlbflush.h>
#include <asm/thread_info.h>
+#include <asm/kasan.h>

#ifdef CONFIG_DUMMY_CONSOLE
struct screen_info screen_info = {
@@ -70,6 +71,10 @@ void __init setup_arch(char **cmdline_p)
swiotlb_init(1);
#endif

+#ifdef CONFIG_KASAN
+ kasan_init();
+#endif
+
#ifdef CONFIG_SMP
setup_smp();
#endif
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 23cd1a9e52a1..97009803ba9f 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -46,6 +46,7 @@ SECTIONS
KPROBES_TEXT
ENTRY_TEXT
IRQENTRY_TEXT
+ SOFTIRQENTRY_TEXT
*(.fixup)
_etext = .;
}
diff --git a/arch/riscv/lib/memcpy.S b/arch/riscv/lib/memcpy.S
index b4c477846e91..51ab716253fa 100644
--- a/arch/riscv/lib/memcpy.S
+++ b/arch/riscv/lib/memcpy.S
@@ -7,7 +7,8 @@
#include <asm/asm.h>

/* void *memcpy(void *, const void *, size_t) */
-ENTRY(memcpy)
+ENTRY(__memcpy)
+WEAK(memcpy)
move t6, a0 /* Preserve return value */

/* Defer to byte-oriented copy for small sizes */
@@ -104,4 +105,4 @@ ENTRY(memcpy)
bltu a1, a3, 5b
6:
ret
-END(memcpy)
+END(__memcpy)
diff --git a/arch/riscv/lib/memset.S b/arch/riscv/lib/memset.S
index 5a7386b47175..34c5360c6705 100644
--- a/arch/riscv/lib/memset.S
+++ b/arch/riscv/lib/memset.S
@@ -8,7 +8,8 @@
#include <asm/asm.h>

/* void *memset(void *, int, size_t) */
-ENTRY(memset)
+ENTRY(__memset)
+WEAK(memset)
move t0, a0 /* Preserve return value */

/* Defer to byte-oriented fill for small sizes */
@@ -109,4 +110,4 @@ ENTRY(memset)
bltu t0, a3, 5b
6:
ret
-END(memset)
+END(__memset)
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 9d9a17335686..b8a8ca71f86e 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -17,3 +17,9 @@ ifeq ($(CONFIG_MMU),y)
obj-$(CONFIG_SMP) += tlbflush.o
endif
obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
+obj-$(CONFIG_KASAN) += kasan_init.o
+
+ifdef CONFIG_KASAN
+KASAN_SANITIZE_kasan_init.o := n
+KASAN_SANITIZE_init.o := n
+endif
diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
new file mode 100644
index 000000000000..c3152768cdbe
--- /dev/null
+++ b/arch/riscv/mm/kasan_init.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2019 Andes Technology Corporation
+
+#include <linux/pfn.h>
+#include <linux/init_task.h>
+#include <linux/kasan.h>
+#include <linux/kernel.h>
+#include <linux/memblock.h>
+#include <asm/tlbflush.h>
+#include <asm/pgtable.h>
+#include <asm/fixmap.h>
+
+extern pgd_t early_pg_dir[PTRS_PER_PGD];
+asmlinkage void __init kasan_early_init(void)
+{
+ uintptr_t i;
+ pgd_t *pgd = early_pg_dir + pgd_index(KASAN_SHADOW_START);
+
+ for (i = 0; i < PTRS_PER_PTE; ++i)
+ set_pte(kasan_early_shadow_pte + i,
+ mk_pte(virt_to_page(kasan_early_shadow_page),
+ PAGE_KERNEL));
+
+ for (i = 0; i < PTRS_PER_PMD; ++i)
+ set_pmd(kasan_early_shadow_pmd + i,
+ pfn_pmd(PFN_DOWN(__pa((uintptr_t)kasan_early_shadow_pte)),
+ __pgprot(_PAGE_TABLE)));
+
+ for (i = KASAN_SHADOW_START; i < KASAN_SHADOW_END;
+ i += PGDIR_SIZE, ++pgd)
+ set_pgd(pgd,
+ pfn_pgd(PFN_DOWN(__pa(((uintptr_t)kasan_early_shadow_pmd))),
+ __pgprot(_PAGE_TABLE)));
+
+ // init for swapper_pg_dir
+ pgd = pgd_offset_k(KASAN_SHADOW_START);
+
+ for (i = KASAN_SHADOW_START; i < KASAN_SHADOW_END;
+ i += PGDIR_SIZE, ++pgd)
+ set_pgd(pgd,
+ pfn_pgd(PFN_DOWN(__pa(((uintptr_t)kasan_early_shadow_pmd))),
+ __pgprot(_PAGE_TABLE)));
+
+ flush_tlb_all();
+}
+
+static void __init populate(void *start, void *end)
+{
+ unsigned long i;
+ unsigned long vaddr = (unsigned long)start & PAGE_MASK;
+ unsigned long vend = PAGE_ALIGN((unsigned long)end);
+ unsigned long n_pages = (vend - vaddr) / PAGE_SIZE;
+ unsigned long n_pmds =
+ (n_pages % PTRS_PER_PTE) ? n_pages / PTRS_PER_PTE + 1 :
+ n_pages / PTRS_PER_PTE;
+ pgd_t *pgd = pgd_offset_k(vaddr);
+ pmd_t *pmd = memblock_alloc(n_pmds * sizeof(pmd_t), PAGE_SIZE);
+ pte_t *pte = memblock_alloc(n_pages * sizeof(pte_t), PAGE_SIZE);
+
+ for (i = 0; i < n_pages; i++) {
+ phys_addr_t phys = memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
+
+ set_pte(pte + i, pfn_pte(PHYS_PFN(phys), PAGE_KERNEL));
+ }
+
+ for (i = 0; i < n_pages; ++pmd, i += PTRS_PER_PTE)
+ set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa((uintptr_t)(pte + i))),
+ __pgprot(_PAGE_TABLE)));
+
+ for (i = vaddr; i < vend; i += PGDIR_SIZE, ++pgd)
+ set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa(((uintptr_t)pmd))),
+ __pgprot(_PAGE_TABLE)));
+
+ flush_tlb_all();
+ memset(start, 0, end - start);
+}
+
+void __init kasan_init(void)
+{
+ struct memblock_region *reg;
+ unsigned long i;
+
+ kasan_populate_early_shadow((void *)KASAN_SHADOW_START,
+ (void *)kasan_mem_to_shadow((void *)VMALLOC_END));
+
+ for_each_memblock(memory, reg) {
+ void *start = (void *)__va(reg->base);
+ void *end = (void *)__va(reg->base + reg->size);
+
+ if (start >= end)
+ break;
+
+ populate(kasan_mem_to_shadow(start),
+ kasan_mem_to_shadow(end));
+ };
+
+ for (i = 0; i < PTRS_PER_PTE; i++)
+ set_pte(&kasan_early_shadow_pte[i],
+ mk_pte(virt_to_page(kasan_early_shadow_page),
+ __pgprot(_PAGE_PRESENT | _PAGE_READ | _PAGE_ACCESSED)));
+
+ memset(kasan_early_shadow_page, 0, PAGE_SIZE);
+ init_task.kasan_depth = 0;
+}
--
2.17.0

[Andrey Konovalov]

On Wed, Oct 2, 2019 at 8:16 AM Nick Hu <nic...@andestech.com> wrote:
>
> This patch ports the feature Kernel Address SANitizer (KASAN).

Hi Nick,

Please also update KASAN documentation to mention that riscv is supported.

Thanks!

> --
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[Nick Hu]

KASAN is an important runtime memory debugging feature in linux kernel

which can detect use-after-free and out-of-bounds problems.

Changes in v2:
- Remove the porting of memmove and exclude the check instead.
- Fix some code noted by Christoph Hellwig

Changes in v3:
- Update the KASAN documentation to mention that riscv is supported.

Nick Hu (3):

kasan: Archs don't check memmove if not support it.
riscv: Add KASAN support

kasan: Add riscv to KASAN documentation.

Documentation/dev-tools/kasan.rst | 4 +-

arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/kasan.h | 27 ++++++++
arch/riscv/include/asm/pgtable-64.h | 5 ++
arch/riscv/include/asm/string.h | 9 +++
arch/riscv/kernel/head.S | 3 +
arch/riscv/kernel/riscv_ksyms.c | 2 +
arch/riscv/kernel/setup.c | 5 ++
arch/riscv/kernel/vmlinux.lds.S | 1 +
arch/riscv/lib/memcpy.S | 5 +-
arch/riscv/lib/memset.S | 5 +-
arch/riscv/mm/Makefile | 6 ++
arch/riscv/mm/kasan_init.c | 104 ++++++++++++++++++++++++++++

mm/kasan/common.c | 2 +
14 files changed, 173 insertions(+), 6 deletions(-)

create mode 100644 arch/riscv/include/asm/kasan.h
create mode 100644 arch/riscv/mm/kasan_init.c

--
2.17.0

[Nick Hu]

Skip the memmove checking for those archs who don't support it.

Signed-off-by: Nick Hu <nic...@andestech.com>
---

mm/kasan/common.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6814d6d6a023..897f9520bab3 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -107,6 +107,7 @@ void *memset(void *addr, int c, size_t len)
return __memset(addr, c, len);
}

+#ifdef __HAVE_ARCH_MEMMOVE
#undef memmove
void *memmove(void *dest, const void *src, size_t len)
{
@@ -115,6 +116,7 @@ void *memmove(void *dest, const void *src, size_t len)

return __memmove(dest, src, len);
}
+#endif

#undef memcpy
void *memcpy(void *dest, const void *src, size_t len)
--
2.17.0

[Nick Hu]

This patch ports the feature Kernel Address SANitizer (KASAN).

Note: The start address of shadow memory is at the beginning of kernel
space, which is 2^64 - (2^39 / 2) in SV39. The size of the kernel space is
2^38 bytes so the size of shadow memory should be 2^38 / 8. Thus, the
shadow memory would not overlap with the fixmap area.

There are currently two limitations in this port,

1. RV64 only: KASAN need large address space for extra shadow memory
region.

2. KASAN can't debug the modules since the modules are allocated in VMALLOC
area. We mapped the shadow memory, which corresponding to VMALLOC area, to
the kasan_early_shadow_page because we don't have enough physical space for
all the shadow memory corresponding to VMALLOC area.

Signed-off-by: Nick Hu <nic...@andestech.com>
---

arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/kasan.h | 27 ++++++++
arch/riscv/include/asm/pgtable-64.h | 5 ++
arch/riscv/include/asm/string.h | 9 +++
arch/riscv/kernel/head.S | 3 +
arch/riscv/kernel/riscv_ksyms.c | 2 +
arch/riscv/kernel/setup.c | 5 ++
arch/riscv/kernel/vmlinux.lds.S | 1 +
arch/riscv/lib/memcpy.S | 5 +-
arch/riscv/lib/memset.S | 5 +-
arch/riscv/mm/Makefile | 6 ++
arch/riscv/mm/kasan_init.c | 104 ++++++++++++++++++++++++++++

12 files changed, 169 insertions(+), 4 deletions(-)

create mode 100644 arch/riscv/include/asm/kasan.h
create mode 100644 arch/riscv/mm/kasan_init.c

[Nick Hu]

Add riscv to the KASAN documentation to mention that riscv
is supporting generic kasan now.

Signed-off-by: Nick Hu <nic...@andestech.com>
---

Documentation/dev-tools/kasan.rst | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index b72d07d70239..34fbb7212cbc 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -21,8 +21,8 @@ global variables yet.

Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later.

-Currently generic KASAN is supported for the x86_64, arm64, xtensa and s390
-architectures, and tag-based KASAN is supported only for arm64.
+Currently generic KASAN is supported for the x86_64, arm64, xtensa, s390 and
+riscv architectures, and tag-based KASAN is supported only for arm64.

Usage
-----
--
2.17.0

[Palmer Dabbelt]

I think this is backwards: we shouldn't be defining an arch-specific memmove
symbol when KASAN is enabled. If we do it this way then we're defeating the
memmove checks, which doesn't seem like the right way to go.

[Andrey Ryabinin]

On 10/8/19 9:11 AM, Nick Hu wrote:
> Skip the memmove checking for those archs who don't support it.

The patch is fine but the changelog sounds misleading. We don't skip memmove checking.
If arch don't have memmove than the C implementation from lib/string.c used.
It's instrumented by compiler so it's checked and we simply don't need that KASAN's memmove with
manual checks.

[Paul Walmsley]

On Thu, 17 Oct 2019, Andrey Ryabinin wrote:

> On 10/8/19 9:11 AM, Nick Hu wrote:
> > Skip the memmove checking for those archs who don't support it.
>
> The patch is fine but the changelog sounds misleading. We don't skip memmove checking.
> If arch don't have memmove than the C implementation from lib/string.c used.
> It's instrumented by compiler so it's checked and we simply don't need that KASAN's memmove with
> manual checks.

Thanks Andrey. Nick, could you please update the patch description?

- Paul

[Greentime Hu]

Nick Hu <nic...@andestech.com> 於 2019年10月8日 週二 下午2:17寫道：

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> + __pgprot(_PAGE_TABLE)));
> +

Hi Nick,

I verify this patch in Qemu and Unleashed board.
I found it works well if DRAM size is less than 4GB.
It will get an access fault if the DRAM size is larger than 4GB.

I spend some time to debug this case and I found it hang in the
following memset().
It is because the mapping is not created correctly. I check the page
table creating logic again and I found it always sets the last pmd
here.

[Nick Hu]

Thanks! I would update the description in v4 patch.

Nick

[Nick Hu]

Hi Greentime,

Thanks! I would fix it in v4 patch.

Nick.