[PATCH v2 0/5] kasan: support stack instrumentation for tag-based mode

[PATCH v2 0/5] kasan: support stack instrumentation for tag-based mode

[Andrey Konovalov]

This goes on top of Walter's patch titled "kasan: fix KASAN unit tests
for tag-based KASAN" (already in mm tree).

Bugzilla link: https://bugzilla.kernel.org/show_bug.cgi?id=203497

Thanks to Walter Wu for debugging and testing.

Changes v1 -> v2:
- Add efi patch to undefined reference to `efi_enter_virtual_mode'.
- Reorder attributes for start_kernel().

Andrey Konovalov (5):
  kasan: don't tag stacks allocated with pagealloc
  efi: provide empty efi_enter_virtual_mode implementation
  kasan, arm64: don't instrument functions that enable kasan
  kasan: allow enabling stack tagging for tag-based mode
  kasan: adjust kasan_stack_oob for tag-based mode

 arch/arm64/kernel/setup.c | 2 +-
 include/linux/efi.h       | 4 ++++
 init/main.c               | 2 +-
 kernel/fork.c             | 3 ++-
 lib/test_kasan.c          | 2 +-
 scripts/Makefile.kasan    | 3 ++-
 6 files changed, 11 insertions(+), 5 deletions(-)

-- 
2.28.0.163.g6104cc2f0b6-goog

[PATCH v2 1/5] kasan: don't tag stacks allocated with pagealloc

[Andrey Konovalov]

This patch prepares Software Tag-Based KASAN for stack tagging support.

With Tag-Based KASAN when kernel stacks are allocated via pagealloc
(which happens when CONFIG_VMAP_STACK is not enabled), they get tagged.
KASAN instrumentation doesn't expect the sp register to be tagged, and
this leads to false-positive reports.

Fix by resetting the tag of kernel stack pointers after allocation.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 kernel/fork.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index efc5493203ae..75415f5e647c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -261,7 +261,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 					     THREAD_SIZE_ORDER);
 
 	if (likely(page)) {
-		tsk->stack = page_address(page);
+		tsk->stack = kasan_reset_tag(page_address(page));
 		return tsk->stack;
 	}
 	return NULL;
@@ -307,6 +307,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
 {
 	unsigned long *stack;
 	stack = kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
+	stack = kasan_reset_tag(stack);
 	tsk->stack = stack;
 	return stack;
 }
-- 
2.28.0.163.g6104cc2f0b6-goog

[PATCH v2 2/5] efi: provide empty efi_enter_virtual_mode implementation

[Andrey Konovalov]

When CONFIG_EFI is not enabled, we might get an undefined reference
to efi_enter_virtual_mode() error, if this efi_enabled() call isn't
inlined into start_kernel(). This happens in particular, if start_kernel()
is annodated with __no_sanitize_address.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/efi.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/efi.h b/include/linux/efi.h
index 05c47f857383..73db1ae04cef 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -606,7 +606,11 @@ extern void *efi_get_pal_addr (void);
 extern void efi_map_pal_code (void);
 extern void efi_memmap_walk (efi_freemem_callback_t callback, void *arg);
 extern void efi_gettimeofday (struct timespec64 *ts);
+#ifdef CONFIG_EFI
 extern void efi_enter_virtual_mode (void);	/* switch EFI to virtual mode, if possible */
+#else
+static inline void efi_enter_virtual_mode (void) {}
+#endif
 #ifdef CONFIG_X86
 extern efi_status_t efi_query_variable_store(u32 attributes,
 					     unsigned long size,
-- 
2.28.0.163.g6104cc2f0b6-goog

Re: [PATCH v2 2/5] efi: provide empty efi_enter_virtual_mode implementation

[Ard Biesheuvel]

On Tue, 4 Aug 2020 at 14:41, Andrey Konovalov <andreyknvl@google.com> wrote:
>
> When CONFIG_EFI is not enabled, we might get an undefined reference
> to efi_enter_virtual_mode() error, if this efi_enabled() call isn't
> inlined into start_kernel(). This happens in particular, if start_kernel()
> is annodated with __no_sanitize_address.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  include/linux/efi.h | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 05c47f857383..73db1ae04cef 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -606,7 +606,11 @@ extern void *efi_get_pal_addr (void);
>  extern void efi_map_pal_code (void);
>  extern void efi_memmap_walk (efi_freemem_callback_t callback, void *arg);
>  extern void efi_gettimeofday (struct timespec64 *ts);
> +#ifdef CONFIG_EFI
>  extern void efi_enter_virtual_mode (void);     /* switch EFI to virtual mode, if possible */
> +#else
> +static inline void efi_enter_virtual_mode (void) {}
> +#endif
>  #ifdef CONFIG_X86
>  extern efi_status_t efi_query_variable_store(u32 attributes,
>                                              unsigned long size,
> --
> 2.28.0.163.g6104cc2f0b6-goog
>

[PATCH v2 3/5] kasan, arm64: don't instrument functions that enable kasan

[Andrey Konovalov]

This patch prepares Software Tag-Based KASAN for stack tagging support.

With stack tagging enabled, KASAN tags stack variable in each function
in its prologue. In start_kernel() stack variables get tagged before KASAN
is enabled via setup_arch()->kasan_init(). As the result the tags for
start_kernel()'s stack variables end up in the temporary shadow memory.
Later when KASAN gets enabled, switched to normal shadow, and starts
checking tags, this leads to false-positive reports, as proper tags are
missing in normal shadow.

Disable KASAN instrumentation for start_kernel(). Also disable it for
arm64's setup_arch() as a precaution (it doesn't have any stack variables
right now).

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/kernel/setup.c | 2 +-
 init/main.c               | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 93b3844cf442..575da075a2b9 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -276,7 +276,7 @@ arch_initcall(reserve_memblock_reserved_regions);
 
 u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
 
-void __init setup_arch(char **cmdline_p)
+void __init __no_sanitize_address setup_arch(char **cmdline_p)
 {
 	init_mm.start_code = (unsigned long) _text;
 	init_mm.end_code   = (unsigned long) _etext;
diff --git a/init/main.c b/init/main.c
index 0ead83e86b5a..7e5e25d9fe42 100644
--- a/init/main.c
+++ b/init/main.c
@@ -827,7 +827,7 @@ void __init __weak arch_call_rest_init(void)
 	rest_init();
 }
 
-asmlinkage __visible void __init start_kernel(void)
+asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 {
 	char *command_line;
 	char *after_dashes;
-- 
2.28.0.163.g6104cc2f0b6-goog

Re: [PATCH v2 3/5] kasan, arm64: don't instrument functions that enable kasan

[Catalin Marinas]

On Tue, Aug 04, 2020 at 02:41:26PM +0200, Andrey Konovalov wrote:
> This patch prepares Software Tag-Based KASAN for stack tagging support.
> 
> With stack tagging enabled, KASAN tags stack variable in each function
> in its prologue. In start_kernel() stack variables get tagged before KASAN
> is enabled via setup_arch()->kasan_init(). As the result the tags for
> start_kernel()'s stack variables end up in the temporary shadow memory.
> Later when KASAN gets enabled, switched to normal shadow, and starts
> checking tags, this leads to false-positive reports, as proper tags are
> missing in normal shadow.
> 
> Disable KASAN instrumentation for start_kernel(). Also disable it for
> arm64's setup_arch() as a precaution (it doesn't have any stack variables
> right now).
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

I thought I acked this already. Either way:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v2 3/5] kasan, arm64: don't instrument functions that enable kasan

[Andrey Konovalov]

On Tue, Aug 4, 2020 at 3:19 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Tue, Aug 04, 2020 at 02:41:26PM +0200, Andrey Konovalov wrote:
> > This patch prepares Software Tag-Based KASAN for stack tagging support.
> >
> > With stack tagging enabled, KASAN tags stack variable in each function
> > in its prologue. In start_kernel() stack variables get tagged before KASAN
> > is enabled via setup_arch()->kasan_init(). As the result the tags for
> > start_kernel()'s stack variables end up in the temporary shadow memory.
> > Later when KASAN gets enabled, switched to normal shadow, and starts
> > checking tags, this leads to false-positive reports, as proper tags are
> > missing in normal shadow.
> >
> > Disable KASAN instrumentation for start_kernel(). Also disable it for
> > arm64's setup_arch() as a precaution (it doesn't have any stack variables
> > right now).
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> I thought I acked this already. Either way:
>
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Sorry, I forgot to include that into v2. Thanks!

[PATCH v2 4/5] kasan: allow enabling stack tagging for tag-based mode

[Andrey Konovalov]

Use CONFIG_KASAN_STACK to enable stack tagging.

Note, that HWASAN short granules [1] are disabled. Supporting those will
require more kernel changes.

[1] https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 scripts/Makefile.kasan | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 03757cc60e06..f4beee1b0013 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -44,7 +44,8 @@ else
 endif
 
 CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
-		-mllvm -hwasan-instrument-stack=0 \
+		-mllvm -hwasan-instrument-stack=$(CONFIG_KASAN_STACK) \
+		-mllvm -hwasan-use-short-granules=0 \
 		$(instrumentation_flags)
 
 endif # CONFIG_KASAN_SW_TAGS
-- 
2.28.0.163.g6104cc2f0b6-goog

[PATCH v2 5/5] kasan: adjust kasan_stack_oob for tag-based mode

[Andrey Konovalov]

Use OOB_TAG_OFF as access offset to land the access into the next granule.

Suggested-by: Walter Wu <walter-zh.wu@mediatek.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/test_kasan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 7674616d0c37..5d3f496893ef 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -488,7 +488,7 @@ static noinline void __init kasan_global_oob(void)
 static noinline void __init kasan_stack_oob(void)
 {
 	char stack_array[10];
-	volatile int i = 0;
+	volatile int i = OOB_TAG_OFF;
 	char *p = &stack_array[ARRAY_SIZE(stack_array) + i];
 
 	pr_info("out-of-bounds on stack\n");
-- 
2.28.0.163.g6104cc2f0b6-goog