[PATCH] kasan: add no_sanitize attribute for clang builds

[PATCH] kasan: add no_sanitize attribute for clang builds

[Andrey Konovalov]

KASAN uses the __no_sanitize_address macro to disable instrumentation
of particular functions. Right now it's defined only for GCC build,
which causes false positives when clang is used.

This patch adds a definition for clang.

Note, that clang's revision 329612 or higher is required.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/compiler-clang.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index ceb96ecab96e..5a1d8580febe 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -25,6 +25,11 @@
 #define __SANITIZE_ADDRESS__
 #endif
 
+#ifdef CONFIG_KASAN
+#undef __no_sanitize_address
+#define __no_sanitize_address __attribute__((no_sanitize("address")))
+#endif
+
 /* Clang doesn't have a way to turn it off per-function, yet. */
 #ifdef __noretpoline
 #undef __noretpoline
-- 
2.17.0.484.g0c8726318c-goog

Re: [PATCH] kasan: add no_sanitize attribute for clang builds

[Andrey Ryabinin]

On 04/12/2018 08:29 PM, Andrey Konovalov wrote:
> KASAN uses the __no_sanitize_address macro to disable instrumentation
> of particular functions. Right now it's defined only for GCC build,
> which causes false positives when clang is used.
> 
> This patch adds a definition for clang.
> 
> Note, that clang's revision 329612 or higher is required.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  include/linux/compiler-clang.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index ceb96ecab96e..5a1d8580febe 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -25,6 +25,11 @@
>  #define __SANITIZE_ADDRESS__
>  #endif
>  
> +#ifdef CONFIG_KASAN

If, for whatever reason, developer decides to add __no_sanitize_address to some
generic function, guess what will happen next when he/she will try to build CONFIG_KASAN=n kernel?

> +#undef __no_sanitize_address
> +#define __no_sanitize_address __attribute__((no_sanitize("address")))
> +#endif
> +
>  /* Clang doesn't have a way to turn it off per-function, yet. */
>  #ifdef __noretpoline
>  #undef __noretpoline
> 

Re: [PATCH] kasan: add no_sanitize attribute for clang builds

[Andrey Konovalov]

On Fri, Apr 13, 2018 at 5:31 PM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
>
>
> On 04/12/2018 08:29 PM, Andrey Konovalov wrote:
>> KASAN uses the __no_sanitize_address macro to disable instrumentation
>> of particular functions. Right now it's defined only for GCC build,
>> which causes false positives when clang is used.
>>
>> This patch adds a definition for clang.
>>
>> Note, that clang's revision 329612 or higher is required.
>>
>> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>> ---
>>  include/linux/compiler-clang.h | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
>> index ceb96ecab96e..5a1d8580febe 100644
>> --- a/include/linux/compiler-clang.h
>> +++ b/include/linux/compiler-clang.h
>> @@ -25,6 +25,11 @@
>>  #define __SANITIZE_ADDRESS__
>>  #endif
>>
>> +#ifdef CONFIG_KASAN
>
> If, for whatever reason, developer decides to add __no_sanitize_address to some
> generic function, guess what will happen next when he/she will try to build CONFIG_KASAN=n kernel?

It's defined to nothing in compiler-gcc.h and redefined in
compiler-clang.h only if CONFIG_KASAN is enabled, so everything should
be fine. Am I missing something?

>
>> +#undef __no_sanitize_address
>> +#define __no_sanitize_address __attribute__((no_sanitize("address")))
>> +#endif
>> +
>>  /* Clang doesn't have a way to turn it off per-function, yet. */
>>  #ifdef __noretpoline
>>  #undef __noretpoline
>>

Re: [PATCH] kasan: add no_sanitize attribute for clang builds

[Andrey Ryabinin]

On 04/13/2018 08:34 PM, Andrey Konovalov wrote:
> On Fri, Apr 13, 2018 at 5:31 PM, Andrey Ryabinin
> <aryabinin@virtuozzo.com> wrote:
>>
>>
>> On 04/12/2018 08:29 PM, Andrey Konovalov wrote:
>>> KASAN uses the __no_sanitize_address macro to disable instrumentation
>>> of particular functions. Right now it's defined only for GCC build,
>>> which causes false positives when clang is used.
>>>
>>> This patch adds a definition for clang.
>>>
>>> Note, that clang's revision 329612 or higher is required.
>>>
>>> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>>> ---
>>>  include/linux/compiler-clang.h | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
>>> index ceb96ecab96e..5a1d8580febe 100644
>>> --- a/include/linux/compiler-clang.h
>>> +++ b/include/linux/compiler-clang.h
>>> @@ -25,6 +25,11 @@
>>>  #define __SANITIZE_ADDRESS__
>>>  #endif
>>>
>>> +#ifdef CONFIG_KASAN
>>
>> If, for whatever reason, developer decides to add __no_sanitize_address to some
>> generic function, guess what will happen next when he/she will try to build CONFIG_KASAN=n kernel?
> 
> It's defined to nothing in compiler-gcc.h and redefined in
> compiler-clang.h only if CONFIG_KASAN is enabled, so everything should
> be fine. Am I missing something?

No, It's was me missing something ;)
However, "#ifdef CONFIG_KASAN" seems to be redundant, I'd rather remove it.

Anyway:
	Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

Re: [PATCH] kasan: add no_sanitize attribute for clang builds

[Andrey Konovalov]

On Fri, Apr 13, 2018 at 9:16 PM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
> However, "#ifdef CONFIG_KASAN" seems to be redundant, I'd rather remove it.

Done, sent v2.

Thanks!