* [PATCH] copy_{to,from}_user(): fix compile-time sanity checks with gcc -Og
@ 2018-11-02 15:56 Arnd Bergmann
2018-11-03 0:03 ` Changbin Du
0 siblings, 1 reply; 3+ messages in thread
From: Arnd Bergmann @ 2018-11-02 15:56 UTC (permalink / raw)
To: Andrew Morton
Cc: Masahiro Yamada, Al Viro, Arnd Bergmann, Changbin Du,
Marc Zyngier, Alex Bennée, Dave Martin, Kees Cook, Levin,
Alexander (Sasha Levin),
linux-kernel
When CONFIG_CC_OPTIMIZE_FOR_DEBUGGING is set, we get countless warnings
like
In function 'check_copy_size',
inlined from 'copy_from_user' at include/linux/uaccess.h:146:6,
inlined from '__copy_siginfo_from_user' at kernel/signal.c:3032:6:
include/linux/thread_info.h:147:4: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
It seems that constant propagation doesn't work well enough to make
this code reliable, so turn it off for that configuration.
Cc: Changbin Du<changbin.du@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
include/linux/thread_info.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 8d8821b3689a..762f379bdf5d 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -138,6 +138,11 @@ static __always_inline bool
check_copy_size(const void *addr, size_t bytes, bool is_source)
{
int sz = __compiletime_object_size(addr);
+
+ /* constant propagation doesn't work well with -Og */
+ if (IS_ENABLED(CONFIG_CC_OPTIMIZE_FOR_DEBUGGING))
+ return true;
+
if (unlikely(sz >= 0 && sz < bytes)) {
if (!__builtin_constant_p(bytes))
copy_overflow(sz, bytes);
--
2.18.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] copy_{to,from}_user(): fix compile-time sanity checks with gcc -Og
2018-11-02 15:56 [PATCH] copy_{to,from}_user(): fix compile-time sanity checks with gcc -Og Arnd Bergmann
@ 2018-11-03 0:03 ` Changbin Du
2018-11-03 15:46 ` Arnd Bergmann
0 siblings, 1 reply; 3+ messages in thread
From: Changbin Du @ 2018-11-03 0:03 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Andrew Morton, Masahiro Yamada, Al Viro, Changbin Du,
Marc Zyngier, Alex Bennée, Dave Martin, Kees Cook, Levin,
Alexander (Sasha Levin),
linux-kernel
On Fri, Nov 02, 2018 at 04:56:58PM +0100, Arnd Bergmann wrote:
> When CONFIG_CC_OPTIMIZE_FOR_DEBUGGING is set, we get countless warnings
> like
>
> In function 'check_copy_size',
> inlined from 'copy_from_user' at include/linux/uaccess.h:146:6,
> inlined from '__copy_siginfo_from_user' at kernel/signal.c:3032:6:
> include/linux/thread_info.h:147:4: error: call to '__bad_copy_to' declared with attribute error: copy destination size is too small
>
> It seems that constant propagation doesn't work well enough to make
> this code reliable, so turn it off for that configuration.
>
This is caused by __compiletime_warning() and fixed by below change
already. Could you try the latest kbuild tree?
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -86,8 +86,10 @@
#define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
#ifndef __CHECKER__
+#ifndef CONFIG_CC_OPTIMIZE_FOR_DEBUGGING
#define __compiletime_warning(message) __attribute__((warning(message)))
#define __compiletime_error(message) __attribute__((error(message)))
+#endif
> Cc: Changbin Du<changbin.du@gmail.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> include/linux/thread_info.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index 8d8821b3689a..762f379bdf5d 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -138,6 +138,11 @@ static __always_inline bool
> check_copy_size(const void *addr, size_t bytes, bool is_source)
> {
> int sz = __compiletime_object_size(addr);
> +
> + /* constant propagation doesn't work well with -Og */
> + if (IS_ENABLED(CONFIG_CC_OPTIMIZE_FOR_DEBUGGING))
> + return true;
> +
> if (unlikely(sz >= 0 && sz < bytes)) {
> if (!__builtin_constant_p(bytes))
> copy_overflow(sz, bytes);
> --
> 2.18.0
>
--
Thanks,
Changbin Du
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] copy_{to,from}_user(): fix compile-time sanity checks with gcc -Og
2018-11-03 0:03 ` Changbin Du
@ 2018-11-03 15:46 ` Arnd Bergmann
0 siblings, 0 replies; 3+ messages in thread
From: Arnd Bergmann @ 2018-11-03 15:46 UTC (permalink / raw)
To: Changbin Du
Cc: Andrew Morton, Masahiro Yamada, Al Viro, Marc Zyngier,
Alex Bennée, Dave Martin, Kees Cook, Levin,
Alexander (Sasha Levin),
linux-kernel
On 11/3/18, Changbin Du <changbin.du@gmail.com> wrote:
> On Fri, Nov 02, 2018 at 04:56:58PM +0100, Arnd Bergmann wrote:
>> When CONFIG_CC_OPTIMIZE_FOR_DEBUGGING is set, we get countless warnings
>> like
>>
>> In function 'check_copy_size',
>> inlined from 'copy_from_user' at include/linux/uaccess.h:146:6,
>> inlined from '__copy_siginfo_from_user' at kernel/signal.c:3032:6:
>> include/linux/thread_info.h:147:4: error: call to '__bad_copy_to' declared
>> with attribute error: copy destination size is too small
>>
>> It seems that constant propagation doesn't work well enough to make
>> this code reliable, so turn it off for that configuration.
>>
> This is caused by __compiletime_warning() and fixed by below change
> already. Could you try the latest kbuild tree?
>
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -86,8 +86,10 @@
> #define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
>
> #ifndef __CHECKER__
> +#ifndef CONFIG_CC_OPTIMIZE_FOR_DEBUGGING
> #define __compiletime_warning(message) __attribute__((warning(message)))
> #define __compiletime_error(message) __attribute__((error(message)))
> +#endif
Right, that works as well, but my version is a bit less invasive as it
only disables the __compiletime_error in the one file that introduced
the regression, and not all of them. I have built hundreds of randconfig
builds and found no other problem with __compiletime_error(), though
I did find a bunch of (correct) section mismatch warnings and
false-positive -Wformat-overflow= warnings with
CONFIG_CC_OPTIMIZE_FOR_DEBUGGING (patches pending).
I also got some link errors for which I already posted patches.
Arnd
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2018-11-02 15:56 [PATCH] copy_{to,from}_user(): fix compile-time sanity checks with gcc -Og Arnd Bergmann
2018-11-03 0:03 ` Changbin Du
2018-11-03 15:46 ` Arnd Bergmann
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