| Message ID | 20181102155710.2299475-1-arnd@arndb.de |
|---|---|
| State | New |
| Headers | show |
| Series | copy_{to,from}_user(): fix compile-time sanity checks with gcc -Og | expand |
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
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
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);
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(+) -- 2.18.0