On Sunday 27 February 2011, Guan Xuetao wrote: > > -----Original Message----- > > From: Arnd Bergmann [mailto:arnd@xxxxxxxx] > > Sent: Friday, February 18, 2011 1:45 AM > > To: Guan Xuetao > > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-arch@xxxxxxxxxxxxxxx; 'Greg KH' > > Subject: Re: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess > > > > On Wednesday 16 February 2011, Guan Xuetao wrote: > > > + > > > +#define __kernel_ok (segment_eq(get_fs(), KERNEL_DS)) > > > +#define __user_ok(addr, size) (((size) <= TASK_SIZE) \ > > > + && ((addr) <= TASK_SIZE - (size))) > > > +#define __access_ok(addr, size) (__kernel_ok || __user_ok((addr), (size))) > > > > A nice trick to simplify this is to introduce a per-process variable for comparing > > the pointer, set_fs() then sets this variable to either TASK_SIZE or > > UINT_MAX. > > Perhaps like this: > 1. add a member named kaddr in thread_info > 2. add following assignment codes in set_fs: > current_thread_info()->kaddr = segment_eq(fs, KERNEL_DS) ? UINT_MAX : TASK_SIZE; > 3. then __access_ok will be: > #define addr > #define __access_ok(addr, size) (((size) <= TASK_SIZE) \ > && ((addr) <= current_thread_info()->kaddr) - (size))) That would also work. What I meant was to have #define set_fs(fs) \ do { current_thread_info()->kaddr = (fs); } while (0) #define KERNEL_DS UINT_MAX #define USER_DS TASK_SIZE Either way is fine with me, just choose whichever works best for you in terms of code size. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
