--- En date de : Jeu 26.11.09, Mulyadi Santosa <mulyadi.sant...@gmail.com> a écrit :
> De: Mulyadi Santosa <mulyadi.sant...@gmail.com> > Objet: Re: Overwriting sys_call_table entries > À: flone...@etud.insa-toulouse.fr > Cc: kernelnewbies@nl.linux.org > Date: Jeudi 26 Novembre 2009, 13h51 > On Thu, Nov 26, 2009 at 6:31 AM, > Fernand LONE SANG <flone...@yahoo.com> > wrote: > > As a consequence, I override the permissions to access > to the sys_call_table entries and made them writable using a > lkm. After setting the needed permissions on the page, when > I overwrite an entry of the sys_call_table, my system hangs > (No kernel oops, my system simply freezes). > > AFAIK there is no lock that protect modification toward > sys_call_table. As the consequence, you might overwrite the > system > call entry while it was currently referenced. > > Actually, IMO, even on 2.4, loosely replacing certain or > all > sys_call_table entries are highly discouraged. The reason > is > similar...you don't know whether they are currently > referenced or not, > right? I finally found why my lkm froze when i try to change the sys_call_table entries. Actually, i forgot to change the page directory attributes. You're right when saying That changing a syscall is discouraged. But for what i do on my PC, concurrent access is not really a problem. > Well, maybe you might get better chance if you do it via > atomic > assembly instruction (i.e the one that can swap values > stored between > two memory region), but still, I am not whether it's the > answer to > your problem. > > -- > regards, > > Mulyadi Santosa > Freelance Linux trainer and consultant > > blog: the-hydra.blogspot.com > training: mulyaditraining.blogspot.com > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecar...@nl.linux.org Please read the FAQ at http://kernelnewbies.org/FAQ
