Messages in this thread | | | Subject | Re: [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault() | From | Christophe LEROY <> | Date | Fri, 2 Jun 2017 11:39:23 +0200 |
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Le 02/06/2017 à 11:26, Michael Ellerman a écrit : > Christophe Leroy <christophe.leroy@c-s.fr> writes: > >> Only the get_user() in store_updates_sp() has to be done outside >> the mm semaphore. All the comparison can be done within the semaphore, >> so only when really needed. >> >> As we got a DSI exception, the address pointed by regs->nip is >> obviously valid, otherwise we would have had a instruction exception. >> So __get_user() can be used instead of get_user() > > I don't think that part is true. > > You took a DSI so there *was* an instruction at NIP, but since then it > may have been unmapped by another thread. > > So I don't think you can assume the get_user() will succeed. >
The difference between get_user() and __get_user() is that get_user() performs an access_ok() in addition.
Doesn't access_ok() only checks whether addr is below TASK_SIZE to ensure it is a valid user address ?
Christophe
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