Messages in this thread | | | Subject | Re: [PATCH] powerpc/mm: Only read faulting instruction when necessary in do_page_fault() | From | Christophe LEROY <> | Date | Mon, 24 Apr 2017 12:26:11 +0200 |
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Le 24/04/2017 à 11:15, Michael Ellerman a écrit : > Christophe Leroy <christophe.leroy@c-s.fr> writes: > >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c >> index 400f2d0d42f8..3d506589236c 100644 >> --- a/arch/powerpc/mm/fault.c >> +++ b/arch/powerpc/mm/fault.c >> @@ -356,8 +348,22 @@ int do_page_fault(struct pt_regs *regs, unsigned long address, >> * between the last mapped region and the stack will >> * expand the stack rather than segfaulting. >> */ >> - if (address + 2048 < uregs->gpr[1] && !store_updates_sp(inst)) >> - goto bad_area; >> + if (address + 2048 < uregs->gpr[1]) { >> + if (!inst) { > > That looks like it could lead to an infinite loop, if the instruction > that caused the fault has been overwritten with NULL by another thread.
If the inst is NULL, store_updates_sp(inst) returns false so it jumps to bad_area_nosemaphore
Christophe
> > Or did I miss something? (I only read the diff) > >> + /* >> + * We want to do this outside mmap_sem, because >> + * reading code around nip can result in fault, >> + * which will cause a deadlock when called with >> + * mmap_sem held >> + */ >> + up_read(&mm->mmap_sem); >> + __get_user(inst, >> + (unsigned int __user *)regs->nip); >> + if (!store_updates_sp(inst)) >> + goto bad_area_nosemaphore; >> + goto retry; >> + } > > > cheers >
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