Messages in this thread | | | Date | Sat, 3 Mar 2007 01:18:54 +0300 | From | Oleg Nesterov <> | Subject | Re: + fully-honor-vdso_enabled.patch added to -mm tree |
| |
On 03/02, John Reiser wrote: > > Oleg Nesterov wrote: > > John Reiser wrote: > > >>+ switch (vdso_enabled) { > >>+ case 0: /* none */ > >>+ return 0; > > > > > > This means we don't initialize mm->context.vdso and ->sysenter_return. > > > > Is it ok? For example, setup_rt_frame() uses VDSO_SYM(&__kernel_rt_sigreturn), > > sysenter_past_esp pushes ->sysenter_return on stack. > > Paul Mundt has commented on setup_rt_frame() and provided a patch which > bullet-proofs that area. I will include that patch into the next revision.
Confused. I still think his patch incomplete. Don't we need the same check in setup_rt_frame() ?
> The value of ->sysenter_return is interpreted in user space by the > sysexit instruction; nobody else cares what the value is. The kernel > is not required to provide a good value when vdso_enabled is zero,
Yes sure.
> Both context.vdso and sysenter_return could be set to zero whenever > vdso_enabled is zero; those two values might even be defaulted. > I'll add such a change to the next revision of the patch, if you'll > defend it against claims of "unnecessary code."
context.vdso == NULL after mm_alloc(). I don't see a "good" arch dependent function to clear ->sysenter_return (if we really need this). May be flush_thread().
> > Note also that load_elf_binary does > > > > arch_setup_additional_pages() > > create_elf_tables() > > > > , looks like application can crash after exec if vdso_enabled changes from 0 > > to 1 in between. > > Correct. Changing vdso_enabled from 0 to non-zero must be prepared > to lose this race if it is not prevented. Ordinarily it won't matter > because the administrator will perform such changes at a "quiet" time.
I agree, this problem is mostly theoretical, but I believe it is hardly possible to document what the "quiet" time is ;)
How about
#define ARCH_DLINFO -do if (vdso_enabled) { +do if (VDSO_BASE) { ?
Oleg.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |