Re: + fully-honor-vdso_enabled.patch added to -mm tree

[Oleg Nesterov]

On 03/02, John Reiser wrote:
>
> Oleg Nesterov wrote:
> 
> > Still, I don't understand why we don't pass NEW_AUX_ENT(AT_SYSINFO) when
> > vdso_enabled == 0. We don't need linux-gate.so to use __kernel_vsyscall,
> > we have FIX_VDSO. In that case we should s/PAGE_KERNEL_RO/PAGE_READONLY/
> > of course. I guess the reason is some magic in glibc.
> 
> In the past there were problems where user code could not single-step
> (or even read the code of) such system calls.  Can these two operations
> be performed today with what you propose, particularly if FIX_VDSO is
> near 0xfffff000 ?

No, we can't COW the gate page, it lives in swapper_pg_dir. I am not sure
why we could not read it, we have gate_vma for that.

So, the reason is debugger. Thanks.

Oleg.

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