Re: [Fastboot] Re: [announce] kexec for linux 2.6.6

From: Eric W. Biederman
Date: Wed May 12 2004 - 12:01:37 EST

Ulrich Drepper <drepper@xxxxxxxxxx> writes:

> Eric W. Biederman wrote:
> > As a first draft we should be able to use the standard ELF mechanisms
> > for this. It is not like PIC shared libraries were new. Or is
> > there some specific problem you are thinking of with respect to
> > randomization?
> The official kernel does not have vdso randomization. Ingo has a patch
> for the Red Hat kernel which is used in the FC2 kernel. The patch
> effectively only changes the location at which the vdso is mapped. It
> does not change the vdso content. So the __kernel_vsyscall symbol in
> the vdso's symbol table is not changed.
> AT_SYSINFO is the right way to go forward but it is not directly
> accessible to userlevel code. And it is no pointer which will make
> architectures with function descriptors unhappy.

It sounds like the vdso just needs to be treated as a prelinked
vdso. You can find everything you need with AT_SYSINFO_EHDR.

In the case of function descriptors they should be in a data segment
that can get copied to another page, and corrected. Leaving the code
segment at it's randomized location.


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