[PATCH 0/3] Make kexec work with CONFIG_DEBUG_RODATA enabled

[Nikolay Borisov]

> From: Will Deacon [mailto:will.deacon at arm.com]
> Hi Nikolay,
>
> On Mon, Apr 28, 2014 at 10:31:44AM +0100, Nikolay Borisov wrote:
> > This patch makes kexec work on a kernel that has its .text section
> set to read
> > only. The main reason of doing it is because there is a patch in the
> making
> > (http://lists.infradead.org/pipermail/linux-arm-kernel/2014-
> April/244779.html)
> > which aims to make it possible to flag the kernel's code section as
> read-only,
> > rendering kexec inoperable.
> >
> > The first patch does the actual functional changes while the 2nd one
> is
> > optional and is only to be used in case you have already applied the
> aforementioned
> > CONFIG_DEBUG_RODATA patch
> >
> > Patch 3 is also optional and tries to make the assembly code a bit
> more "sane"
> > by introducing a .struct to describe the parameters for the kernel
> relocation
> > stub.
> >
> > Those patches have been tested on linux 3.14 on THUMB-2/non-THUMB-2
> host
> > kernels.
> >
> > Patch 1 and 3 apply cleanly on 3.15-rc3 and Patch 2 applies cleanly,
> provided
> > that Kees' patch is applied as well.
> >
> > Kees also managed to test that on a QEMU 2.0 based machine.
>
> Wouldn't it be far simpler to set_kernel_text_rw() on a kexec? At this
> point, we've committed to replacing our image, so whether we can write
> to the .text of the old image before we clobber it entirely seems somewhat
> moot to me.
>

We are poking one of the values in the prepare stage so doing set_kernel_text_rw() there
won't be very clean solution. However, I agree that if the values being poked into the prep
stage is stashed in a static variable and then in the kexec_execute function we make the kernel
RW since we are turning the MMO off and nuking the old kernel anyway.

> Will

Regards,
Nikolay

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