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SubjectRe: [PATCH 2/6] kexec jump: check code size in control page
On Fri, Aug 08, 2008 at 10:44:37AM +0800, Huang Ying wrote:
> On Thu, 2008-08-07 at 22:31 +0200, Pavel Machek wrote:
> > Hi!
> >
> > > > PAGE_SIZE/2. This patch adds runtime checking for this.
> > > >
> > > > Signed-off-by: Huang Ying <ying.huang@intel.com>
> > ...
> >
> > > > {
> > > > if (nx_enabled)
> > > > set_pages_x(image->control_code_page, 1);
> > > > +
> > > > + BUG_ON((unsigned long)kexec_control_page_code_end - \
> > > > + (unsigned long)relocate_kernel >= PAGE_SIZE/2);
> > > > +
> > >
> >
> > > Run time check is better than nothing but I think in this case it would
> > > be better if we can catch it at compile time.
> > >
> > > One of the methods will be to write a small program of your own and
> > > put in script/ and at build time check for the size and flag error. May
> > > be there are other better ways to do this.
> >
> > BUILD_BUG_ON()?
>
> I tried with BUILD_BUG_ON(), and compiling is OK for both of following
> statement:
>
> BUILD_BUG_ON((unsigned long)kexec_control_page_code_end - \
> (unsigned long)relocate_kernel >= PAGE_SIZE/2);
>
> BUILD_BUG_ON((unsigned long)kexec_control_page_code_end - \
> (unsigned long)relocate_kernel < PAGE_SIZE/2);
>
> In general, I think value of kexec_control_page_code_end and
> relocate_kernel is not determined during compiling time. So
> BUILD_BUG_ON() doesn't work.
>
> Another idea, use ASSERT() command of ld link script as in the following
> patch:
>
> --- a/arch/x86/kernel/vmlinux_32.lds.S
> +++ b/arch/x86/kernel/vmlinux_32.lds.S
> @@ -209,3 +209,5 @@ SECTIONS
>
> DWARF_DEBUG
> }
> +
> +#include "vmlinux_check_32.lds.S"
> --- /dev/null
> +++ b/arch/x86/kernel/vmlinux_check_32.lds.S
> @@ -0,0 +1,3 @@
> +#include <asm/kexec.h>
> +
> +ASSERT(kexec_control_page_code_end - relocate_kernel >= 2048, "kexec control page code size is too big")
>
>

Use of ASSERT() looks good to me. I think creation of extra file for a
single ASSERT() can be avoided. Instead, we can just put this assert in
vmlinux_32.lds.S itself?

Thansk
Vivek


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