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    SubjectRe: [PATCH] x86: NX protection for kernel data
    From
    On Sun, Jul 19, 2009 at 4:13 PM, Sam Ravnborg<sam@ravnborg.org> wrote:
    > On Sun, Jul 19, 2009 at 03:43:06PM -0400, Siarhei Liakh wrote:
    >> This patch expands functionality of CONFIG_DEBUG_RODATA to set main
    >> (static) kernel data area as NX.
    >> The following steps are taken to achieve this:
    >> 1. Linker scripts are adjusted so .text always starts and end on a page boundary
    >> 2. Linker scripts are adjusted so .rodata and .data always starts and
    >> end on a page boundary
    >> 3. void mark_nxdata_nx(void) added to arch/x86/mm/init_64.c and
    >> arch/x86/mm/init_32.c with actual functionality: NX is set for all
    >> pages from _etext through _edata
    >> 4. mark_nxdata_nx() called from init_post(void) in init/main.c
    >>
    >> The patch have been developed for Linux 2.6.30 x86 by Siarhei Liakh
    >> <sliakh.lkml@gmail.com> and Xuxian Jiang <jiang@cs.ncsu.edu>.
    >
    >
    > The patch no longer applies.
    > The file vmlinux_32.lds.S and vmlinux_64.lds.S has been unified
    > into one file.

    That is actually a great news. I will get the latest source and
    re-write the patch.

    >> --- a/arch/x86/kernel/vmlinux_32.lds.S
    >> +++ b/arch/x86/kernel/vmlinux_32.lds.S
    >> @@ -47,6 +47,7 @@ SECTIONS
    >>       IRQENTRY_TEXT
    >>       *(.fixup)
    >>       *(.gnu.warning)
    >> +     . = ALIGN(PAGE_SIZE);   /* .text should occupy whole number of pages */
    >>       _etext = .;                     /* End of text section */
    >
    > So _etext cover until page boundary - makes sense.
    >
    >>    } :text = 0x9090
    >>
    >> @@ -93,6 +94,7 @@ SECTIONS
    >>       *(.data.read_mostly)
    >>       _edata = .;             /* End of data section */
    >>    }
    >> +  . = ALIGN(PAGE_SIZE);              /* needed so we can set NX for .data */
    >
    > But here _edata does not cover until page boundary.
    > And alignmnet is located outside the output section
    > definition.
    > It would be better/more consistent to follow the style you use for .text here.

    You are correct. _edata should be the last thing in .data, and
    alignment should be done before it. However, this brings up a
    question: was there any specific reason to leave .data.init_task
    beyond the _edata? Should we move _edata into the the last of the
    .data.* sections to have poper view of kernel layout?
    --
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