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From: matthieu castet on 12 Aug 2010 18:30
Hi,

because nobody seems to work on "NX protection for kernel data" patches [1], I decided to rework them a bit :
- remove unneeded alignment in vmlinux.lds
- call mark_nxdata_nx in mark_rodata_ro instead of free_initmem
- fix a bug in my machine where memory was x and rw after kernel data
- static_protections for bios rom is only enabled when CONFIG_PCI_BIOS (no x64)
- bios rom is set to x only when probing pcibios (this won't be done is mmconfig is supported).

A second patch is more radical : it make the ROM bios memory (0xe0000-0x100000) ro and x, but only for system
supporting NX (to avoid breaking very old machine). I don't know if it is safe.

I am waiting for your comment before reposting all the patches (module and improper large page preservation)
I only test it on a 32bit NX cpu.


Matthieu

[1]
Note: this patch depends on "Correct improper large page preservation" patch

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 script is adjusted so .text always starts and ends on a page bound
2. Linker script is adjusted so .rodata and .data always start and
end on a page boundary
3. void mark_nxdata_nx(void) added to arch/x86/mm/init.c with actual
functionality: NX is set for all pages from _etext through _end.
4. mark_nxdata_nx() called from free_initmem() (after init has been released
5. free_init_pages() sets released memory NX in arch/x86/mm/init.c

The results of patch application may be observed in the diff of kernel page
table dumps:
--- data_nx_pt_before.txt 2009-10-13 07:48:59.000000000 -0400
+++ data_nx_pt_after.txt 2009-10-13 07:26:46.000000000 -0400
@@ -2,8 +2,9 @@
0x00000000-0xc0000000 3G pmd
---[ Kernel Mapping ]---
0xc0000000-0xc0100000 1M RW GLB x pte
-0xc0100000-0xc048d000 3636K ro GLB x pte
-0xc048d000-0xc0600000 1484K RW GLB x pte
+0xc0100000-0xc0381000 2564K ro GLB x pte
+0xc0381000-0xc048d000 1072K ro GLB NX pte
+0xc048d000-0xc0600000 1484K RW GLB NX pte
0xc0600000-0xf7800000 882M RW PSE GLB NX pmd
0xf7800000-0xf79fe000 2040K RW GLB NX pte
0xf79fe000-0xf7a00000 8K pte

The patch have been developed for Linux 2.6.34-rc2 x86 by Siarhei Liakh
<sliakh.lkml(a)gmail.com> and Xuxian Jiang <jiang(a)cs.ncsu.edu>.

V1: initial patch for 2.6.30
V2: patch for 2.6.31-rc7
V3: moved all code into arch/x86, adjusted credits
V4: fixed ifdef, removed credits from CREDITS
V5: fixed an address calculation bug in mark_nxdata_nx()
V6: added acked-by and PT dump diff to commit log
V7: minor adjustments for -tip

Signed-off-by: Siarhei Liakh <sliakh.lkml(a)gmail.com>
Signed-off-by: Xuxian Jiang <jiang(a)cs.ncsu.edu>
Acked-by: Arjan van de Ven <arjan(a)linux.intel.com>
Reviewed-by: James Morris <jmorris(a)namei.org>
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