Revert "Move xen patchset to new version's subdir."

[people/pmueller/ipfire-2.x.git] / src / patches / suse-2.6.27.25 / patches.arch / x86-pageattr-pmd-permission-fix.patch

diff --git a/src/patches/suse-2.6.27.25/patches.arch/x86-pageattr-pmd-permission-fix.patch b/src/patches/suse-2.6.27.25/patches.arch/x86-pageattr-pmd-permission-fix.patch
new file mode 100644 (file)
index 0000000..4238fa7
--- /dev/null
+++ b/src/patches/suse-2.6.27.25/patches.arch/x86-pageattr-pmd-permission-fix.patch
@@ -0,0 +1,75 @@
+From: Ingo Molnar <mingo@elte.hu>
+References: bnc#439348
+Subject: x86: use the right protections for split-up pagetables
+Patch-mainline: yes
+Git: 07a66d7c53a538e1a9759954a82bb6c07365eff9
+    
+    Steven Rostedt found a bug in where in his modified kernel
+    ftrace was unable to modify the kernel text, due to the PMD
+    itself having been marked read-only as well in
+    split_large_page().
+    
+    The fix, suggested by Linus, is to not try to 'clone' the
+    reference protection of a huge-page, but to use the standard
+    (and permissive) page protection bits of KERNPG_TABLE.
+    
+    The 'cloning' makes sense for the ptes but it's a confused and
+    incorrect concept at the page table level - because the
+    pagetable entry is a set of all ptes and hence cannot
+    'clone' any single protection attribute - the ptes can be any
+    mixture of protections.
+    
+    With the permissive KERNPG_TABLE, even if the pte protections
+    get changed after this point (due to ftrace doing code-patching
+    or other similar activities like kprobes), the resulting combined
+    protections will still be correct and the pte's restrictive
+    (or permissive) protections will control it.
+    
+    Also update the comment.
+    
+    This bug was there for a long time but has not caused visible
+    problems before as it needs a rather large read-only area to
+    trigger. Steve possibly hacked his kernel with some really
+    large arrays or so. Anyway, the bug is definitely worth fixing.
+    
+    [ Huang Ying also experienced problems in this area when writing
+      the EFI code, but the real bug in split_large_page() was not
+      realized back then. ]
+    
+    Reported-by: Steven Rostedt <rostedt@goodmis.org>
+    Reported-by: Huang Ying <ying.huang@intel.com>
+    Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
+    Signed-off-by: Ingo Molnar <mingo@elte.hu>
+
+Acked-by: Nick Piggin <npiggin@suse.de>
+
+---
+ arch/x86/mm/pageattr.c |   15 +++++----------
+ 1 file changed, 5 insertions(+), 10 deletions(-)
+
+--- a/arch/x86/mm/pageattr.c
++++ b/arch/x86/mm/pageattr.c
+@@ -557,18 +557,13 @@ static int split_large_page(pte_t *kpte,
+ #endif
+ 
+       /*
+-       * Install the new, split up pagetable. Important details here:
++       * Install the new, split up pagetable.
+        *
+-       * On Intel the NX bit of all levels must be cleared to make a
+-       * page executable. See section 4.13.2 of Intel 64 and IA-32
+-       * Architectures Software Developer's Manual).
+-       *
+-       * Mark the entry present. The current mapping might be
+-       * set to not present, which we preserved above.
++       * We use the standard kernel pagetable protections for the new
++       * pagetable protections, the actual ptes set above control the
++       * primary protection behavior:
+        */
+-      ref_prot = pte_pgprot(pte_mkexec(pte_clrhuge(*kpte)));
+-      pgprot_val(ref_prot) |= _PAGE_PRESENT;
+-      __set_pmd_pte(kpte, address, mk_pte(base, ref_prot));
++      __set_pmd_pte(kpte, address, mk_pte(base, __pgprot(_KERNPG_TABLE)));
+ 
+       /*
+        * Intel Atom errata AAH41 workaround.