Patch "x86/mm: Do not forbid _PAGE_RW before init for __ro_after_init" has been added to the 4.9-stable tree
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Greg Kroah-Hartman May 2, 2018, 6:16 p.m. UTC
This is a note to let you know that I've just added the patch titled

    x86/mm: Do not forbid _PAGE_RW before init for __ro_after_init

to the 4.9-stable tree which can be found at:;a=summary

The filename of the patch is:
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <> know about it.

From foo@baz Wed May  2 10:53:11 PDT 2018
From: Dave Hansen <>
Date: Fri, 6 Apr 2018 13:55:14 -0700
Subject: x86/mm: Do not forbid _PAGE_RW before init for __ro_after_init

From: Dave Hansen <>

[ Upstream commit 639d6aafe437a7464399d2a77d006049053df06f ]

__ro_after_init data gets stuck in the .rodata section.  That's normally
fine because the kernel itself manages the R/W properties.

But, if we run __change_page_attr() on an area which is __ro_after_init,
the .rodata checks will trigger and force the area to be immediately
read-only, even if it is early-ish in boot.  This caused problems when
trying to clear the _PAGE_GLOBAL bit for these area in the PTI code:
it cleared _PAGE_GLOBAL like I asked, but also took it up on itself
to clear _PAGE_RW.  The kernel then oopses the next time it wrote to
a __ro_after_init data structure.

To fix this, add the kernel_set_to_readonly check, just like we have
for kernel text, just a few lines below in this function.

Signed-off-by: Dave Hansen <>
Acked-by: Kees Cook <>
Cc: Andrea Arcangeli <>
Cc: Andy Lutomirski <>
Cc: Arjan van de Ven <>
Cc: Borislav Petkov <>
Cc: Dan Williams <>
Cc: David Woodhouse <>
Cc: Greg Kroah-Hartman <>
Cc: Hugh Dickins <>
Cc: Josh Poimboeuf <>
Cc: Juergen Gross <>
Cc: Linus Torvalds <>
Cc: Nadav Amit <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Sasha Levin <>
Signed-off-by: Greg Kroah-Hartman <>
 arch/x86/mm/pageattr.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patches currently in stable-queue which might be from are


diff mbox

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -279,9 +279,11 @@  static inline pgprot_t static_protection
 	 * The .rodata section needs to be read-only. Using the pfn
-	 * catches all aliases.
+	 * catches all aliases.  This also includes __ro_after_init,
+	 * so do not enforce until kernel_set_to_readonly is true.
-	if (within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT,
+	if (kernel_set_to_readonly &&
+	    within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT,
 		   __pa_symbol(__end_rodata) >> PAGE_SHIFT))
 		pgprot_val(forbidden) |= _PAGE_RW;