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 4.16-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mm-do-not-forbid-_page_rw-before-init-for-__ro_after_init.patch
and it can be found in the queue-4.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Sun May 27 16:10:02 CEST 2018
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
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 <dave.hansen@xxxxxxxxxxxxxxx>
[ 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 <dave.hansen@xxxxxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/20180406205514.8D898241@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/pageattr.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -298,9 +298,11 @@ 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;
Patches currently in stable-queue which might be from dave.hansen@xxxxxxxxxxxxxxx are
queue-4.16/x86-mm-do-not-forbid-_page_rw-before-init-for-__ro_after_init.patch
