Re: [PATCH] mm: provide a fallback for PAGE_KERNEL_RO for architectures

From: Matthew Wilcox
Date: Fri Apr 27 2018 - 23:18:22 EST

On Fri, Apr 27, 2018 at 05:15:26PM -0700, Luis R. Rodriguez wrote:
> Some architectures do not define PAGE_KERNEL_RO, best we can do
> for them is to provide a fallback onto PAGE_KERNEL. Remove the
> hack from the firmware loader and move it onto the asm-generic
> header, and document while at it the affected architectures
> which do not have a PAGE_KERNEL_RO:
> o alpha
> o ia64
> o m68k
> o mips
> o sparc64
> o sparc

ia64 doesn't have it?

*fx: riffles through architecture book*

That seems like an oversight of the Linux port. Tony, Fenghua, any thoughts?

(also, Luis, maybe move the PAGE_KERNEL_EXEC fallback the same way you
moved the PAGE_KERNEL_RO fallback?)

--- >8 ---


The rest of the kernel was falling back to simple PAGE_KERNEL pages; using
PAGE_KERNEL_RO and PAGE_KERNEL_EXEC provide better protection against
unintended writes.

Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>

diff --git a/arch/ia64/include/asm/pgtable.h b/arch/ia64/include/asm/pgtable.h
index 165827774bea..041a32a7960d 100644
--- a/arch/ia64/include/asm/pgtable.h
+++ b/arch/ia64/include/asm/pgtable.h
@@ -23,7 +23,7 @@

* First, define the various bits in a PTE. Note that the PTE format
- * matches the VHPT short format, the firt doubleword of the VHPD long
+ * matches the VHPT short format, the first doubleword of the VHPD long
* format, and the first doubleword of the TLB insertion format.
#define _PAGE_P_BIT 0
@@ -142,9 +142,11 @@
#define PAGE_COPY_EXEC __pgprot(__ACCESS_BITS | _PAGE_PL_3 | _PAGE_AR_RX)
#define PAGE_GATE __pgprot(__ACCESS_BITS | _PAGE_PL_0 | _PAGE_AR_X_RX)
#define PAGE_KERNEL __pgprot(__DIRTY_BITS | _PAGE_PL_0 | _PAGE_AR_RWX)
-#define PAGE_KERNELRX __pgprot(__ACCESS_BITS | _PAGE_PL_0 | _PAGE_AR_RX)
+#define PAGE_KERNEL_RO __pgprot(__ACCESS_BITS | _PAGE_PL_0 | _PAGE_AR_R)
+#define PAGE_KERNEL_RX __pgprot(__ACCESS_BITS | _PAGE_PL_0 | _PAGE_AR_RX)
#define PAGE_KERNEL_UC __pgprot(__DIRTY_BITS | _PAGE_PL_0 | _PAGE_AR_RWX | \

# ifndef __ASSEMBLY__