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Subject[PATCH] [1/5] CPA: Split static_protections into required_static_prot and advised_static_prot
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There is a big difference between NX and RO. NX absolutely has to be cleared
or the kernel will fail while RO just can be set, but does not need to.
And for a large page area not setting NX if there is a area below
it that needs it is essential, while making it ro is optional again.

This is needed for a followup patch who uses requred_static_prot() for large
pages where it is inconvenient to check all pages.

No behaviour change in this patch.

[Lines > 80 characters are changed in followup patch]
Signed-off-by: Andi Kleen <ak@suse.de>

---
arch/x86/mm/pageattr.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
Index: linux/arch/x86/mm/pageattr.c
===================================================================
--- linux.orig/arch/x86/mm/pageattr.c
+++ linux/arch/x86/mm/pageattr.c
@@ -149,7 +149,7 @@ static unsigned long virt_to_highmap(voi
* right (again, ioremap() on BIOS memory is not uncommon) so this function
* checks and fixes these known static required protection bits.
*/
-static inline pgprot_t static_protections(pgprot_t prot, unsigned long address)
+static inline pgprot_t required_static_prot(pgprot_t prot, unsigned long address)
{
pgprot_t forbidden = __pgprot(0);

@@ -173,21 +173,25 @@ static inline pgprot_t static_protection
pgprot_val(forbidden) |= _PAGE_NX;


+ prot = __pgprot(pgprot_val(prot) & ~pgprot_val(forbidden));
+
+ return prot;
+}
+
+static inline pgprot_t advised_static_prot(pgprot_t prot, unsigned long address)
+{
#ifdef CONFIG_DEBUG_RODATA
/* The .rodata section needs to be read-only */
if (within(address, (unsigned long)__start_rodata,
(unsigned long)__end_rodata))
- pgprot_val(forbidden) |= _PAGE_RW;
+ pgprot_val(prot) &= ~_PAGE_RW;
/*
* Do the same for the x86-64 high kernel mapping
*/
if (within(address, virt_to_highmap(__start_rodata),
virt_to_highmap(__end_rodata)))
- pgprot_val(forbidden) |= _PAGE_RW;
+ pgprot_val(prot) &= ~_PAGE_RW;
#endif
-
- prot = __pgprot(pgprot_val(prot) & ~pgprot_val(forbidden));
-
return prot;
}

@@ -318,7 +322,8 @@ try_preserve_large_page(pte_t *kpte, uns

pgprot_val(new_prot) &= ~pgprot_val(cpa->mask_clr);
pgprot_val(new_prot) |= pgprot_val(cpa->mask_set);
- new_prot = static_protections(new_prot, address);
+ new_prot = required_static_prot(new_prot, address);
+ new_prot = advised_static_prot(new_prot, address);

/*
* If there are no changes, return. maxpages has been updated
@@ -456,7 +461,8 @@ repeat:
pgprot_val(new_prot) &= ~pgprot_val(cpa->mask_clr);
pgprot_val(new_prot) |= pgprot_val(cpa->mask_set);

- new_prot = static_protections(new_prot, address);
+ new_prot = required_static_prot(new_prot, address);
+ new_prot = advised_static_prot(new_prot, address);

/*
* We need to keep the pfn from the existing PTE,
@@ -546,7 +552,7 @@ static int change_page_attr_addr(struct
* for the non obvious details.
*
* Note that NX and other required permissions are
- * checked in static_protections().
+ * checked in required_static_prot().
*/
address = phys_addr + HIGH_MAP_START - phys_base;


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