From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
The pageattr code has a pattern repeated where it sets _PAGE_GLOBAL
for present PTEs but clears it for non-present PTEs. The intention
is to keep _PAGE_GLOBAL from getting confused with _PAGE_PROTNONE
since _PAGE_GLOBAL is for present PTEs and _PAGE_PROTNONE is for
non-present
But, this pattern makes no sense. Effectively, it says, if you use
the pageattr code, always set _PAGE_GLOBAL when _PAGE_PRESENT.
canon_pgprot() will clear it if unsupported (because it masks the
value with __supported_pte_mask) but we *always* set it. Even if
canon_pgprot() did not filter _PAGE_GLOBAL, it would be OK.
_PAGE_GLOBAL is ignored when CR4.PGE=0 by the hardware.
This unconditional setting of _PAGE_GLOBAL is a problem when we have
PTI and non-PTI and we want some areas to have _PAGE_GLOBAL and some
not.
This updated version of the code says:
1. Clear _PAGE_GLOBAL when !_PAGE_PRESENT
2. Never set _PAGE_GLOBAL implicitly
3. Allow _PAGE_GLOBAL to be in cpa.set_mask
4. Allow _PAGE_GLOBAL to be inherited from previous PTE
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Nadav Amit <namit@xxxxxxxxxx>
---
b/arch/x86/mm/pageattr.c | 66 ++++++++++++++++-------------------------------
1 file changed, 23 insertions(+), 43 deletions(-)
diff -puN arch/x86/mm/pageattr.c~kpti-centralize-global-setting arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~kpti-centralize-global-setting 2018-04-06 10:47:53.651796130 -0700
+++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:53.655796130 -0700
@@ -512,6 +512,23 @@ static void __set_pmd_pte(pte_t *kpte, u
#endif
}
+static pgprot_t pgprot_clear_protnone_bits(pgprot_t prot)
+{
+ /*
+ * _PAGE_GLOBAL means "global page" for present PTEs.
+ * But, it is also used to indicate _PAGE_PROTNONE
+ * for non-present PTEs.
+ *
+ * This ensures that a _PAGE_GLOBAL PTE going from
+ * present to non-present is not confused as
+ * _PAGE_PROTNONE.
+ */
+ if (!(pgprot_val(prot) & _PAGE_PRESENT))
+ pgprot_val(prot) &= ~_PAGE_GLOBAL;
+
+ return prot;
+}
+
static int
try_preserve_large_page(pte_t *kpte, unsigned long address,
struct cpa_data *cpa)
@@ -577,18 +594,11 @@ try_preserve_large_page(pte_t *kpte, uns
* different bit positions in the two formats.
*/
req_prot = pgprot_4k_2_large(req_prot);
-
- /*
- * Set the PSE and GLOBAL flags only if the PRESENT flag is
- * set otherwise pmd_present/pmd_huge will return true even on
- * a non present pmd. The canon_pgprot will clear _PAGE_GLOBAL
- * for the ancient hardware that doesn't support it.
- */
+ req_prot = pgprot_clear_protnone_bits(req_prot);
if (pgprot_val(req_prot) & _PAGE_PRESENT)
- pgprot_val(req_prot) |= _PAGE_PSE | _PAGE_GLOBAL;
+ pgprot_val(req_prot) |= _PAGE_PSE;
else
- pgprot_val(req_prot) &= ~(_PAGE_PSE | _PAGE_GLOBAL);
-
+ pgprot_val(req_prot) &= ~_PAGE_PSE;
req_prot = canon_pgprot(req_prot);
/*
@@ -698,16 +708,7 @@ __split_large_page(struct cpa_data *cpa,
return 1;
}
- /*
- * Set the GLOBAL flags only if the PRESENT flag is set
- * otherwise pmd/pte_present will return true even on a non
- * present pmd/pte. The canon_pgprot will clear _PAGE_GLOBAL
- * for the ancient hardware that doesn't support it.
- */
- if (pgprot_val(ref_prot) & _PAGE_PRESENT)
- pgprot_val(ref_prot) |= _PAGE_GLOBAL;
- else
- pgprot_val(ref_prot) &= ~_PAGE_GLOBAL;
+ ref_prot = pgprot_clear_protnone_bits(ref_prot);
/*
* Get the target pfn from the original entry:
@@ -930,18 +931,7 @@ static void populate_pte(struct cpa_data
pte = pte_offset_kernel(pmd, start);
- /*
- * Set the GLOBAL flags only if the PRESENT flag is
- * set otherwise pte_present will return true even on
- * a non present pte. The canon_pgprot will clear
- * _PAGE_GLOBAL for the ancient hardware that doesn't
- * support it.
- */
- if (pgprot_val(pgprot) & _PAGE_PRESENT)
- pgprot_val(pgprot) |= _PAGE_GLOBAL;
- else
- pgprot_val(pgprot) &= ~_PAGE_GLOBAL;
-
+ pgprot = pgprot_clear_protnone_bits(pgprot);
pgprot = canon_pgprot(pgprot);
while (num_pages-- && start < end) {
@@ -1234,17 +1224,7 @@ repeat:
new_prot = static_protections(new_prot, address, pfn);
- /*
- * Set the GLOBAL flags only if the PRESENT flag is
- * set otherwise pte_present will return true even on
- * a non present pte. The canon_pgprot will clear
- * _PAGE_GLOBAL for the ancient hardware that doesn't
- * support it.
- */
- if (pgprot_val(new_prot) & _PAGE_PRESENT)
- pgprot_val(new_prot) |= _PAGE_GLOBAL;
- else
- pgprot_val(new_prot) &= ~_PAGE_GLOBAL;
+ new_prot = pgprot_clear_protnone_bits(new_prot);
/*
* We need to keep the pfn from the existing PTE,
_
