linux-kernel - [PATCH 4.9 v2] x86/pti/efi: broken conversion from efi to kernel page table

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Message-Id: <20180115164414.19778-1-pasha.tatashin@oracle.com>
Date:   Mon, 15 Jan 2018 11:44:14 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     steven.sistare@...cle.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, gregkh@...uxfoundation.org, jkosina@...e.cz,
        hughd@...gle.com, dave.hansen@...ux.intel.com, luto@...nel.org,
        stable@...r.kernel.org
Subject: [PATCH 4.9 v2] x86/pti/efi: broken conversion from efi to kernel page table

The page table order must be increased for EFI table in order to avoid a
bug where NMI tries to change the page table to kernel page table, while
efi page table is active.

For more disccussion about this bug, see this thread:
http://lkml.iu.edu/hypermail/linux/kernel/1801.1/00951.html

Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
Reviewed-by: Steven Sistare <steven.sistare@...cle.com>
Acked-by: Jiri Kosina <jkosina@...e.cz>
---
 arch/x86/include/asm/pgalloc.h | 11 +++++++++++
 arch/x86/mm/pgtable.c          |  7 -------
 arch/x86/platform/efi/efi_64.c |  2 +-
 3 files changed, 12 insertions(+), 8 deletions(-)

Changelog:
	v1 - v2: Fixed compiling warning

diff --git a/arch/x86/include/asm/pgalloc.h b/arch/x86/include/asm/pgalloc.h
index b6d425999f99..1178a51b77f3 100644
--- a/arch/x86/include/asm/pgalloc.h
+++ b/arch/x86/include/asm/pgalloc.h
@@ -27,6 +27,17 @@ static inline void paravirt_release_pud(unsigned long pfn) {}
  */
 extern gfp_t __userpte_alloc_gfp;
 
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+/*
+ * Instead of one PGD, we acquire two PGDs.  Being order-1, it is
+ * both 8k in size and 8k-aligned.  That lets us just flip bit 12
+ * in a pointer to swap between the two 4k halves.
+ */
+#define PGD_ALLOCATION_ORDER 1
+#else
+#define PGD_ALLOCATION_ORDER 0
+#endif
+
 /*
  * Allocate and free page tables.
  */
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 5aaec8effc5f..209b9465e97a 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -345,13 +345,6 @@ static inline void _pgd_free(pgd_t *pgd)
 }
 #else
 
-/*
- * Instead of one pgd, Kaiser acquires two pgds.  Being order-1, it is
- * both 8k in size and 8k-aligned.  That lets us just flip bit 12
- * in a pointer to swap between the two 4k halves.
- */
-#define PGD_ALLOCATION_ORDER	kaiser_enabled
-
 static inline pgd_t *_pgd_alloc(void)
 {
 	return (pgd_t *)__get_free_pages(PGALLOC_GFP, PGD_ALLOCATION_ORDER);
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 2f25a363068c..dcb2d9d185a2 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -142,7 +142,7 @@ int __init efi_alloc_page_tables(void)
 		return 0;
 
 	gfp_mask = GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO;
-	efi_pgd = (pgd_t *)__get_free_page(gfp_mask);
+	efi_pgd = (pgd_t *)__get_free_pages(gfp_mask, PGD_ALLOCATION_ORDER);
 	if (!efi_pgd)
 		return -ENOMEM;
 
-- 
2.15.1