Patch "x86/mm: Fix overlap of i386 CPU_ENTRY_AREA with FIX_BTMAP" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

x86/mm: Fix overlap of i386 CPU_ENTRY_AREA with FIX_BTMAP

to the 4.14-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:

     x86mm_Fix_overlap_of_i386_CPU_ENTRY_AREA_with_FIX_BTMAP.patch

and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Subject: x86/mm: Fix overlap of i386 CPU_ENTRY_AREA with FIX_BTMAP
From: William Grant [email protected]
Date: Tue Jan 30 22:22:55 2018 +1100

From: William Grant [email protected]

commit 55f49fcb879fbeebf2a8c1ac7c9e6d90df55f798

Since commit 92a0f81d8957 ("x86/cpu_entry_area: Move it out of the fixmap"), i386's CPU_ENTRY_AREA has been mapped to the memory area just below FIXADDR_START. But already immediately before FIXADDR_START is the FIX_BTMAP area, which means that early_ioremap can collide with the entry area.

It's especially bad on PAE where FIX_BTMAP_BEGIN gets aligned to exactly match CPU_ENTRY_AREA_BASE, so the first early_ioremap slot clobbers the IDT and causes interrupts during early boot to reset the system.

The overlap wasn't a problem before the CPU entry area was introduced, as the fixmap has classically been preceded by the pkmap or vmalloc areas, neither of which is used until early_ioremap is out of the picture.

Relocate CPU_ENTRY_AREA to below FIX_BTMAP, not just below the permanent fixmap area.

---
 arch/x86/include/asm/fixmap.h           |    6 ++++--
 arch/x86/include/asm/pgtable_32_types.h |    5 +++--
 2 files changed, 7 insertions(+), 4 deletions(-)

@@ -137,8 +137,10 @@ enum fixed_addresses {
 
 extern void reserve_top_address(unsigned long reserve);
 
-#define FIXADDR_SIZE	(__end_of_permanent_fixed_addresses << PAGE_SHIFT)
-#define FIXADDR_START	(FIXADDR_TOP - FIXADDR_SIZE)
+#define FIXADDR_SIZE		(__end_of_permanent_fixed_addresses << PAGE_SHIFT)
+#define FIXADDR_START		(FIXADDR_TOP - FIXADDR_SIZE)
+#define FIXADDR_TOT_SIZE	(__end_of_fixed_addresses << PAGE_SHIFT)
+#define FIXADDR_TOT_START	(FIXADDR_TOP - FIXADDR_TOT_SIZE)
 
 extern int fixmaps_set;
 

@@ -44,8 +44,9 @@ extern bool __vmalloc_start_set; /* set
  */
 #define CPU_ENTRY_AREA_PAGES	(NR_CPUS * 40)
 
-#define CPU_ENTRY_AREA_BASE				\
-	((FIXADDR_START - PAGE_SIZE * (CPU_ENTRY_AREA_PAGES + 1)) & PMD_MASK)
+#define CPU_ENTRY_AREA_BASE						\
+	((FIXADDR_TOT_START - PAGE_SIZE * (CPU_ENTRY_AREA_PAGES + 1))   \
+	 & PMD_MASK)
 
 #define PKMAP_BASE		\
 	((CPU_ENTRY_AREA_BASE - PAGE_SIZE) & PMD_MASK)

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/x86mm_Fix_overlap_of_i386_CPU_ENTRY_AREA_with_FIX_BTMAP.patch