x86-32: tighten the bound on additional memory to map

Impact: Tighten bound to avoid masking errors

The definition of MAPPING_BEYOND_END was excessive; this has a nasty
tendency to mask bugs.  We have learned over time that this kind of
bug hiding can cause some very strange errors.  Therefore, tighten the
bound to only need to map the actual kernel area.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Yinghai Lu <yinghai@kernel.org>

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index fc884b90b6d25affd9fa2bf72e1007db19332bd9..30683883e0cdcf0bd669cb439206fefaf74301f2 100644 (file)
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -60,7 +60,8 @@
 #endif
 
 /* Enough space to fit pagetables for the low memory linear map */
-MAPPING_BEYOND_END = (PAGE_TABLE_SIZE(1 << (32 - PAGE_SHIFT)) * PAGE_SIZE)
+MAPPING_BEYOND_END = \
+       PAGE_TABLE_SIZE(((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT) << PAGE_SHIFT
 
 /*
  * Worst-case size of the kernel mapping we need to make: