[PATCH v3 1/2] kaslr: shift linear region randomization ahead of memory_limit

[pierre Kuo <vichy.kuo@gmail.com>]

The following is schematic diagram of the program before and after the
modification.

Before:
if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) {} --(a)
if (memory_limit != PHYS_ADDR_MAX) {}                               --(b)
if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) {}       --(c)
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {}                           --(d)*

After:
if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) {} --(a)
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {}                           --(d)*
if (memory_limit != PHYS_ADDR_MAX) {}                               --(b)
if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) {}       --(c)

After grouping modification of memstart_address by moving linear region
randomization ahead of memory_init, driver can safely using macro,
__phys_to_virt, in (b) or (c), if necessary.

Signed-off-by: pierre Kuo <vichy.kuo@gmail.com>
---
Changes in v2:
- add Fixes tag

Changes in v3:
- adding patch of shifting linear region randomization ahead of
 memory_limit

 arch/arm64/mm/init.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 7205a9085b4d..5142020fc146 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -389,6 +389,23 @@ void __init arm64_memblock_init(void)
 		memblock_remove(0, memstart_addr);
 	}
 
+	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
+		extern u16 memstart_offset_seed;
+		u64 range = linear_region_size -
+			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
+
+		/*
+		 * If the size of the linear region exceeds, by a sufficient
+		 * margin, the size of the region that the available physical
+		 * memory spans, randomize the linear region as well.
+		 */
+		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
+			range /= ARM64_MEMSTART_ALIGN;
+			memstart_addr -= ARM64_MEMSTART_ALIGN *
+					 ((range * memstart_offset_seed) >> 16);
+		}
+	}
+
 	/*
 	 * Apply the memory limit if it was set. Since the kernel may be loaded
 	 * high up in memory, add back the kernel region that must be accessible
@@ -428,22 +445,6 @@ void __init arm64_memblock_init(void)
 		}
 	}
 
-	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
-		extern u16 memstart_offset_seed;
-		u64 range = linear_region_size -
-			    (memblock_end_of_DRAM() - memblock_start_of_DRAM());
-
-		/*
-		 * If the size of the linear region exceeds, by a sufficient
-		 * margin, the size of the region that the available physical
-		 * memory spans, randomize the linear region as well.
-		 */
-		if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
-			range /= ARM64_MEMSTART_ALIGN;
-			memstart_addr -= ARM64_MEMSTART_ALIGN *
-					 ((range * memstart_offset_seed) >> 16);
-		}
-	}
 
 	/*
 	 * Register the kernel text, kernel data, initrd, and initial
-- 
2.17.1


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