linux-kernel - [RFC 01/10] x86/mm/kaslr: refactor to use enum indices for regions

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Date:   Wed, 12 Jun 2019 19:08:26 +0200
From:   Marius Hillenbrand <mhillenb@...zon.de>
To:     kvm@...r.kernel.org
Cc:     Marius Hillenbrand <mhillenb@...zon.de>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        linux-mm@...ck.org, Alexander Graf <graf@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: [RFC 01/10] x86/mm/kaslr: refactor to use enum indices for regions

The KASLR randomization code currently refers to specific regions, such
as the vmalloc area, by literal indices into an array. When adding new
regions, we have to be careful to also change all indices that may
potentially change. Avoid that risk by introducing an enum used as
indices.

Signed-off-by: Marius Hillenbrand <mhillenb@...zon.de>
Cc: Alexander Graf <graf@...zon.de>
Cc: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/mm/kaslr.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 3f452ffed7e9..c455f1ffba29 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -41,6 +41,12 @@
  */
 static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE;
 
+enum {
+	PHYSMAP,
+	VMALLOC,
+	VMMEMMAP,
+};
+
 /*
  * Memory regions randomized by KASLR (except modules that use a separate logic
  * earlier during boot). The list is ordered based on virtual addresses. This
@@ -50,9 +56,9 @@ static __initdata struct kaslr_memory_region {
 	unsigned long *base;
 	unsigned long size_tb;
 } kaslr_regions[] = {
-	{ &page_offset_base, 0 },
-	{ &vmalloc_base, 0 },
-	{ &vmemmap_base, 1 },
+	[PHYSMAP] = { &page_offset_base, 0 },
+	[VMALLOC] = { &vmalloc_base, 0 },
+	[VMMEMMAP] = { &vmemmap_base, 1 },
 };
 
 /* Get size in bytes used by the memory region */
@@ -94,20 +100,20 @@ void __init kernel_randomize_memory(void)
 	if (!kaslr_memory_enabled())
 		return;
 
-	kaslr_regions[0].size_tb = 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT);
-	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;
+	kaslr_regions[PHYSMAP].size_tb = 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT);
+	kaslr_regions[VMALLOC].size_tb = VMALLOC_SIZE_TB;
 
 	/*
 	 * Update Physical memory mapping to available and
 	 * add padding if needed (especially for memory hotplug support).
 	 */
-	BUG_ON(kaslr_regions[0].base != &page_offset_base);
+	BUG_ON(kaslr_regions[PHYSMAP].base != &page_offset_base);
 	memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
 		CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
 
 	/* Adapt phyiscal memory region size based on available memory */
-	if (memory_tb < kaslr_regions[0].size_tb)
-		kaslr_regions[0].size_tb = memory_tb;
+	if (memory_tb < kaslr_regions[PHYSMAP].size_tb)
+		kaslr_regions[PHYSMAP].size_tb = memory_tb;
 
 	/* Calculate entropy available between regions */
 	remain_entropy = vaddr_end - vaddr_start;
-- 
2.21.0