linux-kernel - [PATCH v3 13/19] x86, kaslr: Introduce struct slot

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Date:	Sat,  5 Mar 2016 00:25:11 +0800
From:	Baoquan He <bhe@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	yinghai@...nel.org, keescook@...omium.org, hpa@...or.com,
	vgoyal@...hat.com, mingo@...hat.com, bp@...en8.de, luto@...nel.org,
	lasse.collin@...aani.org, akpm@...ux-foundation.org,
	dyoung@...hat.com, Baoquan He <bhe@...hat.com>
Subject: [PATCH v3 13/19] x86, kaslr: Introduce struct slot_area to manage randomization slot info

Kernel is expected to be randomly reloaded anywhere in the whole
physical memory area, it could be near 64T at most. In this case
there could be about 4*1024*1024 randomization slots if
CONFIG_PHYSICAL_ALIGN is 0x1000000. Currently the starting address
of candidate position is stored into array slots[], and it finds
each available slot one time and save it into slots[]. With this
old way the slot arrry will cost too much memory and it's also
very unefficient to get and save the slot information into slot
array one by one.

Here introduce struct slot_area to manage randomization slot info
in one contiguous memory area excluding the avoid area. Each
slot_area will contain the starting address and how many available
slots in this area. Array slot_areas is used to store all slot area
info.

Since setup_data is a linked list, could contain many datas by
pointer to point one by one, excluding them will split RAM memory
into many smaller areas, here only take the first 100 slot areas if
too many of them.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 arch/x86/boot/compressed/aslr.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index 35f2eac..7fc22a6 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -216,8 +216,20 @@ static bool mem_avoid_overlap(struct mem_vector *img)

 static unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
 			   CONFIG_PHYSICAL_ALIGN];
+
+struct slot_area {
+	unsigned long addr;
+	int num;
+};
+
+#define MAX_SLOT_AREA 100
+
+static struct slot_area slot_areas[MAX_SLOT_AREA];
+
 static unsigned long slot_max;

+static unsigned long slot_area_index;
+
 static void slots_append(unsigned long addr)
 {
 	/* Overflowing the slots list should be impossible. */
-- 
2.5.0