linux-kernel - [PATCH v2 8/9] introduce fetch_random_virt_offset to randomize the kernel text mapping address

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon,  2 Mar 2015 22:58:29 +0800
From:	Baoquan He <bhe@...hat.com>
To:	hpa@...or.com, yinghai@...nel.org, keescook@...omium.org,
	vgoyal@...hat.com, luto@...capital.net, akpm@...ux-foundation.org,
	tglx@...utronix.de, mingo@...hat.com
Cc:	linux-kernel@...r.kernel.org, Baoquan He <bhe@...hat.com>
Subject: [PATCH v2 8/9] introduce fetch_random_virt_offset to randomize the kernel text mapping address

Kaslr extended kernel text mapping region size from 512M to 1G,
namely CONFIG_RANDOMIZE_BASE_MAX_OFFSET. This means kernel text
can be mapped to below region:

[__START_KERNEL_map + LOAD_PHYSICAL_ADDR, __START_KERNEL_map + 1G]

Introduce a function find_random_virt_offset() to get random value
between LOAD_PHYSICAL_ADDR and CONFIG_RANDOMIZE_BASE_MAX_OFFSET.
This random value will be added to __START_KERNEL_map to get the
starting address which kernel text is mapped from. Since slot can
be anywhere of this region, means it is a independent slot_area,
it is easy to get a slot w.r.t random value.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 arch/x86/boot/compressed/aslr.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index 55adee2..332a8c4 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -383,6 +383,28 @@ static unsigned long find_random_phy_addr(unsigned long minimum,
 	return slots_fetch_random();
 }
 
+static unsigned long find_random_virt_offset(unsigned long minimum,
+				  unsigned long image_size)
+{
+	unsigned long slot_num, random;
+	struct mem_vector region, img;
+
+	/* Make sure minimum is aligned. */
+	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
+
+	if ( image_size <= CONFIG_PHYSICAL_ALIGN)
+		slot_num = ( CONFIG_RANDOMIZE_BASE_MAX_OFFSET - minimum ) /
+				CONFIG_PHYSICAL_ALIGN;
+	else
+		slot_num = ( CONFIG_RANDOMIZE_BASE_MAX_OFFSET - minimum - image_size ) /
+				CONFIG_PHYSICAL_ALIGN + 1;
+
+	random = get_random_long() % slot_num;
+
+	return random * CONFIG_PHYSICAL_ALIGN + minimum;
+}
+
+
 static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled)
 {
 	struct setup_data *data;
-- 
1.9.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/