x86_64 specialized way of defining the base address for the alternate
mapping used by write-rare.
Since the kernel address space spans across 64TB and it is mapped into a
used address space of 128TB, the kernel address space can be shifted by a
random offset that is up to 64TB and page aligned.
This is accomplished by providing arch-specific version of the function
__init_wr_base()
Signed-off-by: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Nadav Amit <nadav.amit@xxxxxxxxx>
CC: Matthew Wilcox <willy@xxxxxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CC: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
CC: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
CC: Ahmed Soliman <ahmedsoliman@xxxxxxxxxxx>
CC: linux-integrity@xxxxxxxxxxxxxxx
CC: kernel-hardening@xxxxxxxxxxxxxxxxxx
CC: linux-mm@xxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
arch/x86/mm/Makefile | 2 ++
arch/x86/mm/prmem.c (new) | 20 ++++++++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 4b101dd6e52f..66652de1e2c7 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -53,3 +53,5 @@ obj-$(CONFIG_PAGE_TABLE_ISOLATION) += pti.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_identity.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_boot.o
+
+obj-$(CONFIG_PRMEM) += prmem.o
diff --git a/arch/x86/mm/prmem.c b/arch/x86/mm/prmem.c
new file mode 100644
index 000000000000..b04fc03f92fb
--- /dev/null
+++ b/arch/x86/mm/prmem.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * prmem.c: Memory Protection Library - x86_64 backend
+ *
+ * (C) Copyright 2018-2019 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <igor.stoppa@xxxxxxxxxx>
+ */
+
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
+
+unsigned long __init __init_wr_base(void)
+{
+ /*
+ * Place 64TB of kernel address space within 128TB of user address
+ * space, at a random page aligned offset.
+ */
+ return (((unsigned long)kaslr_get_random_long("WR Poke")) &
+ PAGE_MASK) % (64 * _BITUL(40));
+}
--
2.19.1
