KAISER: Kernel Address Isolation

This patch introduces our implementation of KAISER (Kernel Address Isolation to
have Side-channels Efficiently Removed), a kernel isolation technique to close
hardware side channels on kernel address information.

More information about the patch can be found on:

        https://github.com/IAIK/KAISER

From: Richard Fellner <richard.fellner@student.tugraz.at>
From: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Subject: [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode
Date: Thu, 4 May 2017 14:26:50 +0200
Link: http://marc.info/?l=linux-kernel&m=149390087310405&w=2
Kaiser-4.10-SHA1: c4b1831d44c6144d3762ccc72f0c4e71a0c713e5

To: <linux-kernel@vger.kernel.org>
To: <kernel-hardening@lists.openwall.com>
Cc: <clementine.maurice@iaik.tugraz.at>
Cc: <moritz.lipp@iaik.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Cc: Richard Fellner <richard.fellner@student.tugraz.at>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <kirill.shutemov@linux.intel.com>
Cc: <anders.fogh@gdata-adan.de>

After several recent works [1,2,3] KASLR on x86_64 was basically
considered dead by many researchers. We have been working on an
efficient but effective fix for this problem and found that not mapping
the kernel space when running in user mode is the solution to this
problem [4] (the corresponding paper [5] will be presented at ESSoS17).

With this RFC patch we allow anybody to configure their kernel with the
flag CONFIG_KAISER to add our defense mechanism.

If there are any questions we would love to answer them.
We also appreciate any comments!

Cheers,
Daniel (+ the KAISER team from Graz University of Technology)

[1] http://www.ieee-security.org/TC/SP2013/papers/4977a191.pdf
[2] https://www.blackhat.com/docs/us-16/materials/us-16-Fogh-Using-Undocumented-CPU-Behaviour-To-See-Into-Kernel-Mode-And-Break-KASLR-In-The-Process.pdf
[3] https://www.blackhat.com/docs/us-16/materials/us-16-Jang-Breaking-Kernel-Address-Space-Layout-Randomization-KASLR-With-Intel-TSX.pdf
[4] https://github.com/IAIK/KAISER
[5] https://gruss.cc/files/kaiser.pdf

[patch based also on
https://raw.githubusercontent.com/IAIK/KAISER/master/KAISER/0001-KAISER-Kernel-Address-Isolation.patch]

Signed-off-by: Richard Fellner <richard.fellner@student.tugraz.at>
Signed-off-by: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
Signed-off-by: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Signed-off-by: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 23 insertions, 1 deletions

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index e7b0e7ff4c58..9467a2c4bc60 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -36,6 +36,7 @@
 #include <asm/smap.h>
 #include <asm/pgtable_types.h>
 #include <asm/export.h>
+#include <asm/kaiser.h>
 #include <linux/err.h>
 
 /* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
@@ -146,6 +147,7 @@ ENTRY(entry_SYSCALL_64)
 	 * it is too small to ever cause noticeable irq latency.
 	 */
 	SWAPGS_UNSAFE_STACK
+	SWITCH_KERNEL_CR3_NO_STACK
 	/*
 	 * A hypervisor implementation might want to use a label
 	 * after the swapgs, so that it can do the swapgs
@@ -228,6 +230,7 @@ entry_SYSCALL_64_fastpath:
 	movq	RIP(%rsp), %rcx
 	movq	EFLAGS(%rsp), %r11
 	RESTORE_C_REGS_EXCEPT_RCX_R11
+	SWITCH_USER_CR3
 	movq	RSP(%rsp), %rsp
 	USERGS_SYSRET64
 
@@ -323,10 +326,12 @@ return_from_SYSCALL_64:
 syscall_return_via_sysret:
 	/* rcx and r11 are already restored (see code above) */
 	RESTORE_C_REGS_EXCEPT_RCX_R11
+	SWITCH_USER_CR3
 	movq	RSP(%rsp), %rsp
 	USERGS_SYSRET64
 
 opportunistic_sysret_failed:
+	SWITCH_USER_CR3
 	SWAPGS
 	jmp	restore_c_regs_and_iret
 END(entry_SYSCALL_64)
@@ -424,6 +429,7 @@ ENTRY(ret_from_fork)
 	movq	%rsp, %rdi
 	call	syscall_return_slowpath	/* returns with IRQs disabled */
 	TRACE_IRQS_ON			/* user mode is traced as IRQS on */
+	SWITCH_USER_CR3
 	SWAPGS
 	jmp	restore_regs_and_iret
 
@@ -478,6 +484,7 @@ END(irq_entries_start)
 	 * tracking that we're in kernel mode.
 	 */
 	SWAPGS
+	SWITCH_KERNEL_CR3
 
 	/*
 	 * We need to tell lockdep that IRQs are off.  We can't do this until
@@ -535,6 +542,7 @@ GLOBAL(retint_user)
 	mov	%rsp,%rdi
 	call	prepare_exit_to_usermode
 	TRACE_IRQS_IRETQ
+	SWITCH_USER_CR3
 	SWAPGS
 	jmp	restore_regs_and_iret
 
@@ -612,6 +620,7 @@ native_irq_return_ldt:
 
 	pushq	%rdi				/* Stash user RDI */
 	SWAPGS
+	SWITCH_KERNEL_CR3
 	movq	PER_CPU_VAR(espfix_waddr), %rdi
 	movq	%rax, (0*8)(%rdi)		/* user RAX */
 	movq	(1*8)(%rsp), %rax		/* user RIP */
@@ -638,6 +647,7 @@ native_irq_return_ldt:
 	 * still points to an RO alias of the ESPFIX stack.
 	 */
 	orq	PER_CPU_VAR(espfix_stack), %rax
+	SWITCH_USER_CR3
 	SWAPGS
 	movq	%rax, %rsp
 
@@ -1034,6 +1044,7 @@ ENTRY(paranoid_entry)
 	testl	%edx, %edx
 	js	1f				/* negative -> in kernel */
 	SWAPGS
+	SWITCH_KERNEL_CR3
 	xorl	%ebx, %ebx
 1:	ret
 END(paranoid_entry)
@@ -1056,6 +1067,7 @@ ENTRY(paranoid_exit)
 	testl	%ebx, %ebx			/* swapgs needed? */
 	jnz	paranoid_exit_no_swapgs
 	TRACE_IRQS_IRETQ
+	SWITCH_USER_CR3_NO_STACK
 	SWAPGS_UNSAFE_STACK
 	jmp	paranoid_exit_restore
 paranoid_exit_no_swapgs:
@@ -1084,6 +1096,7 @@ ENTRY(error_entry)
 	 * from user mode due to an IRET fault.
 	 */
 	SWAPGS
+	SWITCH_KERNEL_CR3
 
 .Lerror_entry_from_usermode_after_swapgs:
 	/*
@@ -1135,6 +1148,7 @@ ENTRY(error_entry)
 	 * Switch to kernel gsbase:
 	 */
 	SWAPGS
+	SWITCH_KERNEL_CR3
 
 	/*
 	 * Pretend that the exception came from user mode: set up pt_regs
@@ -1235,6 +1249,7 @@ ENTRY(nmi)
 	 */
 
 	SWAPGS_UNSAFE_STACK
+	SWITCH_KERNEL_CR3_NO_STACK
 	cld
 	movq	%rsp, %rdx
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
@@ -1275,6 +1290,7 @@ ENTRY(nmi)
 	 * work, because we don't want to enable interrupts.  Fortunately,
 	 * do_nmi doesn't modify pt_regs.
 	 */
+	SWITCH_USER_CR3
 	SWAPGS
 	jmp	restore_c_regs_and_iret
 
@@ -1486,6 +1502,7 @@ end_repeat_nmi:
 	testl	%ebx, %ebx			/* swapgs needed? */
 	jnz	nmi_restore
 nmi_swapgs:
+	SWITCH_USER_CR3_NO_STACK
 	SWAPGS_UNSAFE_STACK
 nmi_restore:
 	RESTORE_EXTRA_REGS
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index e1721dafbcb1..f0e384ee8fc6 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -13,6 +13,7 @@
 #include <asm/irqflags.h>
 #include <asm/asm.h>
 #include <asm/smap.h>
+#include <asm/kaiser.h>
 #include <linux/linkage.h>
 #include <linux/err.h>
 
@@ -48,6 +49,7 @@
 ENTRY(entry_SYSENTER_compat)
 	/* Interrupts are off on entry. */
 	SWAPGS_UNSAFE_STACK
+	SWITCH_KERNEL_CR3_NO_STACK
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
 	/*
@@ -184,6 +186,7 @@ ENDPROC(entry_SYSENTER_compat)
 ENTRY(entry_SYSCALL_compat)
 	/* Interrupts are off on entry. */
 	SWAPGS_UNSAFE_STACK
+	SWITCH_KERNEL_CR3_NO_STACK
 
 	/* Stash user ESP and switch to the kernel stack. */
 	movl	%esp, %r8d
@@ -259,6 +262,7 @@ sysret32_from_system_call:
 	xorq	%r8, %r8
 	xorq	%r9, %r9
 	xorq	%r10, %r10
+	SWITCH_USER_CR3
 	movq	RSP-ORIG_RAX(%rsp), %rsp
 	swapgs
 	sysretl
@@ -297,7 +301,7 @@ ENTRY(entry_INT80_compat)
 	PARAVIRT_ADJUST_EXCEPTION_FRAME
 	ASM_CLAC			/* Do this early to minimize exposure */
 	SWAPGS
-
+	SWITCH_KERNEL_CR3_NO_STACK
 	/*
 	 * User tracing code (ptrace or signal handlers) might assume that
 	 * the saved RAX contains a 32-bit number when we're invoking a 32-bit
@@ -338,6 +342,7 @@ ENTRY(entry_INT80_compat)
 
 	/* Go back to user mode. */
 	TRACE_IRQS_ON
+	SWITCH_USER_CR3_NO_STACK
 	SWAPGS
 	jmp	restore_regs_and_iret
 END(entry_INT80_compat)