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Commit 3ac6d8c7 authored by Dan Williams's avatar Dan Williams Committed by Ingo Molnar
Browse files

x86/entry/64: Clear registers for exceptions/interrupts, to reduce speculation attack surface 



Clear the 'extra' registers on entering the 64-bit kernel for exceptions
and interrupts. The common registers are not cleared since they are
likely clobbered well before they can be exploited in a speculative
execution attack.

Originally-From: Andi Kleen <ak@linux.intel.com>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/151787989146.7847.15749181712358213254.stgit@dwillia2-desk3.amr.corp.intel.com


[ Made small improvements to the changelog and the code comments. ]
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 8e1eb3fa

arch/x86/entry/calling.h

+19 −0
Original line number Diff line number Diff line
@@ -147,6 +147,25 @@ For 32-bit we have the following conventions - kernel is built with 
	UNWIND_HINT_REGS offset=\offset

	.endm



	/*

	 * Sanitize registers of values that a speculation attack

	 * might otherwise want to exploit. The lower registers are

	 * likely clobbered well before they could be put to use in

	 * a speculative execution gadget:

	 */

	.macro CLEAR_REGS_NOSPEC

	xorl %ebp, %ebp

	xorl %ebx, %ebx

	xorq %r8, %r8

	xorq %r9, %r9

	xorq %r10, %r10

	xorq %r11, %r11

	xorq %r12, %r12

	xorq %r13, %r13

	xorq %r14, %r14

	xorq %r15, %r15

	.endm



	.macro POP_EXTRA_REGS

	popq %r15

	popq %r14

arch/x86/entry/entry_64.S

+5 −1
Original line number Diff line number Diff line
@@ -575,6 +575,7 @@ END(irq_entries_start) 
	ALLOC_PT_GPREGS_ON_STACK

	SAVE_C_REGS

	SAVE_EXTRA_REGS

	CLEAR_REGS_NOSPEC

	ENCODE_FRAME_POINTER



	testb	$3, CS(%rsp)
@@ -1133,6 +1134,7 @@ ENTRY(xen_failsafe_callback) 
	ALLOC_PT_GPREGS_ON_STACK

	SAVE_C_REGS

	SAVE_EXTRA_REGS

	CLEAR_REGS_NOSPEC

	ENCODE_FRAME_POINTER

	jmp	error_exit

END(xen_failsafe_callback)
@@ -1178,6 +1180,7 @@ ENTRY(paranoid_entry) 
	cld

	SAVE_C_REGS 8

	SAVE_EXTRA_REGS 8

	CLEAR_REGS_NOSPEC

	ENCODE_FRAME_POINTER 8

	movl	$1, %ebx

	movl	$MSR_GS_BASE, %ecx
@@ -1230,8 +1233,8 @@ ENTRY(error_entry) 
	cld

	SAVE_C_REGS 8

	SAVE_EXTRA_REGS 8

	CLEAR_REGS_NOSPEC

	ENCODE_FRAME_POINTER 8

	xorl	%ebx, %ebx

	testb	$3, CS+8(%rsp)

	jz	.Lerror_kernelspace
@@ -1428,6 +1431,7 @@ ENTRY(nmi) 
	pushq	%r14		/* pt_regs->r14 */

	pushq	%r15		/* pt_regs->r15 */

	UNWIND_HINT_REGS

	CLEAR_REGS_NOSPEC

	ENCODE_FRAME_POINTER



	/*