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Commit 3f01daec authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Ingo Molnar
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x86/entry/64: Introduce the PUSH_AND_CLEAN_REGS macro 



Those instances where ALLOC_PT_GPREGS_ON_STACK is called just before
SAVE_AND_CLEAR_REGS can trivially be replaced by PUSH_AND_CLEAN_REGS.
This macro uses PUSH instead of MOV and should therefore be faster, at
least on newer CPUs.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dan.j.williams@intel.com
Link: http://lkml.kernel.org/r/20180211104949.12992-5-linux@dominikbrodowski.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f7bafa2b

arch/x86/entry/calling.h

+36 −0
Original line number Diff line number Diff line
@@ -137,6 +137,42 @@ For 32-bit we have the following conventions - kernel is built with 
	UNWIND_HINT_REGS offset=\offset

	.endm



	.macro PUSH_AND_CLEAR_REGS

	/*

	 * Push registers and 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.

	 * Interleave XOR with PUSH for better uop scheduling:

	 */

	pushq   %rdi		/* pt_regs->di */

	pushq   %rsi		/* pt_regs->si */

	pushq   %rdx		/* pt_regs->dx */

	pushq   %rcx		/* pt_regs->cx */

	pushq   %rax		/* pt_regs->ax */

	pushq   %r8		/* pt_regs->r8 */

	xorq    %r8, %r8	/* nospec   r8 */

	pushq   %r9		/* pt_regs->r9 */

	xorq    %r9, %r9	/* nospec   r9 */

	pushq   %r10		/* pt_regs->r10 */

	xorq    %r10, %r10	/* nospec   r10 */

	pushq   %r11		/* pt_regs->r11 */

	xorq    %r11, %r11	/* nospec   r11*/

	pushq	%rbx		/* pt_regs->rbx */

	xorl    %ebx, %ebx	/* nospec   rbx*/

	pushq	%rbp		/* pt_regs->rbp */

	xorl    %ebp, %ebp	/* nospec   rbp*/

	pushq	%r12		/* pt_regs->r12 */

	xorq    %r12, %r12	/* nospec   r12*/

	pushq	%r13		/* pt_regs->r13 */

	xorq    %r13, %r13	/* nospec   r13*/

	pushq	%r14		/* pt_regs->r14 */

	xorq    %r14, %r14	/* nospec   r14*/

	pushq	%r15		/* pt_regs->r15 */

	xorq    %r15, %r15	/* nospec   r15*/

	UNWIND_HINT_REGS

	.endm



	.macro POP_REGS pop_rdi=1 skip_r11rcx=0

	popq %r15

	popq %r14

arch/x86/entry/entry_64.S

+2 −4
Original line number Diff line number Diff line
@@ -564,8 +564,7 @@ END(irq_entries_start) 
	call	switch_to_thread_stack

1:



	ALLOC_PT_GPREGS_ON_STACK

	SAVE_AND_CLEAR_REGS

	PUSH_AND_CLEAR_REGS

	ENCODE_FRAME_POINTER



	testb	$3, CS(%rsp)
@@ -1112,8 +1111,7 @@ ENTRY(xen_failsafe_callback) 
	addq	$0x30, %rsp

	UNWIND_HINT_IRET_REGS

	pushq	$-1 /* orig_ax = -1 => not a system call */

	ALLOC_PT_GPREGS_ON_STACK

	SAVE_AND_CLEAR_REGS

	PUSH_AND_CLEAR_REGS

	ENCODE_FRAME_POINTER

	jmp	error_exit

END(xen_failsafe_callback)