linux-kernel - [PATCH 2/3] x86/entry: Clear registers for 64bit exceptions/interrupts

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Date:   Sat, 03 Feb 2018 15:21:42 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     tglx@...utronix.de
Cc:     Andi Kleen <ak@...ux.intel.com>, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, luto@...nel.org
Subject: [PATCH 2/3] x86/entry: Clear registers for 64bit
 exceptions/interrupts

From: Andi Kleen <ak@...ux.intel.com>

Clear the 'extra' registers on entering the 64bit 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.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 arch/x86/entry/entry_64.S |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 46260e951da6..d73eedf1eb47 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -563,6 +563,7 @@ END(irq_entries_start)
 	ALLOC_PT_GPREGS_ON_STACK
 	SAVE_C_REGS
 	SAVE_EXTRA_REGS
+	CLEAR_EXTRA_REGS_NOSPEC
 	ENCODE_FRAME_POINTER
 
 	testb	$3, CS(%rsp)
@@ -1121,6 +1122,7 @@ ENTRY(xen_failsafe_callback)
 	ALLOC_PT_GPREGS_ON_STACK
 	SAVE_C_REGS
 	SAVE_EXTRA_REGS
+	CLEAR_EXTRA_REGS_NOSPEC
 	ENCODE_FRAME_POINTER
 	jmp	error_exit
 END(xen_failsafe_callback)
@@ -1166,6 +1168,7 @@ ENTRY(paranoid_entry)
 	cld
 	SAVE_C_REGS 8
 	SAVE_EXTRA_REGS 8
+	CLEAR_EXTRA_REGS_NOSPEC
 	ENCODE_FRAME_POINTER 8
 	movl	$1, %ebx
 	movl	$MSR_GS_BASE, %ecx
@@ -1218,6 +1221,7 @@ ENTRY(error_entry)
 	cld
 	SAVE_C_REGS 8
 	SAVE_EXTRA_REGS 8
+	CLEAR_EXTRA_REGS_NOSPEC
 	ENCODE_FRAME_POINTER 8
 	xorl	%ebx, %ebx
 	testb	$3, CS+8(%rsp)
@@ -1416,6 +1420,7 @@ ENTRY(nmi)
 	pushq	%r14		/* pt_regs->r14 */
 	pushq	%r15		/* pt_regs->r15 */
 	UNWIND_HINT_REGS
+	CLEAR_EXTRA_REGS_NOSPEC
 	ENCODE_FRAME_POINTER
 
 	/*