linux-kernel - [PATCH v1 4/8] x86/entry/retpoline: Clear extra registers for compat syscalls

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Date:   Tue,  9 Jan 2018 17:03:24 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     tglx@...utronix.de
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, dwmw@...zon.co.uk, pjt@...gle.com,
        luto@...nel.org, peterz@...radead.org, thomas.lendacky@....com,
        tim.c.chen@...ux.intel.com, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, jikos@...nel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH v1 4/8] x86/entry/retpoline: Clear extra registers for compat syscalls

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

Clear all registers for compat calls on 64bit kernels. All arguments
are initially passed through the stack, so this is fairly simple
without additional stubs.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/entry/entry_64_compat.S | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 98d5358e4041..16fd2643a77f 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -95,6 +95,8 @@ ENTRY(entry_SYSENTER_compat)
 	pushq   $0			/* pt_regs->r14 = 0 */
 	pushq   $0			/* pt_regs->r15 = 0 */
 	cld
+	/* Can clear all because arguments are passed through the stack */
+	CLEAR_ALL_REGS
 
 	/*
 	 * SYSENTER doesn't filter flags, so we need to clear NT and AC
@@ -223,6 +225,8 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
 	pushq   $0			/* pt_regs->r13 = 0 */
 	pushq   $0			/* pt_regs->r14 = 0 */
 	pushq   $0			/* pt_regs->r15 = 0 */
+	/* Can clear all because arguments are passed through the stack */
+	CLEAR_ALL_REGS
 
 	/*
 	 * User mode is traced as though IRQs are on, and SYSENTER
@@ -348,6 +352,8 @@ ENTRY(entry_INT80_compat)
 	pushq   %r14                    /* pt_regs->r14 */
 	pushq   %r15                    /* pt_regs->r15 */
 	cld
+	/* Can clear all because arguments are passed through the stack */
+	CLEAR_ALL_REGS
 
 	/*
 	 * User mode is traced as though IRQs are on, and the interrupt
-- 
2.14.3