linux-kernel - [PATCH 06/11] x86-64: Fix %cs value in convert_from

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Message-Id: <1283011478-27237-7-git-send-email-brgerst@gmail.com>
Date:	Sat, 28 Aug 2010 12:04:33 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	hpa@...or.com
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 06/11] x86-64: Fix %cs value in convert_from_fxsr()

While %ds still contains the userspace selector, %cs is KERNEL_CS
at this point.  Always get %cs from pt_regs.

It actually is possible to get the correct segments for compat tasks,
but that involves using the [f]xsave instruction without a REX.W prefix.

Signed-off-by: Brian Gerst <brgerst@...il.com>
---
 arch/x86/kernel/i387.c |   18 ++++++++----------
 1 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index c795675..b1a732d 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -383,19 +383,17 @@ convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
 #ifdef CONFIG_X86_64
 	env->fip = fxsave->rip;
 	env->foo = fxsave->rdp;
+	/*
+	 * should be actually ds/cs at fpu exception time, but
+	 * that information is not available in 64bit mode.
+	 */
+	env->fcs = task_pt_regs(tsk)->cs;
 	if (tsk == current) {
-		/*
-		 * should be actually ds/cs at fpu exception time, but
-		 * that information is not available in 64bit mode.
-		 */
-		asm("mov %%ds, %[fos]" : [fos] "=r" (env->fos));
-		asm("mov %%cs, %[fcs]" : [fcs] "=r" (env->fcs));
+		savesegment(ds, env->fos);
 	} else {
-		struct pt_regs *regs = task_pt_regs(tsk);
-
-		env->fos = 0xffff0000 | tsk->thread.ds;
-		env->fcs = regs->cs;
+		env->fos = tsk->thread.ds;
 	}
+	env->fos |= 0xffff0000;
 #else
 	env->fip = fxsave->fip;
 	env->fcs = (u16) fxsave->fcs | ((u32) fxsave->fop << 16);
-- 
1.7.2.2

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