linux-kernel - [PATCH] x86/ldt: correct ldt access in single stepping logic

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Date:	Thu,  6 Aug 2015 10:04:38 +0200
From:	Juergen Gross <jgross@...e.com>
To:	luto@...nel.org, bp@...e.de, x86@...nel.org, hpa@...or.com,
	mingo@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org
Cc:	Juergen Gross <jgross@...e.com>, <stable@...r.kernel.org>
Subject: [PATCH] x86/ldt: correct ldt access in single stepping logic

Commit 37868fe113ff ("x86/ldt: Make modify_ldt synchronous") introduced
a new struct ldt_struct anchored at mm->context.ldt.

convert_ip_to_linear() was changed to reflect this, but indexing into
the ldt has to be changed as the pointer is no longer void *.

Cc: <stable@...r.kernel.org> # 37868fe113ff: x86/ldt: Make modify_ldt synchronous
Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/kernel/step.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 6273324..0ccb53a 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -28,11 +28,11 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re
 		struct desc_struct *desc;
 		unsigned long base;
 
-		seg &= ~7UL;
+		seg >>= 3;
 
 		mutex_lock(&child->mm->context.lock);
 		if (unlikely(!child->mm->context.ldt ||
-			     (seg >> 3) >= child->mm->context.ldt->size))
+			     seg >= child->mm->context.ldt->size))
 			addr = -1L; /* bogus selector, access would fault */
 		else {
 			desc = &child->mm->context.ldt->entries[seg];
-- 
2.1.4

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