linux-kernel - [PATCH v3 2/7] x86/ldt: use a common value for read_default

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Date:   Thu, 21 Jun 2018 14:17:49 -0700
From:   "H. Peter Anvin, Intel" <h.peter.anvin@...el.com>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     "H. Peter Anvin" <hpa@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        "Chang S . Bae" <chang.seok.bae@...el.com>,
        "Markus T . Metzger" <markus.t.metzger@...el.com>
Subject: [PATCH v3 2/7] x86/ldt: use a common value for read_default_ldt()

From: "H. Peter Anvin" <hpa@...ux.intel.com>

There is no point in having two different sizes for the "default ldt";
a concept which is obsolete anyway.  Since this is kernel-dependent
and not user-space dependent, a 32-bit app needs to be able to accept
the 64-bit value anyway, so use that value, which is the larger of the
two.

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Chang S. Bae <chang.seok.bae@...el.com>
Cc: Markus T. Metzger <markus.t.metzger@...el.com>
---
 arch/x86/kernel/ldt.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index 18e9f4c0633d..601d24268a99 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -383,12 +383,8 @@ static int read_ldt(void __user *ptr, unsigned long bytecount)
 
 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
 {
-	/* CHECKME: Can we use _one_ random number ? */
-#ifdef CONFIG_X86_32
-	unsigned long size = 5 * sizeof(struct desc_struct);
-#else
-	unsigned long size = 128;
-#endif
+	const unsigned long size = 128;
+
 	if (bytecount > size)
 		bytecount = size;
 	if (clear_user(ptr, bytecount))
-- 
2.14.4