linux-kernel - [PATCH 5/8] x86,vdso: Make the PER

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Date:	Tue, 23 Sep 2014 10:50:55 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 5/8] x86,vdso: Make the PER_CPU segment 32 bits

IMO users ought not to be able to use 16-bit segments without using
modify_ldt.  Fortunately, it's impossible to break espfix64 by
loading the PER_CPU segment into SS because it's PER_CPU is marked
read-only and SS cannot contain an RO segment, but marking PER_CPU
as 32-bit is less fragile.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
 arch/x86/vdso/vma.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 0c7997467be0..32ca60c8157b 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -268,6 +268,7 @@ static void vsyscall_set_cpu(int cpu)
 		.dpl = 3,		/* Visible to user code */
 		.s = 1,			/* Not a system segment */
 		.p = 1,			/* Present */
+		.d = 1,			/* 32-bit */
 	};
 
 	write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
-- 
1.9.3

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