linux-kernel - [PATCH 3/3] x86,vdso: Make the PER

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Date:	Fri, 25 Jul 2014 18:13:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 3/3] 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 a read-only
segment, but marking it 32-bit seems less fragile.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
 arch/x86/kernel/vsyscall_64.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 0e2c229..87ab841 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -309,6 +309,7 @@ static void vsyscall_set_cpu(int cpu)
 	d.dpl = 3;		/* Visible to user code */
 	d.s = 1;		/* Non a system segment */
 	d.p = 1;		/* Present */
+	d.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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