[PATCH 3/3] x86,vdso: Make the PER_CPU segment 32 bits

Andy Lutomirski
2014-07-26T01:13:27Z

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@amacapital.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