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@amacapital.net>
Link: http://lkml.kernel.org/r/179f490d659307873eefd09206bebd417e2ab5ad.1411494540.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 0c799746..32ca60c 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -268,6 +268,7 @@
.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);