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Subject[PATCH 5/8] x86,vdso: Make the PER_CPU segment 32 bits
Date
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>
---
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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