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x86/vdso: Make the PER_CPU segment 32 bits

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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>
This commit is contained in:
Andy Lutomirski 2014-09-23 10:50:55 -07:00 committed by Ingo Molnar
parent 9c0080ef93
commit 287e013108
1 changed files with 1 additions and 0 deletions
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arch/x86/vdso/vma.c
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@ -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);