Messages in this thread Patch in this message | | | From | Andy Lutomirski <> | Subject | [PATCH 4/8] x86,vdso: Make the PER_CPU segment start out accessed | Date | Tue, 23 Sep 2014 10:50:54 -0700 |
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The first userspace attempt to read or write the PER_CPU segment will write the accessed bit to the GDT. This is visible to userspace using the LAR instruction, and it also pointlessly dirties a cache line.
Set the segment's accessed bit at boot to prevent userspace access to segments from having side effects.
Signed-off-by: Andy Lutomirski <luto@amacapital.net> --- arch/x86/vdso/vma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c index 261b1349acc9..0c7997467be0 100644 --- a/arch/x86/vdso/vma.c +++ b/arch/x86/vdso/vma.c @@ -264,7 +264,7 @@ static void vsyscall_set_cpu(int cpu) d = (struct desc_struct) { .limit0 = cpu | ((node & 0xf) << 12), .limit = node >> 4, - .type = 4, /* RO data, expand down */ + .type = 5, /* RO data, expand down, accessed */ .dpl = 3, /* Visible to user code */ .s = 1, /* Not a system segment */ .p = 1, /* Present */ -- 1.9.3
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