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 <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
