From 9c0080ef93bce34db130db6dc3bd946348e6a203 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Tue, 23 Sep 2014 10:50:54 -0700 Subject: x86/vdso: Make the PER_CPU segment start out accessed 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 Link: http://lkml.kernel.org/r/ac63814ca4c637a08ec2fd0360d67ca67560a9ee.1411494540.git.luto@amacapital.net Signed-off-by: Ingo Molnar --- arch/x86/vdso/vma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/vdso') 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 */ -- cgit v1.2.3