Commit 9c0080ef authored Sep 23, 2014 by Andy Lutomirski Committed by Ingo Molnar Oct 28, 2014

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 <luto@amacapital.net>
Link: http://lkml.kernel.org/r/ac63814ca4c637a08ec2fd0360d67ca67560a9ee.1411494540.git.luto@amacapital.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 25880156

arch/x86/vdso/vma.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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 */

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