Messages in this thread Patch in this message | | | Date | Tue, 28 Oct 2014 04:15:22 -0700 | From | tip-bot for Andy Lutomirski <> | Subject | [tip:x86/vdso] x86/vdso: Make the PER_CPU segment start out accessed |
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Commit-ID: 9c0080ef93bce34db130db6dc3bd946348e6a203 Gitweb: http://git.kernel.org/tip/9c0080ef93bce34db130db6dc3bd946348e6a203 Author: Andy Lutomirski <luto@amacapital.net> AuthorDate: Tue, 23 Sep 2014 10:50:54 -0700 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 28 Oct 2014 11:22:11 +0100
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> --- 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 261b134..0c799746 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 */
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