From: Andy Lutomirski Date: Tue, 23 Sep 2014 17:50:54 +0000 (-0700) Subject: x86/vdso: Make the PER_CPU segment start out accessed X-Git-Tag: omap-for-v3.19/fixes-rc1~152^2~10 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=9c0080ef93bce34db130db6dc3bd946348e6a203 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 --- 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 */