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authorAndy Lutomirski <luto@amacapital.net>2014-09-23 10:50:54 -0700
committerIngo Molnar <mingo@kernel.org>2014-10-28 11:22:11 +0100
commit9c0080ef93bce34db130db6dc3bd946348e6a203 (patch)
treede4e8e425a37cdc576a83547595febc935410cb9 /arch/x86/vdso
parent258801563ba1be05793f2417ae30557b43a24e4e (diff)
downloadblackbird-op-linux-9c0080ef93bce34db130db6dc3bd946348e6a203.tar.gz
blackbird-op-linux-9c0080ef93bce34db130db6dc3bd946348e6a203.zip
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>
Diffstat (limited to 'arch/x86/vdso')
-rw-r--r--arch/x86/vdso/vma.c2
1 files changed, 1 insertions, 1 deletions
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 */
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