On Tue, Jul 21, 2015 at 3:59 PM, Andy Lutomirski <l...@kernel.org> wrote: > The modify_ldt syscall exposes a large attack surface and is > unnecessary for modern userspace. Make it optional. > > Signed-off-by: Andy Lutomirski <l...@kernel.org> > --- > arch/x86/Kconfig | 17 +++++++++++++++++ > arch/x86/include/asm/mmu.h | 2 ++ > arch/x86/include/asm/mmu_context.h | 31 +++++++++++++++++++++++-------- > arch/x86/kernel/Makefile | 3 ++- > arch/x86/kernel/cpu/perf_event.c | 4 ++++ > arch/x86/kernel/process_64.c | 2 ++ > arch/x86/kernel/step.c | 2 ++ > kernel/sys_ni.c | 1 + > 8 files changed, 53 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 55bced17dc95..a7ff3980bd65 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -1009,6 +1009,7 @@ config VM86 > config X86_16BIT > bool "Enable support for 16-bit segments" if EXPERT > default y > + depends on MODIFY_LDT_SYSCALL > ---help--- > This option is required by programs like Wine to run 16-bit > protected mode legacy code on x86 processors. Disabling > @@ -2047,6 +2048,22 @@ config CMDLINE_OVERRIDE > This is used to work around broken boot loaders. This should > be set to 'N' under normal conditions. > > +config MODIFY_LDT_SYSCALL > + bool "Enable the LDT (local descriptor table)" if EXPERT > + default y > + ---help--- > + Linux can allow user programs to install a per-process x86 > + Local Descriptor Table (LDT) using the modify_ldt(2) system > + call. This is required to run 16-bit or segmented code such as > + DOSEMU or some Wine programs. It is also used by some very old > + threading libraries. > + > + Enabling this feature adds a small amount of overhead to > + context switches and increases the low-level kernel attack > + surface. Disabling it removes the modify_ldt(2) system call. > + > + Saying 'N' here may make sense for embedded or server kernels. > +
I believe Wine still uses the LDT for thread-local data, even for 32 and 64-bit programs. This is separate from the Linux runtime TLS. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
