On Tue, Jul 21, 2015 at 1:28 PM, Brian Gerst <brge...@gmail.com> wrote: > 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. >
Really? I thought the whole reason we had three set_thread_area slots was for Wine. --Andy -- 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/
