diff options
| -rw-r--r-- | arch/x86/Kconfig | 18 | ||||
| -rw-r--r-- | arch/x86/include/asm/mmu.h | 2 | ||||
| -rw-r--r-- | arch/x86/include/asm/mmu_context.h | 28 | ||||
| -rw-r--r-- | arch/x86/kernel/Makefile | 3 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/perf_event.c | 4 | ||||
| -rw-r--r-- | arch/x86/kernel/process_64.c | 2 | ||||
| -rw-r--r-- | arch/x86/kernel/step.c | 2 | ||||
| -rw-r--r-- | kernel/sys_ni.c | 1 |
8 files changed, 52 insertions, 8 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index e26fe7a5b9e6..798658048db3 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1036,6 +1036,7 @@ 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 @@ -1530,6 +1531,7 @@ config X86_RESERVE_LOW config MATH_EMULATION bool + depends on MODIFY_LDT_SYSCALL prompt "Math emulation" if X86_32 ---help--- Linux can emulate a math coprocessor (used for floating point @@ -2074,6 +2076,22 @@ 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. + source "kernel/livepatch/Kconfig" endmenu diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h index 364d27481a52..55234d5e7160 100644 --- a/arch/x86/include/asm/mmu.h +++ b/arch/x86/include/asm/mmu.h @@ -9,7 +9,9 @@ * we put the segment information here. */ typedef struct { +#ifdef CONFIG_MODIFY_LDT_SYSCALL struct ldt_struct *ldt; +#endif #ifdef CONFIG_X86_64 /* True if mm supports a task running in 32 bit compatibility mode. */ diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 984abfe47edc..379cd3658799 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -33,6 +33,7 @@ static inline void load_mm_cr4(struct mm_struct *mm) static inline void load_mm_cr4(struct mm_struct *mm) {} #endif +#ifdef CONFIG_MODIFY_LDT_SYSCALL /* * ldt_structs can be allocated, used, and freed, but they are never * modified while live. @@ -48,8 +49,23 @@ struct ldt_struct { int size; }; +/* + * Used for LDT copy/destruction. + */ +int init_new_context(struct task_struct *tsk, struct mm_struct *mm); +void destroy_context(struct mm_struct *mm); +#else /* CONFIG_MODIFY_LDT_SYSCALL */ +static inline int init_new_context(struct task_struct *tsk, + struct mm_struct *mm) +{ + return 0; +} +static inline void destroy_context(struct mm_struct *mm) {} +#endif + static inline void load_mm_ldt(struct mm_struct *mm) { +#ifdef CONFIG_MODIFY_LDT_SYSCALL struct ldt_struct *ldt; /* lockless_dereference synchronizes with smp_store_release */ @@ -73,17 +89,13 @@ static inline void load_mm_ldt(struct mm_struct *mm) set_ldt(ldt->entries, ldt->size); else clear_LDT(); +#else + clear_LDT(); +#endif DEBUG_LOCKS_WARN_ON(preemptible()); } -/* - * Used for LDT copy/destruction. - */ -int init_new_context(struct task_struct *tsk, struct mm_struct *mm); -void destroy_context(struct mm_struct *mm); - - static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) { #ifdef CONFIG_SMP @@ -114,6 +126,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, /* Load per-mm CR4 state */ load_mm_cr4(next); +#ifdef CONFIG_MODIFY_LDT_SYSCALL /* * Load the LDT, if the LDT is different. * @@ -128,6 +141,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, */ if (unlikely(prev->context.ldt != next->context.ldt)) load_mm_ldt(next); +#endif } #ifdef CONFIG_SMP else { diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index dc19730ad0db..514064897d55 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -25,7 +25,8 @@ CFLAGS_irq.o := -I$(src)/../include/asm/trace obj-y := process_$(BITS).o signal.o obj-$(CONFIG_COMPAT) += signal_compat.o obj-y += traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o -obj-y += time.o ioport.o ldt.o dumpstack.o nmi.o +obj-y += time.o ioport.o dumpstack.o nmi.o +obj-$(CONFIG_MODIFY_LDT_SYSCALL) += ldt.o obj-y += setup.o x86_init.o i8259.o irqinit.o jump_label.o obj-$(CONFIG_IRQ_WORK) += irq_work.o obj-y += probe_roms.o diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index 09f9ff271df4..cc25c8f3512d 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -2179,6 +2179,7 @@ static unsigned long get_segment_base(unsigned int segment) int idx = segment >> 3; if ((segment & SEGMENT_TI_MASK) == SEGMENT_LDT) { +#ifdef CONFIG_MODIFY_LDT_SYSCALL struct ldt_struct *ldt; if (idx > LDT_ENTRIES) @@ -2190,6 +2191,9 @@ static unsigned long get_segment_base(unsigned int segment) return 0; desc = &ldt->entries[idx]; +#else + return 0; +#endif } else { if (idx > GDT_ENTRIES) return 0; diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 7ff035c6c54d..3c1bbcf12924 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -121,6 +121,7 @@ void __show_regs(struct pt_regs *regs, int all) void release_thread(struct task_struct *dead_task) { if (dead_task->mm) { +#ifdef CONFIG_MODIFY_LDT_SYSCALL if (dead_task->mm->context.ldt) { pr_warn("WARNING: dead process %s still has LDT? <%p/%d>\n", dead_task->comm, @@ -128,6 +129,7 @@ void release_thread(struct task_struct *dead_task) dead_task->mm->context.ldt->size); BUG(); } +#endif } } diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index 6273324186ac..fd88e152d584 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -18,6 +18,7 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re return addr; } +#ifdef CONFIG_MODIFY_LDT_SYSCALL /* * We'll assume that the code segments in the GDT * are all zero-based. That is largely true: the @@ -45,6 +46,7 @@ unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *re } mutex_unlock(&child->mm->context.lock); } +#endif return addr; } diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 7995ef5868d8..ca7d84f438f1 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -140,6 +140,7 @@ cond_syscall(sys_sgetmask); cond_syscall(sys_ssetmask); cond_syscall(sys_vm86old); cond_syscall(sys_vm86); +cond_syscall(sys_modify_ldt); cond_syscall(sys_ipc); cond_syscall(compat_sys_ipc); cond_syscall(compat_sys_sysctl); |