diff options
| -rw-r--r-- | arch/x86/kernel/ptrace.c | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 96286df1bb8..702c33efea8 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -103,9 +103,26 @@ static int set_segment_reg(struct task_struct *task, if (invalid_selector(value)) return -EIO; - if (offset != offsetof(struct user_regs_struct, gs)) + /* + * For %cs and %ss we cannot permit a null selector. + * We can permit a bogus selector as long as it has USER_RPL. + * Null selectors are fine for other segment registers, but + * we will never get back to user mode with invalid %cs or %ss + * and will take the trap in iret instead. Much code relies + * on user_mode() to distinguish a user trap frame (which can + * safely use invalid selectors) from a kernel trap frame. + */ + switch (offset) { + case offsetof(struct user_regs_struct, cs): + case offsetof(struct user_regs_struct, ss): + if (unlikely(value == 0)) + return -EIO; + + default: *pt_regs_access(task_pt_regs(task), offset) = value; - else { + break; + + case offsetof(struct user_regs_struct, gs): task->thread.gs = value; if (task == current) /* @@ -227,12 +244,16 @@ static int set_segment_reg(struct task_struct *task, * Can't actually change these in 64-bit mode. */ case offsetof(struct user_regs_struct,cs): + if (unlikely(value == 0)) + return -EIO; #ifdef CONFIG_IA32_EMULATION if (test_tsk_thread_flag(task, TIF_IA32)) task_pt_regs(task)->cs = value; #endif break; case offsetof(struct user_regs_struct,ss): + if (unlikely(value == 0)) + return -EIO; #ifdef CONFIG_IA32_EMULATION if (test_tsk_thread_flag(task, TIF_IA32)) task_pt_regs(task)->ss = value; |