| Message ID | 20180921150351.20898-7-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Control Flow Enforcement: Shadow Stack | expand |
On Fri, Sep 21, 2018 at 08:03:30AM -0700, Yu-cheng Yu wrote: > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index e6db475164ed..873765adc244 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -578,6 +578,64 @@ do_general_protection(struct pt_regs *regs, long error_code) > } > NOKPROBE_SYMBOL(do_general_protection); > > +static const char *control_protection_err[] = > +{ > + "unknown", > + "near-ret", > + "far-ret/iret", > + "endbranch", > + "rstorssp", > + "setssbsy", > +}; > + > +/* > + * When a control protection exception occurs, send a signal > + * to the responsible application. Currently, control > + * protection is only enabled for the user mode. This > + * exception should not come from the kernel mode. > + */ > +dotraplinkage void > +do_control_protection(struct pt_regs *regs, long error_code) > +{ > + struct task_struct *tsk; > + > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + if (notify_die(DIE_TRAP, "control protection fault", regs, > + error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP) > + return; > + cond_local_irq_enable(regs); > + > + if (!user_mode(regs)) > + die("kernel control protection fault", regs, error_code); > + > + if (!static_cpu_has(X86_FEATURE_SHSTK) && > + !static_cpu_has(X86_FEATURE_IBT)) > + WARN_ONCE(1, "CET is disabled but got control " > + "protection fault\n"); > + > + tsk = current; > + tsk->thread.error_code = error_code; > + tsk->thread.trap_nr = X86_TRAP_CP; > + > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && > + printk_ratelimit()) { > + unsigned int max_err; > + > + max_err = ARRAY_SIZE(control_protection_err) - 1; > + if ((error_code < 0) || (error_code > max_err)) > + error_code = 0; > + pr_info("%s[%d] control protection ip:%lx sp:%lx error:%lx(%s)", > + tsk->comm, task_pid_nr(tsk), > + regs->ip, regs->sp, error_code, > + control_protection_err[error_code]); > + print_vma_addr(KERN_CONT " in ", regs->ip); > + pr_cont("\n"); > + } > + > + force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk); That way, no information is provided to userspace (both application and debugger), which is rather unfortunate. It would be nice if a new SEGV_* code was added at least, and CET error (with error code constant provided in UAPI) is passed via si_errno. (Having ip/sp/*ssp would be even better, but I'm not exactly sure about ramifications of providing this kind of information to user space).
On Wed, 2018-10-03 at 12:39 +0200, Eugene Syromiatnikov wrote: > On Fri, Sep 21, 2018 at 08:03:30AM -0700, Yu-cheng Yu wrote: > > +dotraplinkage void > > +do_control_protection(struct pt_regs *regs, long error_code) > > +{ > > + struct task_struct *tsk; > > + > > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > > + if (notify_die(DIE_TRAP, "control protection fault", regs, > > + error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP) > > + return; > > + cond_local_irq_enable(regs); > > + > > + if (!user_mode(regs)) > > + die("kernel control protection fault", regs, error_code); > > + > > + if (!static_cpu_has(X86_FEATURE_SHSTK) && > > + !static_cpu_has(X86_FEATURE_IBT)) > > + WARN_ONCE(1, "CET is disabled but got control " > > + "protection fault\n"); > > + > > + tsk = current; > > + tsk->thread.error_code = error_code; > > + tsk->thread.trap_nr = X86_TRAP_CP; > > + > > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && > > + printk_ratelimit()) { > > + unsigned int max_err; > > + > > + max_err = ARRAY_SIZE(control_protection_err) - 1; > > + if ((error_code < 0) || (error_code > max_err)) > > + error_code = 0; > > + pr_info("%s[%d] control protection ip:%lx sp:%lx > > error:%lx(%s)", > > + tsk->comm, task_pid_nr(tsk), > > + regs->ip, regs->sp, error_code, > > + control_protection_err[error_code]); > > + print_vma_addr(KERN_CONT " in ", regs->ip); > > + pr_cont("\n"); > > + } > > + > > + force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk); > > That way, no information is provided to userspace (both application and > debugger), which is rather unfortunate. It would be nice if a new SEGV_* > code was added at least, and CET error (with error code constant provided > in UAPI) is passed via si_errno. (Having ip/sp/*ssp would be even > better, but I'm not exactly sure about ramifications of providing this > kind of information to user space). Ok, I will add that. Yu-cheng
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 957dfb693ecc..5f4914e988df 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1000,7 +1000,7 @@ idtentry spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0 idtentry coprocessor_error do_coprocessor_error has_error_code=0 idtentry alignment_check do_alignment_check has_error_code=1 idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0 - +idtentry control_protection do_control_protection has_error_code=1 /* * Reload gs selector with exception handling diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h index 3de69330e6c5..5196050ff3d5 100644 --- a/arch/x86/include/asm/traps.h +++ b/arch/x86/include/asm/traps.h @@ -26,6 +26,7 @@ asmlinkage void invalid_TSS(void); asmlinkage void segment_not_present(void); asmlinkage void stack_segment(void); asmlinkage void general_protection(void); +asmlinkage void control_protection(void); asmlinkage void page_fault(void); asmlinkage void async_page_fault(void); asmlinkage void spurious_interrupt_bug(void); @@ -77,6 +78,7 @@ dotraplinkage void do_stack_segment(struct pt_regs *, long); dotraplinkage void do_double_fault(struct pt_regs *, long); #endif dotraplinkage void do_general_protection(struct pt_regs *, long); +dotraplinkage void do_control_protection(struct pt_regs *, long); dotraplinkage void do_page_fault(struct pt_regs *, unsigned long); dotraplinkage void do_spurious_interrupt_bug(struct pt_regs *, long); dotraplinkage void do_coprocessor_error(struct pt_regs *, long); @@ -142,6 +144,7 @@ enum { X86_TRAP_AC, /* 17, Alignment Check */ X86_TRAP_MC, /* 18, Machine Check */ X86_TRAP_XF, /* 19, SIMD Floating-Point Exception */ + X86_TRAP_CP = 21, /* 21 Control Protection Fault */ X86_TRAP_IRET = 32, /* 32, IRET Exception */ }; diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c index 01adea278a71..66ebc8cb16e2 100644 --- a/arch/x86/kernel/idt.c +++ b/arch/x86/kernel/idt.c @@ -104,6 +104,10 @@ static const __initconst struct idt_data def_idts[] = { #elif defined(CONFIG_X86_32) SYSG(IA32_SYSCALL_VECTOR, entry_INT80_32), #endif + +#ifdef CONFIG_X86_64 + INTG(X86_TRAP_CP, control_protection), +#endif }; /* diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index e6db475164ed..873765adc244 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -578,6 +578,64 @@ do_general_protection(struct pt_regs *regs, long error_code) } NOKPROBE_SYMBOL(do_general_protection); +static const char *control_protection_err[] = +{ + "unknown", + "near-ret", + "far-ret/iret", + "endbranch", + "rstorssp", + "setssbsy", +}; + +/* + * When a control protection exception occurs, send a signal + * to the responsible application. Currently, control + * protection is only enabled for the user mode. This + * exception should not come from the kernel mode. + */ +dotraplinkage void +do_control_protection(struct pt_regs *regs, long error_code) +{ + struct task_struct *tsk; + + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); + if (notify_die(DIE_TRAP, "control protection fault", regs, + error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP) + return; + cond_local_irq_enable(regs); + + if (!user_mode(regs)) + die("kernel control protection fault", regs, error_code); + + if (!static_cpu_has(X86_FEATURE_SHSTK) && + !static_cpu_has(X86_FEATURE_IBT)) + WARN_ONCE(1, "CET is disabled but got control " + "protection fault\n"); + + tsk = current; + tsk->thread.error_code = error_code; + tsk->thread.trap_nr = X86_TRAP_CP; + + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && + printk_ratelimit()) { + unsigned int max_err; + + max_err = ARRAY_SIZE(control_protection_err) - 1; + if ((error_code < 0) || (error_code > max_err)) + error_code = 0; + pr_info("%s[%d] control protection ip:%lx sp:%lx error:%lx(%s)", + tsk->comm, task_pid_nr(tsk), + regs->ip, regs->sp, error_code, + control_protection_err[error_code]); + print_vma_addr(KERN_CONT " in ", regs->ip); + pr_cont("\n"); + } + + force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk); +} +NOKPROBE_SYMBOL(do_control_protection); + dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code) { #ifdef CONFIG_DYNAMIC_FTRACE
A control protection exception is triggered when a control flow transfer attempt violated shadow stack or indirect branch tracking constraints. For example, the return address for a RET instruction differs from the safe copy on the shadow stack; or a JMP instruction arrives at a non- ENDBR instruction. The control protection exception handler works in a similar way as the general protection fault handler. Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> --- arch/x86/entry/entry_64.S | 2 +- arch/x86/include/asm/traps.h | 3 ++ arch/x86/kernel/idt.c | 4 +++ arch/x86/kernel/traps.c | 58 ++++++++++++++++++++++++++++++++++++ 4 files changed, 66 insertions(+), 1 deletion(-)