A control-protection fault is triggered when a control-flow transfer
attempt violates Shadow Stack or Indirect Branch Tracking constraints.
For example, the return address for a RET instruction differs from the copy
on the Shadow Stack; or an indirect JMP instruction, without the NOTRACK
prefix, arrives at a non-ENDBR opcode.
The control-protection fault handler works in a similar way as the general
protection fault handler. It provides the si_code SEGV_CPERR to the signal
handler.
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
arch/x86/include/asm/idtentry.h | 4 ++
arch/x86/kernel/idt.c | 4 ++
arch/x86/kernel/signal_compat.c | 2 +-
arch/x86/kernel/traps.c | 59 ++++++++++++++++++++++++++++++
include/uapi/asm-generic/siginfo.h | 3 +-
5 files changed, 70 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index a0638640f1ed..3130a6ec0a2a 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -532,6 +532,10 @@ DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_SS, exc_stack_segment);
DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_GP, exc_general_protection);
DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_AC, exc_alignment_check);
+#ifdef CONFIG_X86_CET
+DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_CP, exc_control_protection);
+#endif
+
/* Raw exception entries which need extra work */
DECLARE_IDTENTRY_RAW(X86_TRAP_UD, exc_invalid_op);
DECLARE_IDTENTRY_RAW(X86_TRAP_BP, exc_int3);
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 7ecf9babf0cb..34f2a7383d5d 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -112,6 +112,10 @@ static const __initconst struct idt_data def_idts[] = {
#elif defined(CONFIG_X86_32)
SYSG(IA32_SYSCALL_VECTOR, entry_INT80_32),
#endif
+
+#ifdef CONFIG_X86_CET
+ INTG(X86_TRAP_CP, asm_exc_control_protection),
+#endif
};
/*
diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index 9ccbf0576cd0..c572a3de1037 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -27,7 +27,7 @@ static inline void signal_compat_build_tests(void)
*/
BUILD_BUG_ON(NSIGILL != 11);
BUILD_BUG_ON(NSIGFPE != 15);
- BUILD_BUG_ON(NSIGSEGV != 7);
+ BUILD_BUG_ON(NSIGSEGV != 8);
BUILD_BUG_ON(NSIGBUS != 5);
BUILD_BUG_ON(NSIGTRAP != 5);
BUILD_BUG_ON(NSIGCHLD != 6);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 81a2fb711091..97a049258e33 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -597,6 +597,65 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
cond_local_irq_disable(regs);
}
+#ifdef CONFIG_X86_CET
+static const char * const 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.
+ */
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
+{
+ struct task_struct *tsk;
+
+ 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;
+ unsigned long ssp;
+
+ max_err = ARRAY_SIZE(control_protection_err) - 1;
+ if ((error_code < 0) || (error_code > max_err))
+ error_code = 0;
+ rdmsrl(MSR_IA32_PL3_SSP, ssp);
+ pr_info("%s[%d] control protection ip:%lx sp:%lx ssp:%lx error:%lx(%s)",
+ tsk->comm, task_pid_nr(tsk),
+ regs->ip, regs->sp, ssp, error_code,
+ control_protection_err[error_code]);
+ print_vma_addr(KERN_CONT " in ", regs->ip);
+ pr_cont("\n");
+ }
+
+ force_sig_fault(SIGSEGV, SEGV_CPERR,
+ (void __user *)uprobe_get_trap_addr(regs));
+ cond_local_irq_disable(regs);
+}
+#endif
+
static bool do_int3(struct pt_regs *regs)
{
int res;
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index cb3d6c267181..91e10cbe3bb0 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -229,7 +229,8 @@ typedef struct siginfo {
#define SEGV_ACCADI 5 /* ADI not enabled for mapped object */
#define SEGV_ADIDERR 6 /* Disrupting MCD error */
#define SEGV_ADIPERR 7 /* Precise MCD exception */
-#define NSIGSEGV 7
+#define SEGV_CPERR 8 /* Control protection fault */
+#define NSIGSEGV 8
/*
* SIGBUS si_codes
--
2.21.0
