From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
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>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
---
v1:
- Update static asserts for NSIGSEGV
Yu-cheng v29:
- Remove pr_emerg() since it is followed by die().
- Change boot_cpu_has() to cpu_feature_enabled().
Yu-cheng v25:
- Change CONFIG_X86_CET to CONFIG_X86_SHADOW_STACK.
- Change X86_FEATURE_CET to X86_FEATURE_SHSTK.
arch/arm/kernel/signal.c | 2 +-
arch/arm64/kernel/signal.c | 2 +-
arch/arm64/kernel/signal32.c | 2 +-
arch/sparc/kernel/signal32.c | 2 +-
arch/sparc/kernel/signal_64.c | 2 +-
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 | 62 ++++++++++++++++++++++++++++++
include/uapi/asm-generic/siginfo.h | 3 +-
10 files changed, 78 insertions(+), 7 deletions(-)
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index c532a6041066..59aaadce9d52 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -681,7 +681,7 @@ asmlinkage void do_rseq_syscall(struct pt_regs *regs)
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
-static_assert(NSIGSEGV == 9);
+static_assert(NSIGSEGV == 10);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index d8aaf4b6f432..d2da57c415b8 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -983,7 +983,7 @@ void __init minsigstksz_setup(void)
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
-static_assert(NSIGSEGV == 9);
+static_assert(NSIGSEGV == 10);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index d984282b979f..8776a34c6444 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -460,7 +460,7 @@ void compat_setup_restart_syscall(struct pt_regs *regs)
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
-static_assert(NSIGSEGV == 9);
+static_assert(NSIGSEGV == 10);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
diff --git a/arch/sparc/kernel/signal32.c b/arch/sparc/kernel/signal32.c
index 6cc124a3bb98..dc50b2a78692 100644
--- a/arch/sparc/kernel/signal32.c
+++ b/arch/sparc/kernel/signal32.c
@@ -752,7 +752,7 @@ asmlinkage int do_sys32_sigstack(u32 u_ssptr, u32 u_ossptr, unsigned long sp)
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
-static_assert(NSIGSEGV == 9);
+static_assert(NSIGSEGV == 10);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
diff --git a/arch/sparc/kernel/signal_64.c b/arch/sparc/kernel/signal_64.c
index 2a78d2af1265..7fe2bd37bd1a 100644
--- a/arch/sparc/kernel/signal_64.c
+++ b/arch/sparc/kernel/signal_64.c
@@ -562,7 +562,7 @@ void do_notify_resume(struct pt_regs *regs, unsigned long orig_i0, unsigned long
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
-static_assert(NSIGSEGV == 9);
+static_assert(NSIGSEGV == 10);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 1345088e9902..a90791433152 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -562,6 +562,10 @@ 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_SHADOW_STACK
+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 df0fa695bb09..9f1bdaabc246 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -113,6 +113,10 @@ static const __initconst struct idt_data def_idts[] = {
#elif defined(CONFIG_X86_32)
SYSG(IA32_SYSCALL_VECTOR, entry_INT80_32),
#endif
+
+#ifdef CONFIG_X86_SHADOW_STACK
+ 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 b52407c56000..ff50cd978ea5 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 != 9);
+ BUILD_BUG_ON(NSIGSEGV != 10);
BUILD_BUG_ON(NSIGBUS != 5);
BUILD_BUG_ON(NSIGTRAP != 6);
BUILD_BUG_ON(NSIGCHLD != 6);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c9d566dcf89a..54b7a146fd5e 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -39,6 +39,7 @@
#include <linux/io.h>
#include <linux/hardirq.h>
#include <linux/atomic.h>
+#include <linux/nospec.h>
#include <asm/stacktrace.h>
#include <asm/processor.h>
@@ -641,6 +642,67 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
cond_local_irq_disable(regs);
}
+#ifdef CONFIG_X86_SHADOW_STACK
+static const char * const control_protection_err[] = {
+ "unknown",
+ "near-ret",
+ "far-ret/iret",
+ "endbranch",
+ "rstorssp",
+ "setssbsy",
+ "unknown",
+};
+
+static DEFINE_RATELIMIT_STATE(cpf_rate, DEFAULT_RATELIMIT_INTERVAL,
+ DEFAULT_RATELIMIT_BURST);
+
+/*
+ * When a control protection exception occurs, send a signal to the responsible
+ * application. Currently, control protection is only enabled for user mode.
+ * This exception should not come from kernel mode.
+ */
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
+{
+ struct task_struct *tsk;
+
+ if (!user_mode(regs)) {
+ die("kernel control protection fault", regs, error_code);
+ panic("Unexpected kernel control protection fault. Machine halted.");
+ }
+
+ cond_local_irq_enable(regs);
+
+ if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+ WARN_ONCE(1, "Control protection fault with CET support disabled\n");
+
+ tsk = current;
+ tsk->thread.error_code = error_code;
+ tsk->thread.trap_nr = X86_TRAP_CP;
+
+ /*
+ * Ratelimit to prevent log spamming.
+ */
+ if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
+ __ratelimit(&cpf_rate)) {
+ unsigned long ssp;
+ int cpf_type;
+
+ cpf_type = array_index_nospec(error_code, ARRAY_SIZE(control_protection_err));
+
+ rdmsrl(MSR_IA32_PL3_SSP, ssp);
+ pr_emerg("%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[cpf_type]);
+ print_vma_addr(KERN_CONT " in ", regs->ip);
+ pr_cont("\n");
+ }
+
+ force_sig_fault(SIGSEGV, SEGV_CPERR, (void __user *)0);
+ 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 3ba180f550d7..081f4b37d22c 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -240,7 +240,8 @@ typedef struct siginfo {
#define SEGV_ADIPERR 7 /* Precise MCD exception */
#define SEGV_MTEAERR 8 /* Asynchronous ARM MTE error */
#define SEGV_MTESERR 9 /* Synchronous ARM MTE exception */
-#define NSIGSEGV 9
+#define SEGV_CPERR 10 /* Control protection fault */
+#define NSIGSEGV 10
/*
* SIGBUS si_codes
--
2.17.1
