---

yaml
---
r: 277447
b: refs/heads/master
c: 4fc3490
h: refs/heads/master
i:
  277445: a231ffd
  277443: d94dfe0
  277439: 273101f
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 01acc269083015e2f78407f59dc8d6378fce22ee
+refs/heads/master: 4fc3490114bb159bd4fff1b3c96f4320fe6fb08f

trunk/arch/x86/include/asm/thread_info.h

@@ -40,7 +40,8 @@ struct thread_info {
 						*/
 	__u8			supervisor_stack[0];
 #endif
-	int			uaccess_err;
+	int			sig_on_uaccess_error:1;
+	int			uaccess_err:1;	/* uaccess failed */
 };
 
 #define INIT_THREAD_INFO(tsk)			\

trunk/arch/x86/include/asm/uaccess.h

@@ -462,7 +462,7 @@ struct __large_struct { unsigned long buf[100]; };
 	barrier();
 
 #define uaccess_catch(err)						\
-	(err) |= current_thread_info()->uaccess_err;			\
+	(err) |= (current_thread_info()->uaccess_err ? -EFAULT : 0);	\
 	current_thread_info()->uaccess_err = prev_err;			\
 } while (0)
 

trunk/arch/x86/kernel/vsyscall_64.c

@@ -140,11 +140,40 @@ static int addr_to_vsyscall_nr(unsigned long addr)
 	return nr;
 }
 
+static bool write_ok_or_segv(unsigned long ptr, size_t size)
+{
+	/*
+	 * XXX: if access_ok, get_user, and put_user handled
+	 * sig_on_uaccess_error, this could go away.
+	 */
+
+	if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
+		siginfo_t info;
+		struct thread_struct *thread = &current->thread;
+
+		thread->error_code	= 6;  /* user fault, no page, write */
+		thread->cr2		= ptr;
+		thread->trap_no		= 14;
+
+		memset(&info, 0, sizeof(info));
+		info.si_signo		= SIGSEGV;
+		info.si_errno		= 0;
+		info.si_code		= SEGV_MAPERR;
+		info.si_addr		= (void __user *)ptr;
+
+		force_sig_info(SIGSEGV, &info, current);
+		return false;
+	} else {
+		return true;
+	}
+}
+
 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 {
 	struct task_struct *tsk;
 	unsigned long caller;
 	int vsyscall_nr;
+	int prev_sig_on_uaccess_error;
 	long ret;
 
 	/*
@@ -180,35 +209,65 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 	if (seccomp_mode(&tsk->seccomp))
 		do_exit(SIGKILL);
 
+	/*
+	 * With a real vsyscall, page faults cause SIGSEGV.  We want to
+	 * preserve that behavior to make writing exploits harder.
+	 */
+	prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
+	current_thread_info()->sig_on_uaccess_error = 1;
+
+	/*
+	 * 0 is a valid user pointer (in the access_ok sense) on 32-bit and
+	 * 64-bit, so we don't need to special-case it here.  For all the
+	 * vsyscalls, 0 means "don't write anything" not "write it at
+	 * address 0".
+	 */
+	ret = -EFAULT;
 	switch (vsyscall_nr) {
 	case 0:
+		if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
+		    !write_ok_or_segv(regs->si, sizeof(struct timezone)))
+			break;
+
 		ret = sys_gettimeofday(
 			(struct timeval __user *)regs->di,
 			(struct timezone __user *)regs->si);
 		break;
 
 	case 1:
+		if (!write_ok_or_segv(regs->di, sizeof(time_t)))
+			break;
+
 		ret = sys_time((time_t __user *)regs->di);
 		break;
 
 	case 2:
+		if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
+		    !write_ok_or_segv(regs->si, sizeof(unsigned)))
+			break;
+
 		ret = sys_getcpu((unsigned __user *)regs->di,
 				 (unsigned __user *)regs->si,
 				 0);
 		break;
 	}
 
+	current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
+
 	if (ret == -EFAULT) {
-		/*
-		 * Bad news -- userspace fed a bad pointer to a vsyscall.
-		 *
-		 * With a real vsyscall, that would have caused SIGSEGV.
-		 * To make writing reliable exploits using the emulated
-		 * vsyscalls harder, generate SIGSEGV here as well.
-		 */
+		/* Bad news -- userspace fed a bad pointer to a vsyscall. */
 		warn_bad_vsyscall(KERN_INFO, regs,
 				  "vsyscall fault (exploit attempt?)");
-		goto sigsegv;
+
+		/*
+		 * If we failed to generate a signal for any reason,
+		 * generate one here.  (This should be impossible.)
+		 */
+		if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
+				 !sigismember(&tsk->pending.signal, SIGSEGV)))
+			goto sigsegv;
+
+		return true;  /* Don't emulate the ret. */
 	}
 
 	regs->ax = ret;

trunk/arch/x86/mm/extable.c

@@ -25,7 +25,7 @@ int fixup_exception(struct pt_regs *regs)
 	if (fixup) {
 		/* If fixup is less than 16, it means uaccess error */
 		if (fixup->fixup < 16) {
-			current_thread_info()->uaccess_err = -EFAULT;
+			current_thread_info()->uaccess_err = 1;
 			regs->ip += fixup->fixup;
 			return 1;
 		}

trunk/arch/x86/mm/fault.c

@@ -626,16 +626,25 @@ pgtable_bad(struct pt_regs *regs, unsigned long error_code,
 
 static noinline void
 no_context(struct pt_regs *regs, unsigned long error_code,
-	   unsigned long address)
+	   unsigned long address, int signal, int si_code)
 {
 	struct task_struct *tsk = current;
 	unsigned long *stackend;
 	unsigned long flags;
 	int sig;
 
 	/* Are we prepared to handle this kernel fault? */
-	if (fixup_exception(regs))
+	if (fixup_exception(regs)) {
+		if (current_thread_info()->sig_on_uaccess_error && signal) {
+			tsk->thread.trap_no = 14;
+			tsk->thread.error_code = error_code | PF_USER;
+			tsk->thread.cr2 = address;
+
+			/* XXX: hwpoison faults will set the wrong code. */
+			force_sig_info_fault(signal, si_code, address, tsk, 0);
+		}
 		return;
+	}
 
 	/*
 	 * 32-bit:
@@ -755,7 +764,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 	if (is_f00f_bug(regs, address))
 		return;
 
-	no_context(regs, error_code, address);
+	no_context(regs, error_code, address, SIGSEGV, si_code);
 }
 
 static noinline void
@@ -819,7 +828,7 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
 
 	/* Kernel mode? Handle exceptions or die: */
 	if (!(error_code & PF_USER)) {
-		no_context(regs, error_code, address);
+		no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
 		return;
 	}
 
@@ -854,7 +863,7 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
 		if (!(fault & VM_FAULT_RETRY))
 			up_read(&current->mm->mmap_sem);
 		if (!(error_code & PF_USER))
-			no_context(regs, error_code, address);
+			no_context(regs, error_code, address, 0, 0);
 		return 1;
 	}
 	if (!(fault & VM_FAULT_ERROR))
@@ -864,7 +873,8 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
 		/* Kernel mode? Handle exceptions or die: */
 		if (!(error_code & PF_USER)) {
 			up_read(&current->mm->mmap_sem);
-			no_context(regs, error_code, address);
+			no_context(regs, error_code, address,
+				   SIGSEGV, SEGV_MAPERR);
 			return 1;
 		}