[PATCH v2 04/20] x86: Rewrite copy_siginfo_{to,from}_user32

["Amanieu d'Antras" <amanieu@gmail.com>]

x86 can't use the generic versions because it needs to support
x32, so we replace the ad-hoc implementations with something
that is closer to the generic versions.

This is done by completely replacing the existing code with the
generic version, with some minor modifications to support x32.
The new code is kept as close as possible to the generic version
to make future changes to both functions easier.

Unlike the previous implementation, this one guarantees that the
compat behavior is identical to that of a 32-bit kernel.

Signed-off-by: Amanieu d'Antras <amanieu@gmail.com>
---
 arch/x86/kernel/signal_compat.c | 285 ++++++++++++++++++++++++++++++----------
 1 file changed, 214 insertions(+), 71 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index dc3c0b1..cdbb538 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -3,93 +3,236 @@
 
 int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 {
-	int err = 0;
+	int err, si_code;
 	bool ia32 = test_thread_flag(TIF_IA32);
 
 	if (!access_ok(VERIFY_WRITE, to, sizeof(compat_siginfo_t)))
 		return -EFAULT;
 
-	put_user_try {
-		/* If you change siginfo_t structure, please make sure that
-		   this code is fixed accordingly.
-		   It should never copy any pad contained in the structure
-		   to avoid security leaks, but must copy the generic
-		   3 ints plus the relevant union member.  */
-		put_user_ex(from->si_signo, &to->si_signo);
-		put_user_ex(from->si_errno, &to->si_errno);
-		put_user_ex((short)from->si_code, &to->si_code);
+	/*
+	 * Get the user-visible si_code by hiding the top 16 bits if this is a
+	 * kernel-generated signal.
+	 */
+	si_code = from->si_code < 0 ? from->si_code : (short)from->si_code;
 
-		if (from->si_code < 0) {
-			put_user_ex(from->si_pid, &to->si_pid);
-			put_user_ex(from->si_uid, &to->si_uid);
-			put_user_ex(ptr_to_compat(from->si_ptr), &to->si_ptr);
+	/*
+	 * If you change siginfo_t structure, please be sure that
+	 * all these functions are fixed accordingly:
+	 * copy_siginfo_to_user
+	 * copy_siginfo_to_user32
+	 * copy_siginfo_from_user32
+	 * signalfd_copyinfo
+	 * They should never copy any pad contained in the structure
+	 * to avoid security leaks, but must copy the generic
+	 * 3 ints plus the relevant union member.
+	 */
+	err = __put_user(from->si_signo, &to->si_signo);
+	err |= __put_user(from->si_errno, &to->si_errno);
+	err |= __put_user(si_code, &to->si_code);
+	if (from->si_code < 0) {
+		/*
+		 * Copy the tail bytes of the union from the padding, see the
+		 * comment in copy_siginfo_from_user32. Note that this padding
+		 * is always initialized when si_code < 0.
+		 */
+		BUILD_BUG_ON(sizeof(to->_sifields._pad) !=
+			sizeof(from->_sifields._pad) + sizeof(from->_pad2));
+		err |= __copy_to_user(to->_sifields._pad, from->_sifields._pad,
+			sizeof(from->_sifields._pad)) ? -EFAULT : 0;
+		err |= __copy_to_user(to->_sifields._pad + SI_PAD_SIZE,
+			from->_pad2, sizeof(from->_pad2)) ? -EFAULT : 0;
+		return err;
+	}
+	switch (from->si_code & __SI_MASK) {
+	case __SI_KILL:
+		err |= __put_user(from->si_pid, &to->si_pid);
+		err |= __put_user(from->si_uid, &to->si_uid);
+		break;
+	case __SI_TIMER:
+		err |= __put_user(from->si_tid, &to->si_tid);
+		err |= __put_user(from->si_overrun, &to->si_overrun);
+		/*
+		 * Get the sigval from si_int, which matches the convention
+		 * used in get_compat_sigevent.
+		 */
+		err |= __put_user(from->si_int, &to->si_int);
+		break;
+	case __SI_POLL:
+		err |= __put_user(from->si_band, &to->si_band);
+		err |= __put_user(from->si_fd, &to->si_fd);
+		break;
+	case __SI_FAULT:
+		err |= __put_user(ptr_to_compat(from->si_addr), &to->si_addr);
+#ifdef __ARCH_SI_TRAPNO
+		err |= __put_user(from->si_trapno, &to->si_trapno);
+#endif
+#ifdef BUS_MCEERR_AO
+		/*
+		 * Other callers might not initialize the si_lsb field,
+		 * so check explicitly for the right codes here.
+		 */
+		if (from->si_signo == SIGBUS &&
+		    (from->si_code == BUS_MCEERR_AR ||
+		     from->si_code == BUS_MCEERR_AO))
+			err |= __put_user(from->si_addr_lsb, &to->si_addr_lsb);
+#endif
+#ifdef SEGV_BNDERR
+		if (from->si_signo == SIGSEGV && from->si_code == SEGV_BNDERR) {
+			err |= __put_user(ptr_to_compat(from->si_lower),
+				&to->si_lower);
+			err |= __put_user(ptr_to_compat(from->si_upper),
+				&to->si_upper);
+		}
+#endif
+		break;
+	case __SI_CHLD:
+		err |= __put_user(from->si_pid, &to->si_pid);
+		err |= __put_user(from->si_uid, &to->si_uid);
+		err |= __put_user(from->si_status, &to->si_status);
+		if (ia32) {
+			err |= __put_user(from->si_utime, &to->si_utime);
+			err |= __put_user(from->si_stime, &to->si_stime);
 		} else {
-			/*
-			 * First 32bits of unions are always present:
-			 * si_pid === si_band === si_tid === si_addr(LS half)
-			 */
-			put_user_ex(from->_sifields._pad[0],
-					  &to->_sifields._pad[0]);
-			switch (from->si_code >> 16) {
-			case __SI_FAULT >> 16:
-				break;
-			case __SI_SYS >> 16:
-				put_user_ex(from->si_syscall, &to->si_syscall);
-				put_user_ex(from->si_arch, &to->si_arch);
-				break;
-			case __SI_CHLD >> 16:
-				if (ia32) {
-					put_user_ex(from->si_utime, &to->si_utime);
-					put_user_ex(from->si_stime, &to->si_stime);
-				} else {
-					put_user_ex(from->si_utime, &to->_sifields._sigchld_x32._utime);
-					put_user_ex(from->si_stime, &to->_sifields._sigchld_x32._stime);
-				}
-				put_user_ex(from->si_status, &to->si_status);
-				/* FALL THROUGH */
-			default:
-			case __SI_KILL >> 16:
-				put_user_ex(from->si_uid, &to->si_uid);
-				break;
-			case __SI_POLL >> 16:
-				put_user_ex(from->si_fd, &to->si_fd);
-				break;
-			case __SI_TIMER >> 16:
-				put_user_ex(from->si_overrun, &to->si_overrun);
-				put_user_ex(ptr_to_compat(from->si_ptr),
-					    &to->si_ptr);
-				break;
-				 /* This is not generated by the kernel as of now.  */
-			case __SI_RT >> 16:
-			case __SI_MESGQ >> 16:
-				put_user_ex(from->si_uid, &to->si_uid);
-				put_user_ex(from->si_int, &to->si_int);
-				break;
-			}
+			err |= __put_user(from->si_utime,
+				&to->_sifields._sigchld_x32._utime);
+			err |= __put_user(from->si_stime,
+				&to->_sifields._sigchld_x32._stime);
 		}
-	} put_user_catch(err);
-
+		break;
+	case __SI_RT: /* This is not generated by the kernel as of now. */
+	case __SI_MESGQ: /* But this is */
+		err |= __put_user(from->si_pid, &to->si_pid);
+		err |= __put_user(from->si_uid, &to->si_uid);
+		/*
+		 * Get the sigval from si_int, which matches the convention
+		 * used in get_compat_sigevent.
+		 */
+		err |= __put_user(from->si_int, &to->si_int);
+		break;
+#ifdef __ARCH_SIGSYS
+	case __SI_SYS:
+		err |= __put_user(ptr_to_compat(from->si_call_addr),
+			&to->si_call_addr);
+		err |= __put_user(from->si_syscall, &to->si_syscall);
+		err |= __put_user(from->si_arch, &to->si_arch);
+		break;
+#endif
+	default: /* this is just in case for now ... */
+		err |= __put_user(from->si_pid, &to->si_pid);
+		err |= __put_user(from->si_uid, &to->si_uid);
+		break;
+	}
 	return err;
 }
 
 int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
 {
-	int err = 0;
-	u32 ptr32;
+	int err;
+	compat_uptr_t ptr32;
+	bool ia32 = test_thread_flag(TIF_IA32);
 
 	if (!access_ok(VERIFY_READ, from, sizeof(compat_siginfo_t)))
 		return -EFAULT;
 
-	get_user_try {
-		get_user_ex(to->si_signo, &from->si_signo);
-		get_user_ex(to->si_errno, &from->si_errno);
-		get_user_ex(to->si_code, &from->si_code);
-
-		get_user_ex(to->si_pid, &from->si_pid);
-		get_user_ex(to->si_uid, &from->si_uid);
-		get_user_ex(ptr32, &from->si_ptr);
-		to->si_ptr = compat_ptr(ptr32);
-	} get_user_catch(err);
-
+	/*
+	 * If you change siginfo_t structure, please be sure that
+	 * all these functions are fixed accordingly:
+	 * copy_siginfo_to_user
+	 * copy_siginfo_to_user32
+	 * copy_siginfo_from_user32
+	 * signalfd_copyinfo
+	 * They should never copy any pad contained in the structure
+	 * to avoid security leaks, but must copy the generic
+	 * 3 ints plus the relevant union member.
+	 */
+	err = __get_user(to->si_signo, &from->si_signo);
+	err |= __get_user(to->si_errno, &from->si_errno);
+	err |= __get_user(to->si_code, &from->si_code);
+	if (to->si_code < 0) {
+		/*
+		 * Note that the compat union may be larger than the normal one
+		 * due to alignment. We work around this by copying any data
+		 * that doesn't fit in the normal union into the padding before
+		 * the union.
+		 */
+		BUILD_BUG_ON(sizeof(to->_sifields._pad) + sizeof(to->_pad2) !=
+			sizeof(from->_sifields._pad));
+		err |= __copy_from_user(to->_sifields._pad,
+			from->_sifields._pad,
+			sizeof(to->_sifields._pad)) ? -EFAULT : 0;
+		err |= __copy_from_user(to->_pad2,
+			from->_sifields._pad + SI_PAD_SIZE, sizeof(to->_pad2))
+			? -EFAULT : 0;
+		return err;
+	}
+	switch (to->si_code & __SI_MASK) {
+	case __SI_KILL:
+		err |= __get_user(to->si_pid, &from->si_pid);
+		err |= __get_user(to->si_uid, &from->si_uid);
+		break;
+	case __SI_TIMER:
+		err |= __get_user(to->si_tid, &from->si_tid);
+		err |= __get_user(to->si_overrun, &from->si_overrun);
+		/*
+		 * Put the sigval in si_int, which matches the convention
+		 * used in get_compat_sigevent.
+		 */
+		to->si_ptr = NULL; /* Avoid uninitialized bits in the union */
+		err |= __get_user(to->si_int, &from->si_int);
+		break;
+	case __SI_POLL:
+		err |= __get_user(to->si_band, &from->si_band);
+		err |= __get_user(to->si_fd, &from->si_fd);
+		break;
+	case __SI_FAULT:
+		err |= __get_user(ptr32, &from->si_addr);
+		to->si_addr = compat_ptr(ptr32);
+#ifdef __ARCH_SI_TRAPNO
+		err |= __get_user(to->si_trapno, &from->si_trapno);
+#endif
+		err |= __get_user(to->si_addr_lsb, &from->si_addr_lsb);
+		err |= __get_user(ptr32, &from->si_lower);
+		to->si_lower = compat_ptr(ptr32);
+		err |= __get_user(ptr32, &from->si_upper);
+		to->si_upper = compat_ptr(ptr32);
+		break;
+	case __SI_CHLD:
+		err |= __get_user(to->si_pid, &from->si_pid);
+		err |= __get_user(to->si_uid, &from->si_uid);
+		err |= __get_user(to->si_status, &from->si_status);
+		if (ia32) {
+			err |= __get_user(to->si_utime, &from->si_utime);
+			err |= __get_user(to->si_stime, &from->si_stime);
+		} else {
+			err |= __get_user(to->si_utime,
+				&from->_sifields._sigchld_x32._utime);
+			err |= __get_user(to->si_stime,
+				&from->_sifields._sigchld_x32._stime);
+		}
+		break;
+	case __SI_RT: /* This is not generated by the kernel as of now. */
+	case __SI_MESGQ: /* But this is */
+		err |= __get_user(to->si_pid, &from->si_pid);
+		err |= __get_user(to->si_uid, &from->si_uid);
+		/*
+		 * Put the sigval in si_int, which matches the convention
+		 * used in get_compat_sigevent.
+		 */
+		to->si_ptr = NULL; /* Avoid uninitialized bits in the union */
+		err |= __get_user(to->si_int, &from->si_int);
+		break;
+#ifdef __ARCH_SIGSYS
+	case __SI_SYS:
+		err |= __get_user(ptr32, &from->si_call_addr);
+		to->si_call_addr = compat_ptr(ptr32);
+		err |= __get_user(to->si_syscall, &from->si_syscall);
+		err |= __get_user(to->si_arch, &from->si_arch);
+		break;
+#endif
+	default: /* this is just in case for now ... */
+		err |= __get_user(to->si_pid, &from->si_pid);
+		err |= __get_user(to->si_uid, &from->si_uid);
+		break;
+	}
 	return err;
 }
-- 
2.6.2