[RFC 1/3] x86/signal: add SA_{X32,IA32}_ABI sa_flags

[Dmitry Safonov]

Introduce new flags that defines which ABI to use on creating sigframe.
Those flags one may set from the userspace, or kernel will set them
according to syscall, which sets handler for a signal.
So that will drop the dependency on TIF_IA32/TIF_X32 flags on syscall deliver.
Those flags will be used only under CONFIG_COMPAT.

The same way ARM uses sa_flags to differ in which mode deliver signal
for 26-bit applications (look at SA_THIRYTWO).

Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
---
 arch/x86/ia32/ia32_signal.c        |  2 +-
 arch/x86/include/asm/fpu/signal.h  |  6 ++++++
 arch/x86/include/uapi/asm/signal.h |  6 +++++-
 arch/x86/kernel/signal.c           | 19 ++++++++++---------
 arch/x86/kernel/signal_compat.c    | 33 ++++++++++++++++++++++++++++++---
 kernel/signal.c                    |  5 +++++
 6 files changed, 57 insertions(+), 14 deletions(-)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 0552884da18d..faf1871300cb 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -378,7 +378,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
 		put_user_ex(*((u64 *)&code), (u64 __user *)frame->retcode);
 	} put_user_catch(err);
 
-	err |= copy_siginfo_to_user32(&frame->info, &ksig->info);
+	err |= __copy_siginfo_to_user32(&frame->info, &ksig->info, false);
 	err |= ia32_setup_sigcontext(&frame->uc.uc_mcontext, fpstate,
 				     regs, set->sig[0]);
 	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
diff --git a/arch/x86/include/asm/fpu/signal.h b/arch/x86/include/asm/fpu/signal.h
index 0e970d00dfcd..20a1fbf7fe4e 100644
--- a/arch/x86/include/asm/fpu/signal.h
+++ b/arch/x86/include/asm/fpu/signal.h
@@ -19,6 +19,12 @@ int ia32_setup_frame(int sig, struct ksignal *ksig,
 # define ia32_setup_rt_frame	__setup_rt_frame
 #endif
 
+#ifdef CONFIG_COMPAT
+int __copy_siginfo_to_user32(compat_siginfo_t __user *to,
+		const siginfo_t *from, bool x32_ABI);
+#endif
+
+
 extern void convert_from_fxsr(struct user_i387_ia32_struct *env,
 			      struct task_struct *tsk);
 extern void convert_to_fxsr(struct task_struct *tsk,
diff --git a/arch/x86/include/uapi/asm/signal.h b/arch/x86/include/uapi/asm/signal.h
index 8264f47cf53e..9c663b6fc023 100644
--- a/arch/x86/include/uapi/asm/signal.h
+++ b/arch/x86/include/uapi/asm/signal.h
@@ -70,6 +70,8 @@ typedef unsigned long sigset_t;
  * SA_RESETHAND clears the handler when the signal is delivered.
  * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies.
  * SA_NODEFER prevents the current signal from being masked in the handler.
+ * SA_IA32_ABI/SA_X32_ABI indicates ABI for a signal frame,
+ *   if neither is set, the kernel will set them according to a syscall ABI
  *
  * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
  * Unix names RESETHAND and NODEFER respectively.
@@ -85,7 +87,9 @@ typedef unsigned long sigset_t;
 #define SA_NOMASK	SA_NODEFER
 #define SA_ONESHOT	SA_RESETHAND
 
-#define SA_RESTORER	0x04000000
+#define SA_RESTORER	0x04000000u
+#define SA_IA32_ABI	0x02000000u
+#define SA_X32_ABI	0x01000000u
 
 #define MINSIGSTKSZ	2048
 #define SIGSTKSZ	8192
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index aa31265aa61d..8d13556f7df2 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -548,7 +548,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
 		return -EFAULT;
 
 	if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
-		if (copy_siginfo_to_user32(&frame->info, &ksig->info))
+		if (__copy_siginfo_to_user32(&frame->info, &ksig->info, true))
 			return -EFAULT;
 	}
 
@@ -661,20 +661,21 @@ badframe:
 	return 0;
 }
 
-static inline int is_ia32_compat_frame(void)
+static inline int is_ia32_compat_frame(struct ksignal *ksig)
 {
 	return config_enabled(CONFIG_IA32_EMULATION) &&
-	       test_thread_flag(TIF_IA32);
+		ksig->ka.sa.sa_flags & SA_IA32_ABI;
 }
 
-static inline int is_ia32_frame(void)
+static inline int is_ia32_frame(struct ksignal *ksig)
 {
-	return config_enabled(CONFIG_X86_32) || is_ia32_compat_frame();
+	return config_enabled(CONFIG_X86_32) || is_ia32_compat_frame(ksig);
 }
 
-static inline int is_x32_frame(void)
+static inline int is_x32_frame(struct ksignal *ksig)
 {
-	return config_enabled(CONFIG_X86_X32_ABI) && test_thread_flag(TIF_X32);
+	return config_enabled(CONFIG_X86_X32_ABI) &&
+		ksig->ka.sa.sa_flags & SA_X32_ABI;
 }
 
 static int
@@ -685,12 +686,12 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
 	compat_sigset_t *cset = (compat_sigset_t *) set;
 
 	/* Set up the stack frame */
-	if (is_ia32_frame()) {
+	if (is_ia32_frame(ksig)) {
 		if (ksig->ka.sa.sa_flags & SA_SIGINFO)
 			return ia32_setup_rt_frame(usig, ksig, cset, regs);
 		else
 			return ia32_setup_frame(usig, ksig, cset, regs);
-	} else if (is_x32_frame()) {
+	} else if (is_x32_frame(ksig)) {
 		return x32_setup_rt_frame(ksig, cset, regs);
 	} else {
 		return __setup_rt_frame(ksig->sig, ksig, set, regs);
diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index dc3c0b1c816f..7f2d7c784a47 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c
@@ -1,10 +1,31 @@
 #include <linux/compat.h>
 #include <linux/uaccess.h>
+#include <linux/ptrace.h>
 
-int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
+void sigaction_compat_abi(struct k_sigaction *act)
+{
+	if (!act)
+		return;
+
+	/* don't let to set both ABI flags */
+	if (act->sa.sa_flags & SA_IA32_ABI && act->sa.sa_flags & SA_X32_ABI)
+		act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
+
+	if (user_64bit_mode(current_pt_regs()))
+		return;
+
+	if (!(act->sa.sa_flags & (SA_IA32_ABI | SA_X32_ABI))) {
+		if (in_ia32_syscall())
+			act->sa.sa_flags |= SA_IA32_ABI;
+		if (in_x32_syscall())
+			act->sa.sa_flags |= SA_X32_ABI;
+	}
+}
+
+int __copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from,
+		bool x32_ABI)
 {
 	int err = 0;
-	bool ia32 = test_thread_flag(TIF_IA32);
 
 	if (!access_ok(VERIFY_WRITE, to, sizeof(compat_siginfo_t)))
 		return -EFAULT;
@@ -38,7 +59,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 				put_user_ex(from->si_arch, &to->si_arch);
 				break;
 			case __SI_CHLD >> 16:
-				if (ia32) {
+				if (!x32_ABI) {
 					put_user_ex(from->si_utime, &to->si_utime);
 					put_user_ex(from->si_stime, &to->si_stime);
 				} else {
@@ -72,6 +93,12 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 	return err;
 }
 
+/* from syscall's path, where we know the ABI */
+int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
+{
+	return __copy_siginfo_to_user32(to, from, in_x32_syscall());
+}
+
 int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
 {
 	int err = 0;
diff --git a/kernel/signal.c b/kernel/signal.c
index aa9bf00749c1..d0309f2a36f0 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3048,6 +3048,10 @@ void kernel_sigaction(int sig, __sighandler_t action)
 }
 EXPORT_SYMBOL(kernel_sigaction);
 
+void __weak sigaction_compat_abi(struct k_sigaction *act)
+{
+}
+
 int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 {
 	struct task_struct *p = current, *t;
@@ -3058,6 +3062,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 		return -EINVAL;
 
 	k = &p->sighand->action[sig-1];
+	sigaction_compat_abi(act);
 
 	spin_lock_irq(&p->sighand->siglock);
 	if (oact)
-- 
2.8.0