This allows userspace to detect missing support for flag bits and
allows the kernel to use non-uapi bits internally, as we are already
doing in arch/x86 for two flag bits. Now that this change is in
place, we no longer need the code in arch/x86 that was hiding these
bits from userspace, so remove it.

Signed-off-by: Peter Collingbourne <redacted>
---
View this change in Gerrit: https://linux-review.googlesource.com/q/I35aab6f5be932505d90f3b3450c083b4db1eca86

 arch/arm/include/asm/signal.h    |  4 ++++
 arch/parisc/include/asm/signal.h |  4 ++++
 arch/x86/kernel/signal_compat.c  |  7 -------
 include/linux/signal_types.h     | 12 ++++++++++++
 kernel/signal.c                  | 10 ++++++++++
 5 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/arch/arm/include/asm/signal.h b/arch/arm/include/asm/signal.h
index 65530a042009..d1070a783993 100644
--- a/arch/arm/include/asm/signal.h
+++ b/arch/arm/include/asm/signal.h

@@ -17,6 +17,10 @@ typedef struct {
 	unsigned long sig[_NSIG_WORDS];
 } sigset_t;
 
+#define SA_UAPI_FLAGS                                                          \
+	(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_THIRTYTWO |             \
+	 SA_RESTORER | SA_ONSTACK | SA_RESTART | SA_NODEFER | SA_RESETHAND)
+

 #define __ARCH_HAS_SA_RESTORER
 
 #include <asm/sigcontext.h>

diff --git a/arch/parisc/include/asm/signal.h b/arch/parisc/include/asm/signal.h
index 715c96ba2ec8..ad06e14f6e8a 100644
--- a/arch/parisc/include/asm/signal.h
+++ b/arch/parisc/include/asm/signal.h

@@ -21,6 +21,10 @@ typedef struct {
 	unsigned long sig[_NSIG_WORDS];
 } sigset_t;
 
+#define SA_UAPI_FLAGS                                                          \
+	(SA_ONSTACK | SA_RESETHAND | SA_NOCLDSTOP | SA_SIGINFO | SA_NODEFER |  \
+	 SA_RESTART | SA_NOCLDWAIT | _SA_SIGGFAULT)
+
 #include <asm/sigcontext.h>
 
 #endif /* !__ASSEMBLY */

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index 9ccbf0576cd0..c599013ae8cb 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/arch/x86/kernel/signal_compat.c

@@ -165,16 +165,9 @@ void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
 {
 	signal_compat_build_tests();
 
-	/* Don't leak in-kernel non-uapi flags to user-space */
-	if (oact)
-		oact->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
-
 	if (!act)
 		return;
 
-	/* Don't let flags to be set from userspace */
-	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())

diff --git a/include/linux/signal_types.h b/include/linux/signal_types.h
index f8a90ae9c6ec..e792f29b5846 100644
--- a/include/linux/signal_types.h
+++ b/include/linux/signal_types.h

@@ -68,4 +68,16 @@ struct ksignal {
 	int sig;
 };
 
+#ifndef SA_UAPI_FLAGS
+#ifdef SA_RESTORER
+#define SA_UAPI_FLAGS                                                          \
+	(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART |  \
+	 SA_NODEFER | SA_RESETHAND | SA_RESTORER)
+#else
+#define SA_UAPI_FLAGS                                                          \
+	(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART |  \
+	 SA_NODEFER | SA_RESETHAND)
+#endif
+#endif
+
 #endif /* _LINUX_SIGNAL_TYPES_H */

diff --git a/kernel/signal.c b/kernel/signal.c
index 42b67d2cea37..348b7981f1ff 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c

@@ -3984,6 +3984,16 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 	if (oact)
 		*oact = *k;
 
+	/*
+	 * Clear unknown flag bits in order to allow userspace to detect missing
+	 * support for flag bits and to allow the kernel to use non-uapi bits
+	 * internally.
+	 */
+	if (act)
+		act->sa.sa_flags &= SA_UAPI_FLAGS;
+	if (oact)
+		oact->sa.sa_flags &= SA_UAPI_FLAGS;
+