[RFC PATCH v1 17/19] signal: Add unsafe_put_compat_sigset()

[Christophe Leroy]

Implement 'unsafe' version of put_compat_sigset()

For the bigendian, use unsafe_put_user() directly
to avoid intermediate copy through the stack.

For the littleendian, use a straight unsafe_copy_to_user().

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Dmitry V. Levin <ldv@xxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
 include/linux/compat.h | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/include/linux/compat.h b/include/linux/compat.h
index c4255d8a4a8a..bbe5f9658ed1 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -442,6 +442,38 @@ put_compat_sigset(compat_sigset_t __user *compat, const sigset_t *set,
 #endif
 }
 
+#ifdef CONFIG_CPU_BIG_ENDIAN
+#define unsafe_put_compat_sigset(compat, set, label) do { 		\
+	compat_sigset_t __user *__c = compat;				\
+	const sigset_t *__s = set;					\
+									\
+	switch (_NSIG_WORDS) {						\
+	case 4:								\
+		unsafe_put_user(__s->sig[3] >> 32, __c->sig[7], label);	\
+		unsafe_put_user(__s->sig[3], __c->sig[6], label);	\
+		fallthrough;						\
+	case 3:								\
+		unsafe_put_user(__s->sig[2] >> 32, __c->sig[5], label);	\
+		unsafe_put_user(__s->sig[2], __c->sig[4], label);	\
+		fallthrough;						\
+	case 2:								\
+		unsafe_put_user(__s->sig[1] >> 32, __c->sig[3], label);	\
+		unsafe_put_user(__s->sig[1], __c->sig[2], label);	\
+		fallthrough;						\
+	case 1:								\
+		unsafe_put_user(__s->sig[0] >> 32, __c->sig[1], label);	\
+		unsafe_put_user(__s->sig[0], __c->sig[0], label);	\
+	}								\
+} while (0)
+#else
+#define unsafe_put_compat_sigset(compat, set, label) do { 		\
+	compat_sigset_t __user *__c = compat;				\
+	const sigset_t *__s = set;					\
+									\
+	unsafe_copy_to_user(__c, __s, sizeof(*__c), label);		\
+} while (0)
+#endif
+
 extern int compat_ptrace_request(struct task_struct *child,
 				 compat_long_t request,
 				 compat_ulong_t addr, compat_ulong_t data);
-- 
2.25.0