[PATCH v4 3/5] signal: Add unsafe_copy_siginfo_to_user()

[Christophe Leroy]

In the same spirit as commit fb05121fd6a2 ("signal: Add
unsafe_get_compat_sigset()"), implement an 'unsafe' version of
copy_siginfo_to_user() in order to use it within user access blocks.

For that, also add an 'unsafe' version of clear_user().

This commit adds the generic fallback for unsafe_clear_user().
Architectures wanting to use unsafe_copy_siginfo_to_user() within a
user_access_begin() section have to make sure they have their
own unsafe_clear_user().

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
v3: Added precision about unsafe_clear_user() in commit message.
---
 include/linux/signal.h  | 15 +++++++++++++++
 include/linux/uaccess.h |  1 +
 kernel/signal.c         |  5 -----
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index 3f96a6374e4f..70ea7e741427 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -35,6 +35,21 @@ static inline void copy_siginfo_to_external(siginfo_t *to,
 int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from);
 int copy_siginfo_from_user(kernel_siginfo_t *to, const siginfo_t __user *from);
 
+static __always_inline char __user *si_expansion(const siginfo_t __user *info)
+{
+	return ((char __user *)info) + sizeof(struct kernel_siginfo);
+}
+
+#define unsafe_copy_siginfo_to_user(to, from, label) do {		\
+	siginfo_t __user *__ucs_to = to;				\
+	const kernel_siginfo_t *__ucs_from = from;			\
+	char __user *__ucs_expansion = si_expansion(__ucs_to);		\
+									\
+	unsafe_copy_to_user(__ucs_to, __ucs_from,			\
+			    sizeof(struct kernel_siginfo), label);	\
+	unsafe_clear_user(__ucs_expansion, SI_EXPANSION_SIZE, label);	\
+} while (0)
+
 enum siginfo_layout {
 	SIL_KILL,
 	SIL_TIMER,
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index c05e903cef02..37073caac474 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -398,6 +398,7 @@ long strnlen_user_nofault(const void __user *unsafe_addr, long count);
 #define unsafe_put_user(x,p,e) unsafe_op_wrap(__put_user(x,p),e)
 #define unsafe_copy_to_user(d,s,l,e) unsafe_op_wrap(__copy_to_user(d,s,l),e)
 #define unsafe_copy_from_user(d,s,l,e) unsafe_op_wrap(__copy_from_user(d,s,l),e)
+#define unsafe_clear_user(d, l, e) unsafe_op_wrap(__clear_user(d, l), e)
 static inline unsigned long user_access_save(void) { return 0UL; }
 static inline void user_access_restore(unsigned long flags) { }
 #endif
diff --git a/kernel/signal.c b/kernel/signal.c
index 952741f6d0f9..23f168730b7e 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3324,11 +3324,6 @@ enum siginfo_layout siginfo_layout(unsigned sig, int si_code)
 	return layout;
 }
 
-static inline char __user *si_expansion(const siginfo_t __user *info)
-{
-	return ((char __user *)info) + sizeof(struct kernel_siginfo);
-}
-
 int copy_siginfo_to_user(siginfo_t __user *to, const kernel_siginfo_t *from)
 {
 	char __user *expansion = si_expansion(to);
-- 
2.31.1