kernel: add ksys_personality()

Using this helper allows us to avoid the in-kernel call to the
sys_personality() syscall. The ksys_ prefix denotes that this function
is meant as a drop-in replacement for the syscall. In particular, it
uses the same calling convention as sys_personality().

Since ksys_personality is trivial, it is implemented directly in
<linux/syscalls.h>, as we do for ksys_close() and friends.

This helper is necessary to enable conversion of arm64's syscall
handling to use pt_regs wrappers.

Signed-off-by: Mark Rutland <[email protected]>
Reviewed-by: Dominik Brodowski <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Dave Martin <[email protected]>
Signed-off-by: Will Deacon <[email protected]>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a368a68cb667..abfe12d8a9c5 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -80,6 +80,7 @@ union bpf_attr;
 #include <linux/unistd.h>
 #include <linux/quota.h>
 #include <linux/key.h>
+#include <linux/personality.h>
 #include <trace/syscall.h>
 
 #ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
@@ -1281,4 +1282,14 @@ static inline long ksys_truncate(const char __user *pathname, loff_t length)
 	return do_sys_truncate(pathname, length);
 }
 
+static inline unsigned int ksys_personality(unsigned int personality)
+{
+	unsigned int old = current->personality;
+
+	if (personality != 0xffffffff)
+		set_personality(personality);
+
+	return old;
+}
+
 #endif