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From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Shuah Khan <shuah@kernel.org>
Cc:     mhiramat@kernel.org, linux-kernel@vger.kernel.org,
        Andy Lutomirski <luto@amacapital.net>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Changbin Du <changbin.du@gmail.com>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Nadav Amit <namit@vmware.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Joel Fernandes <joel@joelfernandes.org>, yhs@fb.com
Subject: [PATCH v5 1/6] uaccess: Add user_access_ok()
Date:   Fri,  1 Mar 2019 01:02:55 +0900
Message-Id: <155136977556.2968.5821499627398165570.stgit@devbox>
In-Reply-To: <155136974478.2968.3105123100519786079.stgit@devbox>
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From: Peter Zijlstra <peterz@infradead.org>

Add user_access_ok() macro which ensures current context
is user context, or explicitly do set_fs(USER_DS).

This function is very much like access_ok(), except it (may)
have different context validation. In general we must be
very careful when using this.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 arch/x86/include/asm/uaccess.h |    8 +++++++-
 include/linux/uaccess.h        |   18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 780f2b42c8ef..3125d129d3b6 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -92,12 +92,18 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
  * checks that the pointer is in the user space range - after calling
  * this function, memory access functions may still return -EFAULT.
  */
-#define access_ok(addr, size)					\
+#define access_ok(addr, size)						\
 ({									\
 	WARN_ON_IN_IRQ();						\
 	likely(!__range_not_ok(addr, size, user_addr_max()));		\
 })
 
+#define user_access_ok(addr, size)					\
+({									\
+	WARN_ON_ONCE(!segment_eq(get_fs(), USER_DS));			\
+	likely(!__range_not_ok(addr, size, user_addr_max()));		\
+})
+
 /*
  * These are the main single-value transfer routines.  They automatically
  * use the right size if we just have the right pointer type.
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 37b226e8df13..bf762689658b 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -10,6 +10,24 @@
 
 #include <asm/uaccess.h>
 
+/**
+ * user_access_ok: Checks if a user space pointer is valid
+ * @addr: User space pointer to start of block to check
+ * @size: Size of block to check
+ *
+ * Context: User context or explicit set_fs(USER_DS).
+ *
+ * This function is very much like access_ok(), except it (may) have different
+ * context validation. In general we must be very careful when using this.
+ */
+#ifndef user_access_ok
+#define user_access_ok(addr, size)					\
+({									\
+	WARN_ON_ONCE(!segment_eq(get_fs(), USER_DS));			\
+	access_ok(addr, size);						\
+})
+#endif
+
 /*
  * Architectures should provide two primitives (raw_copy_{to,from}_user())
  * and get rid of their private instances of copy_{to,from}_user() and