linux-kernel - [PATCH 4/5] x86: asm: make sure __put_user

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Message-ID: <20221024212144.2852069-4-glider@google.com>
Date:   Mon, 24 Oct 2022 23:21:43 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     glider@...gle.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        youling257 <youling257@...il.com>
Subject: [PATCH 4/5] x86: asm: make sure __put_user_size() evaluates pointer once

User access macros must ensure their arguments are evaluated only once
if they are used more than once in the macro body. Adding
instrument_put_user() to __put_user_size() resulted in double evaluation
of the `ptr` argument, which led to correctness issues when performing
e.g. unsafe_put_user(..., p++, ...).
To fix those issues, evaluate the `ptr` argument of __put_user_size()
at the beginning of the macro.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
Reported-by: youling257 <youling257@...il.com>
Signed-off-by: Alexander Potapenko <glider@...gle.com>
Fixes: 888f84a6da4d ("x86: asm: instrument usercopy in get_user() and put_user()")
---
 arch/x86/include/asm/uaccess.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 8bc614cfe21b9..1cc756eafa447 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -254,24 +254,25 @@ extern void __put_user_nocheck_8(void);
 #define __put_user_size(x, ptr, size, label)				\
 do {									\
 	__typeof__(*(ptr)) __x = (x); /* eval x once */			\
-	__chk_user_ptr(ptr);						\
+	__typeof__(ptr) __ptr = (ptr); /* eval ptr once */		\
+	__chk_user_ptr(__ptr);						\
 	switch (size) {							\
 	case 1:								\
-		__put_user_goto(__x, ptr, "b", "iq", label);		\
+		__put_user_goto(__x, __ptr, "b", "iq", label);		\
 		break;							\
 	case 2:								\
-		__put_user_goto(__x, ptr, "w", "ir", label);		\
+		__put_user_goto(__x, __ptr, "w", "ir", label);		\
 		break;							\
 	case 4:								\
-		__put_user_goto(__x, ptr, "l", "ir", label);		\
+		__put_user_goto(__x, __ptr, "l", "ir", label);		\
 		break;							\
 	case 8:								\
-		__put_user_goto_u64(__x, ptr, label);			\
+		__put_user_goto_u64(__x, __ptr, label);			\
 		break;							\
 	default:							\
 		__put_user_bad();					\
 	}								\
-	instrument_put_user(__x, ptr, size);				\
+	instrument_put_user(__x, __ptr, size);				\
 } while (0)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-- 
2.38.0.135.g90850a2211-goog