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From: Helge Deller <deller@gmx.de>
To: linux-parisc@vger.kernel.org,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	John David Anglin <dave.anglin@bell.net>,
	Sven Schnelle <svens@stackframe.org>
Subject: [PATCH] parisc: Fix user access miscompilation
Date: Wed, 9 Feb 2022 19:24:14 +0100	[thread overview]
Message-ID: <YgQGzle/mBRK9lBc@p100> (raw)

After commit 4b9d2a731c3d ("parisc: Switch user access functions
to signal errors in r29 instead of r8") bash suddenly started
to report those warnings after login:

-bash: cannot set terminal process group (-1): Bad file descriptor
-bash: no job control in this shell

It turned out, that another function call inside a put_user(), e.g.:
  put_user(vt_do_kdgkbmode(console), (int __user *)arg);
clobbered the error register (r29) and thus failed.
Avoid this miscompilation by first calculate the value in
__put_user() before calling __put_user_internal() to actually
write the value to user space.

Additionally, prefer the "+" constraint on pu_err and gu_err registers to tell
the compiler that those operands are both read and written by the assembly
instruction.

Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 4b9d2a731c3d ("parisc: Switch user access functions to signal errors in r29 instead of r8")

diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index ebf8a845b017..68f5c1eaaa6f 100644
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -89,7 +89,7 @@ struct exception_table_entry {
 	__asm__("1: " ldx " 0(" sr "%2),%0\n"		\
 		"9:\n"					\
 		ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b)	\
-		: "=r"(__gu_val), "=r"(__gu_err)        \
+		: "=&r"(__gu_val), "+r"(__gu_err)        \
 		: "r"(ptr), "1"(__gu_err));		\
 							\
 	(val) = (__force __typeof__(*(ptr))) __gu_val;	\
@@ -123,7 +123,7 @@ struct exception_table_entry {
 		"9:\n"					\
 		ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b)	\
 		ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b)	\
-		: "=&r"(__gu_tmp.l), "=r"(__gu_err)	\
+		: "=&r"(__gu_tmp.l), "+r"(__gu_err)	\
 		: "r"(ptr), "1"(__gu_err));		\
 							\
 	(val) = __gu_tmp.t;				\
@@ -132,10 +132,9 @@ struct exception_table_entry {
 #endif /* !defined(CONFIG_64BIT) */


-#define __put_user_internal(sr, x, ptr)				\
+#define __put_user_internal(sr, __x, ptr)			\
 ({								\
 	ASM_EXCEPTIONTABLE_VAR(__pu_err);		      	\
-        __typeof__(*(ptr)) __x = (__typeof__(*(ptr)))(x);	\
 								\
 	switch (sizeof(*(ptr))) {				\
 	case 1: __put_user_asm(sr, "stb", __x, ptr); break;	\
@@ -150,7 +149,9 @@ struct exception_table_entry {

 #define __put_user(x, ptr)					\
 ({								\
-	__put_user_internal("%%sr3,", x, ptr);			\
+	 __typeof__(*(ptr)) __x = (__typeof__(*(ptr)))(x);	\
+								\
+	__put_user_internal("%%sr3,", __x, ptr);		\
 })

 #define __put_kernel_nofault(dst, src, type, err_label)		\
@@ -180,7 +181,7 @@ struct exception_table_entry {
 		"1: " stx " %2,0(" sr "%1)\n"			\
 		"9:\n"						\
 		ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b)		\
-		: "=r"(__pu_err)				\
+		: "+r"(__pu_err)				\
 		: "r"(ptr), "r"(x), "0"(__pu_err))


@@ -193,7 +194,7 @@ struct exception_table_entry {
 		"9:\n"						\
 		ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 9b)		\
 		ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 9b)		\
-		: "=r"(__pu_err)				\
+		: "+r"(__pu_err)				\
 		: "r"(ptr), "r"(__val), "0"(__pu_err));		\
 } while (0)


             reply	other threads:[~2022-02-09 18:29 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-09 18:24 Helge Deller [this message]
2022-02-10 10:26 ` [PATCH] parisc: Fix user access miscompilation John David Anglin
2022-02-10 10:56   ` Helge Deller

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