linux-kernel - [PATCH 5.16 013/200] ARM: 9179/1: uaccess: avoid alignment faults in copy_[from|to]_kernel

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Message-Id: <20220131105234.006919976@linuxfoundation.org>
Date:   Mon, 31 Jan 2022 11:54:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Subject: [PATCH 5.16 013/200] ARM: 9179/1: uaccess: avoid alignment faults in copy_[from|to]_kernel_nofault

From: Ard Biesheuvel <ardb@...nel.org>

commit 15420269b02a63ed8c1841905d8b8b2403246004 upstream.

The helpers that are used to implement copy_from_kernel_nofault() and
copy_to_kernel_nofault() cast a void* to a pointer to a wider type,
which may result in alignment faults on ARM if the compiler decides to
use double-word or multiple-word load/store instructions.

Only configurations that define CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y
are affected, given that commit 2423de2e6f4d ("ARM: 9115/1: mm/maccess:
fix unaligned copy_{from,to}_kernel_nofault") ensures that dst and src
are sufficiently aligned otherwise.

So use the unaligned accessors for accessing dst and src in cases where
they may be misaligned.

Cc: <stable@...r.kernel.org> # depends on 2423de2e6f4d
Fixes: 2df4c9a741a0 ("ARM: 9112/1: uaccess: add __{get,put}_kernel_nofault")
Reviewed-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm/include/asm/uaccess.h |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -11,6 +11,7 @@
 #include <linux/string.h>
 #include <asm/memory.h>
 #include <asm/domain.h>
+#include <asm/unaligned.h>
 #include <asm/unified.h>
 #include <asm/compiler.h>
 
@@ -497,7 +498,10 @@ do {									\
 	}								\
 	default: __err = __get_user_bad(); break;			\
 	}								\
-	*(type *)(dst) = __val;						\
+	if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))		\
+		put_unaligned(__val, (type *)(dst));			\
+	else								\
+		*(type *)(dst) = __val; /* aligned by caller */		\
 	if (__err)							\
 		goto err_label;						\
 } while (0)
@@ -507,7 +511,9 @@ do {									\
 	const type *__pk_ptr = (dst);					\
 	unsigned long __dst = (unsigned long)__pk_ptr;			\
 	int __err = 0;							\
-	type __val = *(type *)src;					\
+	type __val = IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)	\
+		     ? get_unaligned((type *)(src))			\
+		     : *(type *)(src);	/* aligned by caller */		\
 	switch (sizeof(type)) {						\
 	case 1: __put_user_asm_byte(__val, __dst, __err, ""); break;	\
 	case 2:	__put_user_asm_half(__val, __dst, __err, ""); break;	\