Commit 15420269 authored Jan 18, 2022 by Ard Biesheuvel Committed by Russell King (Oracle) Jan 19, 2022

ARM: 9179/1: uaccess: avoid alignment faults in copy_[from|to]_kernel_nofault



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 2423de2e ("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@vger.kernel.org> # depends on 2423de2e
Fixes: 2df4c9a7 ("ARM: 9112/1: uaccess: add __{get,put}_kernel_nofault")
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

parent 8b59b0a5

arch/arm/include/asm/uaccess.h

+8 −2

Original line number	Diff line number	Diff line
		@@ -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; \