arm64: uaccess: consistently check object sizes

Currently in arm64's copy_{to,from}_user, we only check the
source/destination object size if access_ok() tells us the user access
is permissible.

However, in copy_from_user() we'll subsequently zero any remainder on
the destination object. If we failed the access_ok() check, that applies
to the whole object size, which we didn't check.

To ensure that we catch that case, this patch hoists check_object_size()
to the start of copy_from_user(), matching __copy_from_user() and
__copy_to_user(). To make all of our uaccess copy primitives consistent,
the same is done to copy_to_user().

Cc: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 46da3ea638bbdfc858161f3e00ac560562692359..5308d696311bcdd130e98d316e9b902d5bb075f5 100644 (file)
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -379,9 +379,9 @@ static inline unsigned long __must_check copy_from_user(void *to, const void __u
 {
        unsigned long res = n;
        kasan_check_write(to, n);
+       check_object_size(to, n, false);
 
        if (access_ok(VERIFY_READ, from, n)) {
-               check_object_size(to, n, false);
                res = __arch_copy_from_user(to, from, n);
        }
        if (unlikely(res))
@@ -392,9 +392,9 @@ static inline unsigned long __must_check copy_from_user(void *to, const void __u
 static inline unsigned long __must_check copy_to_user(void __user *to, const void *from, unsigned long n)
 {
        kasan_check_read(from, n);
+       check_object_size(from, n, true);
 
        if (access_ok(VERIFY_WRITE, to, n)) {
-               check_object_size(from, n, true);
                n = __arch_copy_to_user(to, from, n);
        }
        return n;