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Subject[RFC PATCH v2 3/6] arm64: untag user addresses in copy_from_user and others
Date
copy_from_user (and a few other similar functions) are used to copy data
from user memory into the kernel memory or vice versa. Since a user can
provided a tagged pointer to one of the syscalls that use copy_from_user,
we need to correctly handle such pointers.

Do this by untagging user pointers in access_ok and in __uaccess_mask_ptr.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
arch/arm64/include/asm/uaccess.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 2d6451cbaa86..24a221678fe3 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -105,7 +105,8 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
#define untagged_addr(addr) \
((__typeof__(addr))sign_extend64((__u64)(addr), 55))

-#define access_ok(type, addr, size) __range_ok(addr, size)
+#define access_ok(type, addr, size) \
+ __range_ok(untagged_addr(addr), size)
#define user_addr_max get_fs

#define _ASM_EXTABLE(from, to) \
@@ -238,12 +239,15 @@ static inline void uaccess_enable_not_uao(void)
/*
* Sanitise a uaccess pointer such that it becomes NULL if above the
* current addr_limit.
+ * Also untag user pointers that have the top byte tag set.
*/
#define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
{
void __user *safe_ptr;

+ ptr = untagged_addr(ptr);
+
asm volatile(
" bics xzr, %1, %2\n"
" csel %0, %1, xzr, eq\n"
--
2.17.0.rc0.231.g781580f067-goog
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