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Subject[PATCH v9 3/8] arm64: untag user addresses in access_ok and __uaccess_mask_ptr
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,
before performing access validity checks.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
arch/arm64/include/asm/uaccess.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 3c3864ba3cc1..d28c3b1314ce 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -104,7 +104,8 @@ 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) \
@@ -236,7 +237,8 @@ static inline void uaccess_enable_not_uao(void)

/*
* Sanitise a uaccess pointer such that it becomes NULL if above the
- * current addr_limit.
+ * current addr_limit. In case the pointer is tagged (has the top byte set),
+ * untag the pointer before checking.
*/
#define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
@@ -244,10 +246,11 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
void __user *safe_ptr;

asm volatile(
- " bics xzr, %1, %2\n"
+ " bics xzr, %3, %2\n"
" csel %0, %1, xzr, eq\n"
: "=&r" (safe_ptr)
- : "r" (ptr), "r" (current_thread_info()->addr_limit)
+ : "r" (ptr), "r" (current_thread_info()->addr_limit),
+ "r" (untagged_addr(ptr))
: "cc");

csdb();
--
2.20.0.rc2.403.gdbc3b29805-goog
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