On 12/06/2019 12:43, Andrey Konovalov wrote:
This patch is a part of a series that extends arm64 kernel ABI to allow to pass tagged user pointers (with the top byte set to something else other than 0x00) as syscall arguments.
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.
Note, that this patch only temporarily untags the pointers to perform the checks, but then passes them as is into the kernel internals.
Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Andrey Konovalov andreyknvl@google.com
Reviewed-by: Vincenzo Frascino vincenzo.frascino@arm.com
arch/arm64/include/asm/uaccess.h | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index e5d5f31c6d36..df729afca0ba 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -73,6 +73,8 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si { unsigned long ret, limit = current_thread_info()->addr_limit;
- addr = untagged_addr(addr);
- __chk_user_ptr(addr); asm volatile( // A + B <= C + 1 for all A,B,C, in four easy steps:
@@ -226,7 +228,8 @@ 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) @@ -234,10 +237,11 @@ 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))csdb();