Messages in this thread Patch in this message | | | Date | Tue, 23 Jul 2019 19:58:38 +0200 | Subject | [PATCH v19 01/15] arm64: untag user pointers in access_ok and __uaccess_mask_ptr | From | Andrey Konovalov <> |
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This patch is a part of a series that extends 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: Vincenzo Frascino <vincenzo.frascino@arm.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Andrey Konovalov <andreyknvl@google.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 5a1c32260c1f..a138e3b4f717 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -62,6 +62,8 @@ 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: @@ -215,7 +217,8 @@ 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) @@ -223,10 +226,11 @@ 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(); -- 2.22.0.709.g102302147b-goog
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