On Mon, Jun 03, 2019 at 06:55:04PM +0200, 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: Catalin Marinas <catalin.marinas@xxxxxxx> > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -Kees > --- > arch/arm64/include/asm/uaccess.h | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > index e5d5f31c6d36..9164ecb5feca 100644 > --- a/arch/arm64/include/asm/uaccess.h > +++ b/arch/arm64/include/asm/uaccess.h > @@ -94,7 +94,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si > return ret; > } > > -#define access_ok(addr, size) __range_ok(addr, size) > +#define access_ok(addr, size) __range_ok(untagged_addr(addr), size) > #define user_addr_max get_fs > > #define _ASM_EXTABLE(from, to) \ > @@ -226,7 +226,8 @@ 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 +235,11 @@ 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.rc1.311.g5d7573a151-goog > -- Kees Cook
