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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id e4sm3563052pgi.80.2019.06.07.20.51.09 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 07 Jun 2019 20:51:09 -0700 (PDT) Date: Fri, 7 Jun 2019 20:51:08 -0700 From: Kees Cook To: Andrey Konovalov Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Catalin Marinas , Vincenzo Frascino , Will Deacon , Mark Rutland , Andrew Morton , Greg Kroah-Hartman , Yishai Hadas , Felix Kuehling , Alexander Deucher , Christian Koenig , Mauro Carvalho Chehab , Jens Wiklander , Alex Williamson , Leon Romanovsky , Luc Van Oostenryck , Dave Martin , Khalid Aziz , enh , Jason Gunthorpe , Christoph Hellwig , Dmitry Vyukov , Kostya Serebryany , Evgeniy Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Robin Murphy , Kevin Brodsky , Szabolcs Nagy Subject: Re: [PATCH v16 02/16] arm64: untag user pointers in access_ok and __uaccess_mask_ptr Message-ID: <201906072051.3047B3DC56@keescook> References: <4327b260fb17c4776a1e3c844f388e4948cfb747.1559580831.git.andreyknvl@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4327b260fb17c4776a1e3c844f388e4948cfb747.1559580831.git.andreyknvl@google.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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 > Signed-off-by: Andrey Konovalov Reviewed-by: Kees Cook -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