From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Garnier Subject: Re: [PATCH v2 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state Date: Thu, 9 Mar 2017 07:56:49 -0800 Message-ID: References: <20170309012456.5631-1-thgarnie@google.com> <20170309012456.5631-4-thgarnie@google.com> <20170309122354.GB6320@leverpostej> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20170309122354.GB6320@leverpostej> To: Mark Rutland Cc: David Howells , Dave Hansen , Arnd Bergmann , Al Viro , =?UTF-8?Q?Ren=C3=A9_Nyffenegger?= , Andrew Morton , Kees Cook , "Paul E . McKenney" , "David S . Miller" , Andy Lutomirski , Ard Biesheuvel , Nicolas Pitre , Petr Mladek , Sebastian Andrzej Siewior , Sergey Senozhatsky , Helge Deller , Rik van Riel , Ingo Molnar , Oleg Nesterov , John Stultz , Thomas Gleixner , Pavel Tikhomirov List-Id: linux-api@vger.kernel.org On Thu, Mar 9, 2017 at 4:23 AM, Mark Rutland wrote: > We generally stick to lower case for the arm64 assembly macros. If we > need this, we should stick to the existing convention. > >> +/* Similar to set_fs(USER_DS) in verify_pre_usermode_state without a warning. */ >> +.macro VERIFY_PRE_USERMODE_STATE >> + mov x1, #TASK_SIZE_64 >> + str x1, [tsk, #TSK_TI_ADDR_LIMIT] >> +.endm > > We need arm64's set_fs() to configure UAO, too, so this is much weaker > than set_fs(), and will leave __{get,put}_user and > __copy_{to,from}_user() able to access kernel memory. > > We don't currently have an asm helper to clear UAO, and unconditionally > poking that on exception return is liable to be somewhat expensive. > > Also, given we're only trying to catch this in syscalls, I'm afraid I > don't see what we gain by doing this in the entry assembly. > I optimized all architectures from the arm (32-bit) discussion. I will come back to a simple bl to the verify function. Thanks! -- Thomas