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[217.140.110.172]) by mx.google.com with ESMTP id t16si2773199edd.443.2019.06.13.08.46.02 for ; Thu, 13 Jun 2019 08:46:02 -0700 (PDT) Received-SPF: pass (google.com: domain of vincenzo.frascino@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vincenzo.frascino@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=vincenzo.frascino@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 35647367; Thu, 13 Jun 2019 08:46:01 -0700 (PDT) Received: from [10.1.196.72] (e119884-lin.cambridge.arm.com [10.1.196.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA3A53F246; Thu, 13 Jun 2019 08:45:55 -0700 (PDT) Subject: Re: [PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI To: Catalin Marinas , Dave Martin Cc: Andrey Konovalov , 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, Mark Rutland , Szabolcs Nagy , Will Deacon , Kostya Serebryany , Khalid Aziz , Felix Kuehling , Jacob Bramley , Leon Romanovsky , Christoph Hellwig , Jason Gunthorpe , Evgeniy Stepanov , Kevin Brodsky , Kees Cook , Ruben Ayrapetyan , Ramana Radhakrishnan , Alex Williamson , Mauro Carvalho Chehab , Dmitry Vyukov , Greg Kroah-Hartman , Yishai Hadas , Jens Wiklander , Lee Smith , Alexander Deucher , Andrew Morton , enh , Robin Murphy , Christian Koenig , Luc Van Oostenryck References: <20190613111659.GX28398@e103592.cambridge.arm.com> <20190613153505.GU28951@C02TF0J2HF1T.local> From: Vincenzo Frascino Message-ID: <99cc257d-5e99-922a-fbe7-3bbaf3621e38@arm.com> Date: Thu, 13 Jun 2019 16:45:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190613153505.GU28951@C02TF0J2HF1T.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 13/06/2019 16:35, Catalin Marinas wrote: > On Thu, Jun 13, 2019 at 12:16:59PM +0100, Dave P Martin wrote: >> On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote: >>> From: Catalin Marinas >>> >>> It is not desirable to relax the ABI to allow tagged user addresses into >>> the kernel indiscriminately. This patch introduces a prctl() interface >>> for enabling or disabling the tagged ABI with a global sysctl control >>> for preventing applications from enabling the relaxed ABI (meant for >>> testing user-space prctl() return error checking without reconfiguring >>> the kernel). The ABI properties are inherited by threads of the same >>> application and fork()'ed children but cleared on execve(). >>> >>> The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle >>> MTE-specific settings like imprecise vs precise exceptions. >>> >>> Signed-off-by: Catalin Marinas >>> --- >>> arch/arm64/include/asm/processor.h | 6 +++ >>> arch/arm64/include/asm/thread_info.h | 1 + >>> arch/arm64/include/asm/uaccess.h | 3 +- >>> arch/arm64/kernel/process.c | 67 ++++++++++++++++++++++++++++ >>> include/uapi/linux/prctl.h | 5 +++ >>> kernel/sys.c | 16 +++++++ >>> 6 files changed, 97 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h >>> index fcd0e691b1ea..fee457456aa8 100644 >>> --- a/arch/arm64/include/asm/processor.h >>> +++ b/arch/arm64/include/asm/processor.h >>> @@ -307,6 +307,12 @@ extern void __init minsigstksz_setup(void); >>> /* PR_PAC_RESET_KEYS prctl */ >>> #define PAC_RESET_KEYS(tsk, arg) ptrauth_prctl_reset_keys(tsk, arg) >>> >>> +/* PR_TAGGED_ADDR prctl */ >> >> (A couple of comments I missed in my last reply:) >> >> Name mismatch? > > Yeah, it went through several names but it seems that I didn't update > all places. > >>> +long set_tagged_addr_ctrl(unsigned long arg); >>> +long get_tagged_addr_ctrl(void); >>> +#define SET_TAGGED_ADDR_CTRL(arg) set_tagged_addr_ctrl(arg) >>> +#define GET_TAGGED_ADDR_CTRL() get_tagged_addr_ctrl() >>> + >> >> [...] >> >>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c >>> index 3767fb21a5b8..69d0be1fc708 100644 >>> --- a/arch/arm64/kernel/process.c >>> +++ b/arch/arm64/kernel/process.c >>> @@ -30,6 +30,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> #include >>> @@ -323,6 +324,7 @@ void flush_thread(void) >>> fpsimd_flush_thread(); >>> tls_thread_flush(); >>> flush_ptrace_hw_breakpoint(current); >>> + clear_thread_flag(TIF_TAGGED_ADDR); >>> } >>> >>> void release_thread(struct task_struct *dead_task) >>> @@ -552,3 +554,68 @@ void arch_setup_new_exec(void) >>> >>> ptrauth_thread_init_user(current); >>> } >>> + >>> +/* >>> + * Control the relaxed ABI allowing tagged user addresses into the kernel. >>> + */ >>> +static unsigned int tagged_addr_prctl_allowed = 1; >>> + >>> +long set_tagged_addr_ctrl(unsigned long arg) >>> +{ >>> + if (!tagged_addr_prctl_allowed) >>> + return -EINVAL; >> >> So, tagging can actually be locked on by having a process enable it and >> then some possibly unrelated process clearing tagged_addr_prctl_allowed. >> That feels a bit weird. > > The problem is that if you disable the ABI globally, lots of > applications would crash. This sysctl is meant as a way to disable the > opt-in to the TBI ABI. Another option would be a kernel command line > option (I'm not keen on a Kconfig option). > Why you are not keen on a Kconfig option? >> Do we want to allow a process that has tagging on to be able to turn >> it off at all? Possibly things like CRIU might want to do that. > > I left it in for symmetry but I don't expect it to be used. A potential > use-case is doing it per subsequent threads in an application. > >>> + if (is_compat_task()) >>> + return -EINVAL; >>> + if (arg & ~PR_TAGGED_ADDR_ENABLE) >>> + return -EINVAL; >> >> How do we expect this argument to be extended in the future? > > Yes, for MTE. That's why I wouldn't allow random bits here. > >> I'm wondering whether this is really a bitmask or an enum, or a mixture >> of the two. Maybe it doesn't matter. > > User may want to set PR_TAGGED_ADDR_ENABLE | PR_MTE_PRECISE in a single > call. > >>> + if (arg & PR_TAGGED_ADDR_ENABLE) >>> + set_thread_flag(TIF_TAGGED_ADDR); >>> + else >>> + clear_thread_flag(TIF_TAGGED_ADDR); >> >> I think update_thread_flag() could be used here. > > Yes. I forgot you added this. > -- Regards, Vincenzo