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[217.140.101.70]) by mx.google.com with ESMTP id i23si551224ejv.131.2019.05.28.10.02.54 for ; Tue, 28 May 2019 10:02:55 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of catalin.marinas@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of catalin.marinas@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=catalin.marinas@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A5FEB341; Tue, 28 May 2019 10:02:53 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C71E83F59C; Tue, 28 May 2019 10:02:47 -0700 (PDT) Date: Tue, 28 May 2019 18:02:45 +0100 From: Catalin Marinas To: Kees Cook Cc: enh , Evgenii Stepanov , Andrey Konovalov , Khalid Aziz , Linux ARM , Linux Memory Management List , LKML , amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, "open list:KERNEL SELFTEST FRAMEWORK" , 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 , Dmitry Vyukov , Kostya Serebryany , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Robin Murphy , Luc Van Oostenryck , Dave Martin , Kevin Brodsky , Szabolcs Nagy Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel Message-ID: <20190528170244.GF32006@arrakis.emea.arm.com> References: <20190521182932.sm4vxweuwo5ermyd@mbp> <201905211633.6C0BF0C2@keescook> <20190522101110.m2stmpaj7seezveq@mbp> <20190522163527.rnnc6t4tll7tk5zw@mbp> <201905221316.865581CF@keescook> <20190523144449.waam2mkyzhjpqpur@mbp> <201905230917.DEE7A75EF0@keescook> <20190523174345.6sv3kcipkvlwfmox@mbp> <201905231327.77CA8D0A36@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201905231327.77CA8D0A36@keescook> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Thu, May 23, 2019 at 02:31:16PM -0700, Kees Cook wrote: > syzkaller already attempts to randomly inject non-canonical and > 0xFFFF....FFFF addresses for user pointers in syscalls in an effort to > find bugs like CVE-2017-5123 where waitid() via unchecked put_user() was > able to write directly to kernel memory[1]. > > It seems that using TBI by default and not allowing a switch back to > "normal" ABI without a reboot actually means that userspace cannot inject > kernel pointers into syscalls any more, since they'll get universally > stripped now. Is my understanding correct, here? i.e. exploiting > CVE-2017-5123 would be impossible under TBI? > > If so, then I think we should commit to the TBI ABI and have a boot > flag to disable it, but NOT have a process flag, as that would allow > attackers to bypass the masking. The only flag should be "TBI or MTE". > > If so, can I get top byte masking for other architectures too? Like, > just to strip high bits off userspace addresses? ;) Just for fun, hack/attempt at your idea which should not interfere with TBI. Only briefly tested on arm64 (and the s390 __TYPE_IS_PTR macro is pretty weird ;)): --------------------------8<--------------------------------- diff --git a/arch/s390/include/asm/compat.h b/arch/s390/include/asm/compat.h index 63b46e30b2c3..338455a74eff 100644 --- a/arch/s390/include/asm/compat.h +++ b/arch/s390/include/asm/compat.h @@ -11,9 +11,6 @@ #include -#define __TYPE_IS_PTR(t) (!__builtin_types_compatible_p( \ - typeof(0?(__force t)0:0ULL), u64)) - #define __SC_DELOUSE(t,v) ({ \ BUILD_BUG_ON(sizeof(t) > 4 && !__TYPE_IS_PTR(t)); \ (__force t)(__TYPE_IS_PTR(t) ? ((v) & 0x7fffffff) : (v)); \ diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index e2870fe1be5b..b1b9fe8502da 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -119,8 +119,15 @@ struct io_uring_params; #define __TYPE_IS_L(t) (__TYPE_AS(t, 0L)) #define __TYPE_IS_UL(t) (__TYPE_AS(t, 0UL)) #define __TYPE_IS_LL(t) (__TYPE_AS(t, 0LL) || __TYPE_AS(t, 0ULL)) +#define __TYPE_IS_PTR(t) (!__builtin_types_compatible_p(typeof(0 ? (__force t)0 : 0ULL), u64)) #define __SC_LONG(t, a) __typeof(__builtin_choose_expr(__TYPE_IS_LL(t), 0LL, 0L)) a +#ifdef CONFIG_64BIT +#define __SC_CAST(t, a) (__TYPE_IS_PTR(t) \ + ? (__force t) ((__u64)a & ~(1UL << 55)) \ + : (__force t) a) +#else #define __SC_CAST(t, a) (__force t) a +#endif #define __SC_ARGS(t, a) a #define __SC_TEST(t, a) (void)BUILD_BUG_ON_ZERO(!__TYPE_IS_LL(t) && sizeof(t) > sizeof(long)) -- Catalin