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[173.164.112.133]) by smtp.gmail.com with ESMTPSA id x7sm11154611pfm.82.2019.06.10.11.07.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 10 Jun 2019 11:07:04 -0700 (PDT) Date: Mon, 10 Jun 2019 11:07:03 -0700 From: Kees Cook To: Catalin Marinas 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, 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: <201906101106.3CA50745E3@keescook> References: <4327b260fb17c4776a1e3c844f388e4948cfb747.1559580831.git.andreyknvl@google.com> <20190610175326.GC25803@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190610175326.GC25803@arrakis.emea.arm.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Jun 10, 2019 at 06:53:27PM +0100, Catalin Marinas wrote: > On Mon, Jun 03, 2019 at 06:55:04PM +0200, Andrey Konovalov wrote: > > 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) > > I'm going to propose an opt-in method here (RFC for now). We can't have > a check in untagged_addr() since this is already used throughout the > kernel for both user and kernel addresses (khwasan) but we can add one > in __range_ok(). The same prctl() option will be used for controlling > the precise/imprecise mode of MTE later on. We can use a TIF_ flag here > assuming that this will be called early on and any cloned thread will > inherit this. > > Anyway, it's easier to paste some diff than explain but Vincenzo can > fold them into his ABI patches that should really go together with > these. I added a couple of MTE definitions for prctl() as an example, > not used currently: > > ------------------8<--------------------------------------------- > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index fcd0e691b1ea..2d4cb7e4edab 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -307,6 +307,10 @@ extern void __init minsigstksz_setup(void); > /* PR_PAC_RESET_KEYS prctl */ > #define PAC_RESET_KEYS(tsk, arg) ptrauth_prctl_reset_keys(tsk, arg) > > +/* PR_UNTAGGED_UADDR prctl */ > +int untagged_uaddr_set_mode(unsigned long arg); > +#define SET_UNTAGGED_UADDR_MODE(arg) untagged_uaddr_set_mode(arg) > + > /* > * For CONFIG_GCC_PLUGIN_STACKLEAK > * > diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h > index c285d1ce7186..89ce77773c49 100644 > --- a/arch/arm64/include/asm/thread_info.h > +++ b/arch/arm64/include/asm/thread_info.h > @@ -101,6 +101,7 @@ void arch_release_task_struct(struct task_struct *tsk); > #define TIF_SVE 23 /* Scalable Vector Extension in use */ > #define TIF_SVE_VL_INHERIT 24 /* Inherit sve_vl_onexec across exec */ > #define TIF_SSBD 25 /* Wants SSB mitigation */ > +#define TIF_UNTAGGED_UADDR 26 > > #define _TIF_SIGPENDING (1 << TIF_SIGPENDING) > #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) > @@ -116,6 +117,7 @@ void arch_release_task_struct(struct task_struct *tsk); > #define _TIF_FSCHECK (1 << TIF_FSCHECK) > #define _TIF_32BIT (1 << TIF_32BIT) > #define _TIF_SVE (1 << TIF_SVE) > +#define _TIF_UNTAGGED_UADDR (1 << TIF_UNTAGGED_UADDR) > > #define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \ > _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \ > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > index 9164ecb5feca..54f5bbaebbc4 100644 > --- a/arch/arm64/include/asm/uaccess.h > +++ b/arch/arm64/include/asm/uaccess.h > @@ -73,6 +73,9 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si > { > unsigned long ret, limit = current_thread_info()->addr_limit; > > + if (test_thread_flag(TIF_UNTAGGED_UADDR)) > + addr = untagged_addr(addr); > + > __chk_user_ptr(addr); > asm volatile( > // A + B <= C + 1 for all A,B,C, in four easy steps: > @@ -94,7 +97,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si > return ret; > } > > -#define access_ok(addr, size) __range_ok(untagged_addr(addr), size) > +#define access_ok(addr, size) __range_ok(addr, size) > #define user_addr_max get_fs > > #define _ASM_EXTABLE(from, to) \ > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index 3767fb21a5b8..fd191c5b92aa 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -552,3 +552,18 @@ void arch_setup_new_exec(void) > > ptrauth_thread_init_user(current); > } > + > +/* > + * Enable the relaxed ABI allowing tagged user addresses into the kernel. > + */ > +int untagged_uaddr_set_mode(unsigned long arg) > +{ > + if (is_compat_task()) > + return -ENOTSUPP; > + if (arg) > + return -EINVAL; > + > + set_thread_flag(TIF_UNTAGGED_UADDR); > + > + return 0; > +} I think this should be paired with a flag clearing in copy_thread(), yes? (i.e. each binary needs to opt in) -- Kees Cook