From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH v4 15/26] arm64: mte: Allow user control of the tag check mode via prctl() Date: Wed, 27 May 2020 12:16:31 +0100 Message-ID: <20200527111631.GC28101@gaia> References: <20200515171612.1020-1-catalin.marinas@arm.com> <20200515171612.1020-16-catalin.marinas@arm.com> <20200527074658.GB9887@willie-the-truck> <20200527083218.GS5031@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from foss.arm.com ([217.140.110.172]:36198 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387397AbgE0LQf (ORCPT ); Wed, 27 May 2020 07:16:35 -0400 Content-Disposition: inline In-Reply-To: <20200527083218.GS5031@arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Dave Martin Cc: Will Deacon , linux-arch@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , linux-mm@kvack.org, Vincenzo Frascino , Peter Collingbourne , linux-arm-kernel@lists.infradead.org On Wed, May 27, 2020 at 09:32:20AM +0100, Dave P Martin wrote: > On Wed, May 27, 2020 at 08:46:59AM +0100, Will Deacon wrote: > > On Fri, May 15, 2020 at 06:16:01PM +0100, Catalin Marinas wrote: > > > By default, even if PROT_MTE is set on a memory range, there is no tag > > > check fault reporting (SIGSEGV). Introduce a set of option to the > > > exiting prctl(PR_SET_TAGGED_ADDR_CTRL) to allow user control of the tag > > > check fault mode: > > > > > > PR_MTE_TCF_NONE - no reporting (default) > > > PR_MTE_TCF_SYNC - synchronous tag check fault reporting > > > PR_MTE_TCF_ASYNC - asynchronous tag check fault reporting > > > > > > These options translate into the corresponding SCTLR_EL1.TCF0 bitfield, > > > context-switched by the kernel. Note that uaccess done by the kernel is > > > not checked and cannot be configured by the user. > > > > > > Signed-off-by: Catalin Marinas > > > Cc: Will Deacon > > > --- > > > > > > Notes: > > > v3: > > > - Use SCTLR_EL1_TCF0_NONE instead of 0 for consistency. > > > - Move mte_thread_switch() in this patch from an earlier one. In > > > addition, it is called after the dsb() in __switch_to() so that any > > > asynchronous tag check faults have been registered in the TFSR_EL1 > > > registers (to be added with the in-kernel MTE support. > > > > > > v2: > > > - Handle SCTLR_EL1_TCF0_NONE explicitly for consistency with PR_MTE_TCF_NONE. > > > - Fix SCTLR_EL1 register setting in flush_mte_state() (thanks to Peter > > > Collingbourne). > > > - Added ISB to update_sctlr_el1_tcf0() since, with the latest > > > architecture update/fix, the TCF0 field is used by the uaccess > > > routines. > > > > > > arch/arm64/include/asm/mte.h | 14 ++++++ > > > arch/arm64/include/asm/processor.h | 3 ++ > > > arch/arm64/kernel/mte.c | 77 ++++++++++++++++++++++++++++++ > > > arch/arm64/kernel/process.c | 26 ++++++++-- > > > include/uapi/linux/prctl.h | 6 +++ > > > 5 files changed, 123 insertions(+), 3 deletions(-) > > > > Dave is working on man pages for prctl() (and I think also ptrace). I think > > it would be /very/ useful for us to have some RFC patches on top of his work > > adding documentation for the MTE interactions, as we found some other minor > > issues/inconsistencies as a direct result of writing and reviewing the man > > page for our existing interfaces. > > I have a local draft for the address tagging and MTE prctls already btw. > I hadn't posted them yet so as to focus on nailing the "easy" stuff down > ;) That's great Dave. Thanks! > If I have time I'll try and get them posted today so that people can > take a look before next week. Feel free to post them whenever you can. I'll include them in v5 (likely to be posted after the merging window). -- Catalin