From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08558C2D0C6 for ; Fri, 27 Dec 2019 14:34:41 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AE72A20882 for ; Fri, 27 Dec 2019 14:34:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AE72A20882 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4FACB8E0005; Fri, 27 Dec 2019 09:34:40 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4AB1A8E0001; Fri, 27 Dec 2019 09:34:40 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3C2168E0005; Fri, 27 Dec 2019 09:34:40 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0196.hostedemail.com [216.40.44.196]) by kanga.kvack.org (Postfix) with ESMTP id 25FD48E0001 for ; Fri, 27 Dec 2019 09:34:40 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id B89B9181AEF0B for ; Fri, 27 Dec 2019 14:34:39 +0000 (UTC) X-FDA: 76311167478.28.cup57_289a05a532250 X-HE-Tag: cup57_289a05a532250 X-Filterd-Recvd-Size: 9032 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Fri, 27 Dec 2019 14:34:38 +0000 (UTC) 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 E33431FB; Fri, 27 Dec 2019 06:34:37 -0800 (PST) Received: from [10.1.195.17] (e123572-lin.cambridge.arm.com [10.1.195.17]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 96FCB3F68F; Fri, 27 Dec 2019 06:34:36 -0800 (PST) Subject: Re: [PATCH 19/22] arm64: mte: Allow user control of the tag check mode via prctl() To: Catalin Marinas , linux-arm-kernel@lists.infradead.org Cc: Will Deacon , Marc Zyngier , Vincenzo Frascino , Szabolcs Nagy , Richard Earnshaw , Andrey Konovalov , linux-mm@kvack.org, linux-arch@vger.kernel.org References: <20191211184027.20130-1-catalin.marinas@arm.com> <20191211184027.20130-20-catalin.marinas@arm.com> From: Kevin Brodsky Message-ID: Date: Fri, 27 Dec 2019 14:34:32 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20191211184027.20130-20-catalin.marinas@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-GB 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: Not just related to this patch, but here goes. While trying to debug an MTE-enabled process, I realised that there's no way to tell the tagged addr / MTE thread configuration from outside of the thread. At this point I thought it'd be really nice if this were to be exposed in /proc/pid, maybe in /proc/pid/status. Unfortunately there seems to be no precedent for an arch-specific feature to be exposed there. I guess a ptrace call would work as well, although it wouldn't be as practical without using a debugger. Any thoughts? Kevin On 11/12/2019 18:40, 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 > --- > arch/arm64/include/asm/processor.h | 3 + > arch/arm64/kernel/process.c | 119 +++++++++++++++++++++++++++-- > include/uapi/linux/prctl.h | 6 ++ > 3 files changed, 123 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 5ba63204d078..91aa270afc7d 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -148,6 +148,9 @@ struct thread_struct { > #ifdef CONFIG_ARM64_PTR_AUTH > struct ptrauth_keys keys_user; > #endif > +#ifdef CONFIG_ARM64_MTE > + u64 sctlr_tcf0; > +#endif > }; > > static inline void arch_thread_struct_whitelist(unsigned long *offset, > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index dd98d539894e..47ce98f47253 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -317,11 +317,22 @@ static void flush_tagged_addr_state(void) > clear_thread_flag(TIF_TAGGED_ADDR); > } > > +#ifdef CONFIG_ARM64_MTE > +static void flush_mte_state(void) > +{ > + if (!system_supports_mte()) > + return; > + > + /* clear any pending asynchronous tag fault */ > + clear_thread_flag(TIF_MTE_ASYNC_FAULT); > + /* disable tag checking */ > + current->thread.sctlr_tcf0 = 0; > +} > +#else > static void flush_mte_state(void) > { > - if (system_supports_mte()) > - clear_thread_flag(TIF_MTE_ASYNC_FAULT); > } > +#endif > > void flush_thread(void) > { > @@ -484,6 +495,29 @@ static void ssbs_thread_switch(struct task_struct *next) > set_ssbs_bit(regs); > } > > +#ifdef CONFIG_ARM64_MTE > +static void update_sctlr_el1_tcf0(u64 tcf0) > +{ > + /* no need for ISB since this only affects EL0, implicit with ERET */ > + sysreg_clear_set(sctlr_el1, SCTLR_EL1_TCF0_MASK, tcf0); > +} > + > +/* Handle MTE thread switch */ > +static void mte_thread_switch(struct task_struct *next) > +{ > + if (!system_supports_mte()) > + return; > + > + /* avoid expensive SCTLR_EL1 accesses if no change */ > + if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0) > + update_sctlr_el1_tcf0(next->thread.sctlr_tcf0); > +} > +#else > +static void mte_thread_switch(struct task_struct *next) > +{ > +} > +#endif > + > /* > * We store our current task in sp_el0, which is clobbered by userspace. Keep a > * shadow copy so that we can restore this upon entry from userspace. > @@ -514,6 +548,7 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, > uao_thread_switch(next); > ptrauth_thread_switch(next); > ssbs_thread_switch(next); > + mte_thread_switch(next); > > /* > * Complete any pending TLB or cache maintenance on this CPU in case > @@ -574,6 +609,67 @@ void arch_setup_new_exec(void) > ptrauth_thread_init_user(current); > } > > +#ifdef CONFIG_ARM64_MTE > +static long set_mte_ctrl(unsigned long arg) > +{ > + u64 tcf0; > + > + if (!system_supports_mte()) > + return 0; > + > + switch (arg & PR_MTE_TCF_MASK) { > + case PR_MTE_TCF_NONE: > + tcf0 = 0; > + break; > + case PR_MTE_TCF_SYNC: > + tcf0 = SCTLR_EL1_TCF0_SYNC; > + break; > + case PR_MTE_TCF_ASYNC: > + tcf0 = SCTLR_EL1_TCF0_ASYNC; > + break; > + default: > + return -EINVAL; > + } > + > + /* > + * mte_thread_switch() checks current->thread.sctlr_tcf0 as an > + * optimisation. Disable preemption so that it does not see > + * the variable update before the SCTLR_EL1.TCF0 one. > + */ > + preempt_disable(); > + current->thread.sctlr_tcf0 = tcf0; > + update_sctlr_el1_tcf0(tcf0); > + preempt_enable(); > + > + return 0; > +} > + > +static long get_mte_ctrl(void) > +{ > + if (!system_supports_mte()) > + return 0; > + > + switch (current->thread.sctlr_tcf0) { > + case SCTLR_EL1_TCF0_SYNC: > + return PR_MTE_TCF_SYNC; > + case SCTLR_EL1_TCF0_ASYNC: > + return PR_MTE_TCF_ASYNC; > + } > + > + return 0; > +} > +#else > +static long set_mte_ctrl(unsigned long arg) > +{ > + return 0; > +} > + > +static long get_mte_ctrl(void) > +{ > + return 0; > +} > +#endif > + > #ifdef CONFIG_ARM64_TAGGED_ADDR_ABI > /* > * Control the relaxed ABI allowing tagged user addresses into the kernel. > @@ -582,9 +678,15 @@ static unsigned int tagged_addr_disabled; > > long set_tagged_addr_ctrl(unsigned long arg) > { > + unsigned long valid_mask = PR_TAGGED_ADDR_ENABLE; > + > if (is_compat_task()) > return -EINVAL; > - if (arg & ~PR_TAGGED_ADDR_ENABLE) > + > + if (system_supports_mte()) > + valid_mask |= PR_MTE_TCF_MASK; > + > + if (arg & ~valid_mask) > return -EINVAL; > > /* > @@ -594,6 +696,9 @@ long set_tagged_addr_ctrl(unsigned long arg) > if (arg & PR_TAGGED_ADDR_ENABLE && tagged_addr_disabled) > return -EINVAL; > > + if (set_mte_ctrl(arg) != 0) > + return -EINVAL; > + > update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE); > > return 0; > @@ -601,13 +706,17 @@ long set_tagged_addr_ctrl(unsigned long arg) > > long get_tagged_addr_ctrl(void) > { > + long ret = 0; > + > if (is_compat_task()) > return -EINVAL; > > if (test_thread_flag(TIF_TAGGED_ADDR)) > - return PR_TAGGED_ADDR_ENABLE; > + ret = PR_TAGGED_ADDR_ENABLE; > > - return 0; > + ret |= get_mte_ctrl(); > + > + return ret; > } > > /* > diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h > index 7da1b37b27aa..5e9323e66a38 100644 > --- a/include/uapi/linux/prctl.h > +++ b/include/uapi/linux/prctl.h > @@ -233,5 +233,11 @@ struct prctl_mm_map { > #define PR_SET_TAGGED_ADDR_CTRL 55 > #define PR_GET_TAGGED_ADDR_CTRL 56 > # define PR_TAGGED_ADDR_ENABLE (1UL << 0) > +/* MTE tag check fault modes */ > +# define PR_MTE_TCF_SHIFT 1 > +# define PR_MTE_TCF_NONE (0UL << PR_MTE_TCF_SHIFT) > +# define PR_MTE_TCF_SYNC (1UL << PR_MTE_TCF_SHIFT) > +# define PR_MTE_TCF_ASYNC (2UL << PR_MTE_TCF_SHIFT) > +# define PR_MTE_TCF_MASK (3UL << PR_MTE_TCF_SHIFT) > > #endif /* _LINUX_PRCTL_H */