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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 60099C3DA4A for ; Mon, 19 Aug 2024 12:04:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E15736B007B; Mon, 19 Aug 2024 08:04:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DC5B06B0082; Mon, 19 Aug 2024 08:04:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C8E3C6B0083; Mon, 19 Aug 2024 08:04:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id A62A86B007B for ; Mon, 19 Aug 2024 08:04:29 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 3B5601A12B0 for ; Mon, 19 Aug 2024 12:04:29 +0000 (UTC) X-FDA: 82468862658.06.6725929 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf24.hostedemail.com (Postfix) with ESMTP id 65B72180027 for ; Mon, 19 Aug 2024 12:04:27 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=none; spf=pass (imf24.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1724069006; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Tr/q31VjgkKVA4D2EJ6Z/sqW8rrxYeaXvY3ND/5UWPA=; b=QPYmMUJPfqVF35+qNVDxWgKjdLCj7KsjfR1LrfZ+LaK2lRPNOVG9pbe2jnPt1t5B2NRXdh 8irrM4k9lkzbHk03Wofp9h1cRCANUS3Hi1U6dmMhvSNDQdT81ABamAKCl8SZ5t9eHsT1CD avBntkAxzV2D4ZKTelQjhxo4k+ePIS4= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none; spf=pass (imf24.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1724069006; a=rsa-sha256; cv=none; b=pS0wkqonBIbcz0VN00B+tED/gpyhNNu+ndWgaBupXEAEpokd8fO9lAuwzsALMZbM7h4jr3 k1k/in27F69ilfkG/+yUYNRGevReVlpvQhZsuuDVLmPak5lW8QsdmaxQl03vUc7SXMGBUl THq7iO2aDvx0Rw4qt4+omr9Pt4EJ63M= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 4C93E60DCE; Mon, 19 Aug 2024 12:04:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 949ABC32782; Mon, 19 Aug 2024 12:04:20 +0000 (UTC) Date: Mon, 19 Aug 2024 13:04:18 +0100 From: Catalin Marinas To: Mark Brown Cc: Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , Kees Cook , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , Thiago Jung Bauermann , Ross Burton , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v10 20/40] arm64/gcs: Ensure that new threads have a GCS Message-ID: References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org> <20240801-arm64-gcs-v10-20-699e2bd2190b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240801-arm64-gcs-v10-20-699e2bd2190b@kernel.org> X-Stat-Signature: f4y1zzewi3xyreseu179rhu8ceip31i1 X-Rspam-User: X-Rspamd-Queue-Id: 65B72180027 X-Rspamd-Server: rspam02 X-HE-Tag: 1724069067-641462 X-HE-Meta: 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 qH0MLR0l DbSLuCnGa4DyHZHhNes7dMNkhLziPv3Bga49Q7cO741aYiyaaRwESepeifOV8uGsQZ7berooRP0CE3MhM291mIKoCctVLuHhVzEvSXKX7DAb5z775dUtyUY0HYh7fe5yKbiwPNtGbE5R33MhE5NYvE8K4kq0FMhk2rgFdfXpDOKk2sBOUnoZfbZzIrw9MyoywnQ3rHDVhY8blAt3zZkzI/igDgZDGexCWVQ8phsIeAaN17rW9orfyJPrDsYYsIeRjArJYf4Lz9g3hZp9s7B4jmAHVl3FYXy18K7TZbUmjwKvb6mbbuEMv11LnvYFp/UKaETTys7CaRGfrOIvDLwpRY89t69wDn6rKKeis4eZkwGHyc6IhQmy6o6aBXAh2Am2CKrJm9RlSARY3YH4e/0cOtQ9ZcVWweoPXmDdzoHQtuKDVPkg= 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: List-Subscribe: List-Unsubscribe: On Thu, Aug 01, 2024 at 01:06:47PM +0100, Mark Brown wrote: > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index 5f00cb0da9c3..d6d3a96cf2e4 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -285,9 +285,32 @@ static void flush_gcs(void) > write_sysreg_s(0, SYS_GCSPR_EL0); > } > > +static int copy_thread_gcs(struct task_struct *p, > + const struct kernel_clone_args *args) > +{ > + unsigned long gcs; > + > + gcs = gcs_alloc_thread_stack(p, args); > + if (IS_ERR_VALUE(gcs)) > + return PTR_ERR((void *)gcs); Is 0 an ok value here? I can see further down that gcs_alloc_thread_stack() may return 0. > + > + p->thread.gcs_el0_mode = current->thread.gcs_el0_mode; > + p->thread.gcs_el0_locked = current->thread.gcs_el0_locked; > + > + /* Ensure the current state of the GCS is seen by CoW */ > + gcsb_dsync(); I don't get this barrier. What does it have to do with CoW, which memory effects is it trying to order? > diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c > index b0a67efc522b..b71f6b408513 100644 > --- a/arch/arm64/mm/gcs.c > +++ b/arch/arm64/mm/gcs.c > @@ -8,6 +8,138 @@ > #include > #include > > +static unsigned long alloc_gcs(unsigned long addr, unsigned long size) > +{ > + int flags = MAP_ANONYMOUS | MAP_PRIVATE; > + struct mm_struct *mm = current->mm; > + unsigned long mapped_addr, unused; > + > + if (addr) > + flags |= MAP_FIXED_NOREPLACE; > + > + mmap_write_lock(mm); > + mapped_addr = do_mmap(NULL, addr, size, PROT_READ, flags, > + VM_SHADOW_STACK | VM_WRITE, 0, &unused, NULL); > + mmap_write_unlock(mm); > + > + return mapped_addr; > +} > + > +static unsigned long gcs_size(unsigned long size) > +{ > + if (size) > + return PAGE_ALIGN(size); > + > + /* Allocate RLIMIT_STACK/2 with limits of PAGE_SIZE..2G */ > + size = PAGE_ALIGN(min_t(unsigned long long, > + rlimit(RLIMIT_STACK) / 2, SZ_2G)); > + return max(PAGE_SIZE, size); > +} So we still have RLIMIT_STACK/2. I thought we got rid of that and just went with RLIMIT_STACK (or I misremember). > + > +static bool gcs_consume_token(struct mm_struct *mm, unsigned long user_addr) > +{ > + u64 expected = GCS_CAP(user_addr); > + u64 val; > + int ret; > + > + /* This should really be an atomic cmpxchg. It is not. */ > + ret = access_remote_vm(mm, user_addr, &val, sizeof(val), > + FOLL_FORCE); > + if (ret != sizeof(val)) > + return false; > + > + if (val != expected) > + return false; > + > + val = 0; > + ret = access_remote_vm(mm, user_addr, &val, sizeof(val), > + FOLL_FORCE | FOLL_WRITE); > + if (ret != sizeof(val)) > + return false; > + > + return true; > +} As per the clone3() thread, I think we should try to use get_user_page_vma_remote() and do a cmpxchg() directly. How does the user write the initial token? Do we need any barriers before/after consuming the token? -- Catalin