From patchwork Mon Oct 9 12:08:58 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13413639 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 84BADE95A9D for ; Mon, 9 Oct 2023 12:16:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346526AbjJIMQN (ORCPT ); Mon, 9 Oct 2023 08:16:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44320 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346459AbjJIMPV (ORCPT ); Mon, 9 Oct 2023 08:15:21 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C8081FCE; Mon, 9 Oct 2023 05:13:27 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93E3DC4167D; Mon, 9 Oct 2023 12:13:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1696853606; bh=ZneLmCePUg63/qsSwQjRgo0lJ2wvCQfwcnIhBN+HCvU=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=pMylGXyro5zpDCWMajUKC7BW/REgEuYKhID+LyYyH5Snn88sviH2mVDG1LqC8DhHu /rb3/WdsVXascc+TWcbAaQm0weKwc4RHZ70ncA8M5m74+GC0jm2FIhgPg6BqEGj35q kuTxVoxUHtlFJ9QB3Dl73QTk+6rSJuXH0kFYYc1iRpFuROKh1KF02HhMwvl/Nb/E8r 3FtkRwb0ogEexxNWpKAKd91RoNh4ExK9KLLNAqVDE7Va4WbOOIh3BJPaA2pvYJ7dwB KE7Jq+y1W0t2C49fls2u2nbbaiXVCOSlnCMtM5nhqTolwzAwx73/nnnUgm1BR+raFh aeDk1sl/8cbfg== From: Mark Brown Date: Mon, 09 Oct 2023 13:08:58 +0100 Subject: [PATCH v6 24/38] arm64/signal: Set up and restore the GCS context for signal handlers MIME-Version: 1.0 Message-Id: <20231009-arm64-gcs-v6-24-78e55deaa4dd@kernel.org> References: <20231009-arm64-gcs-v6-0-78e55deaa4dd@kernel.org> In-Reply-To: <20231009-arm64-gcs-v6-0-78e55deaa4dd@kernel.org> To: Catalin Marinas , Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Kees Cook , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy Cc: "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , 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, Mark Brown X-Mailer: b4 0.13-dev-0438c X-Developer-Signature: v=1; a=openpgp-sha256; l=7272; i=broonie@kernel.org; h=from:subject:message-id; bh=ZneLmCePUg63/qsSwQjRgo0lJ2wvCQfwcnIhBN+HCvU=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBlI+2k+Yu5E/WU+7sfmQCBl2rh45oRS4s0qpeS50/J 6wxbOqSJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZSPtpAAKCRAk1otyXVSH0BTJB/ 9XHnWgdli5cKd6AxjFaDID/jh9Wyh5sSGi9fWVij/UGcOE2B6pBw3mi/DxCe01u2p6yJx5TUMuwbxP aeqLutwc9FpixTiJHU6JDxzlMDYSbhphgMNiY7AY4jBfimBy56c1aLQuKs8dH+EtFNFdKlRPLHNedN nmk51x/P4LGZ/rQrEWMDAMeglVnR2GZFmCmKGAFN71Y6lWJjl/kRrurQwp0tl3KmUyZq2ByedwGTm6 ZmKQCncBQ7OnyZa35wzxpKByWTj6Ponkov5hEtG6aOL9Ksc7j048tu+35DruNM7tJ13846OK+RUJcy DXJ23fGcRtQVlyTpYlktLHU8KcpVIW X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org When invoking a signal handler we use the GCS configuration and stack for the current thread. Since we implement signal return by calling the signal handler with a return address set up pointing to a trampoline in the vDSO we need to also configure any active GCS for this by pushing a frame for the trampoline onto the GCS. If we do not do this then signal return will generate a GCS protection fault. In order to guard against attempts to bypass GCS protections via signal return we only allow returning with GCSPR_EL0 pointing to an address where it was previously preempted by a signal. We do this by pushing a cap onto the GCS, this takes the form of an architectural GCS cap token with the top bit set which we add on signal entry and validate and pop off on signal return. Since the top bit is set address validation for the token will fail if an attempt is made to use it with the stack switch instructions. Signed-off-by: Mark Brown --- arch/arm64/include/asm/gcs.h | 2 + arch/arm64/kernel/signal.c | 130 +++++++++++++++++++++++++++++++++++++++++-- arch/arm64/mm/gcs.c | 1 + 3 files changed, 128 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h index c150e76869a1..65496103d462 100644 --- a/arch/arm64/include/asm/gcs.h +++ b/arch/arm64/include/asm/gcs.h @@ -8,6 +8,8 @@ #include #include +struct ksignal; + static inline void gcsb_dsync(void) { asm volatile(".inst 0xd503227f" : : : "memory"); diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 0e8beb3349ea..97004c52aea3 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include #include @@ -34,6 +35,36 @@ #include #include +#ifdef CONFIG_ARM64_GCS +/* Extra bit set in the address distinguishing a signal cap token. */ +#define GCS_SIGNAL_CAP_FLAG BIT(63) + +#define GCS_SIGNAL_CAP(addr) (GCS_CAP(addr) | GCS_SIGNAL_CAP_FLAG) + +static bool gcs_signal_cap_valid(u64 addr, u64 val) +{ + /* + * The top bit should be set, this is an invalid address for + * EL0 and will only be set for caps created by signals. + */ + if (!(val & GCS_SIGNAL_CAP_FLAG)) + return false; + + /* The rest should be a standard architectural cap token. */ + val &= ~GCS_SIGNAL_CAP_FLAG; + + /* The cap must have the low bits set to a token value */ + if (GCS_CAP_TOKEN(val) != GCS_CAP_VALID_TOKEN) + return false; + + /* The cap must store the VA the cap was stored at */ + if (GCS_CAP_ADDR(addr) != GCS_CAP_ADDR(val)) + return false; + + return true; +} +#endif + /* * Do a signal return; undo the signal stack. These are aligned to 128-bit. */ @@ -815,6 +846,45 @@ static int restore_sigframe(struct pt_regs *regs, return err; } +#ifdef CONFIG_ARM64_GCS +static int gcs_restore_signal(void) +{ + u64 gcspr_el0, cap; + int ret; + + if (!system_supports_gcs()) + return 0; + + if (!(current->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE)) + return 0; + + gcspr_el0 = read_sysreg_s(SYS_GCSPR_EL0); + + /* + * GCSPR_EL0 should be pointing at a capped GCS, read the cap... + */ + gcsb_dsync(); + ret = copy_from_user(&cap, (__user void*)gcspr_el0, sizeof(cap)); + if (ret) + return -EFAULT; + + /* + * ...then check that the cap is the actual GCS before + * restoring it. + */ + if (!gcs_signal_cap_valid(gcspr_el0, cap)) + return -EINVAL; + + current->thread.gcspr_el0 = gcspr_el0 + sizeof(cap); + write_sysreg_s(current->thread.gcspr_el0, SYS_GCSPR_EL0); + + return 0; +} + +#else +static int gcs_restore_signal(void) { return 0; } +#endif + SYSCALL_DEFINE0(rt_sigreturn) { struct pt_regs *regs = current_pt_regs(); @@ -841,6 +911,9 @@ SYSCALL_DEFINE0(rt_sigreturn) if (restore_altstack(&frame->uc.uc_stack)) goto badframe; + if (gcs_restore_signal()) + goto badframe; + return regs->regs[0]; badframe: @@ -1071,7 +1144,52 @@ static int get_sigframe(struct rt_sigframe_user_layout *user, return 0; } -static void setup_return(struct pt_regs *regs, struct k_sigaction *ka, +#ifdef CONFIG_ARM64_GCS + +static int gcs_signal_entry(__sigrestore_t sigtramp, struct ksignal *ksig) +{ + unsigned long __user *gcspr_el0; + unsigned long cap[2]; + int ret; + + if (!system_supports_gcs()) + return 0; + + if (!task_gcs_el0_enabled(current)) + return 0; + + /* + * We are entering a signal handler, current register state is + * active. + */ + gcspr_el0 = (unsigned long __user *)read_sysreg_s(SYS_GCSPR_EL0); + + /* + * Push a cap and the GCS entry for the trampoline onto the GCS. + */ + cap[1] = GCS_SIGNAL_CAP(gcspr_el0 - 1); + cap[0] = (unsigned long)sigtramp; + ret = copy_to_user_gcs(gcspr_el0 - 2, cap, ARRAY_SIZE(cap)); + if (ret != 0) + return ret; + + gcsb_dsync(); + + gcspr_el0 -= 2; + write_sysreg_s((unsigned long)gcspr_el0, SYS_GCSPR_EL0); + + return 0; +} +#else + +static int gcs_signal_entry(__sigrestore_t sigtramp, struct ksignal *ksig) +{ + return 0; +} + +#endif + +static int setup_return(struct pt_regs *regs, struct ksignal *ksig, struct rt_sigframe_user_layout *user, int usig) { __sigrestore_t sigtramp; @@ -1079,7 +1197,7 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka, regs->regs[0] = usig; regs->sp = (unsigned long)user->sigframe; regs->regs[29] = (unsigned long)&user->next_frame->fp; - regs->pc = (unsigned long)ka->sa.sa_handler; + regs->pc = (unsigned long)ksig->ka.sa.sa_handler; /* * Signal delivery is a (wacky) indirect function call in @@ -1119,12 +1237,14 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka, sme_smstop(); } - if (ka->sa.sa_flags & SA_RESTORER) - sigtramp = ka->sa.sa_restorer; + if (ksig->ka.sa.sa_flags & SA_RESTORER) + sigtramp = ksig->ka.sa.sa_restorer; else sigtramp = VDSO_SYMBOL(current->mm->context.vdso, sigtramp); regs->regs[30] = (unsigned long)sigtramp; + + return gcs_signal_entry(sigtramp, ksig); } static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set, @@ -1147,7 +1267,7 @@ static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set, err |= __save_altstack(&frame->uc.uc_stack, regs->sp); err |= setup_sigframe(&user, regs, set); if (err == 0) { - setup_return(regs, &ksig->ka, &user, usig); + err = setup_return(regs, ksig, &user, usig); if (ksig->ka.sa.sa_flags & SA_SIGINFO) { err |= copy_siginfo_to_user(&frame->info, &ksig->info); regs->regs[1] = (unsigned long)&frame->info; diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c index c718ac4325bb..32e22bff9bce 100644 --- a/arch/arm64/mm/gcs.c +++ b/arch/arm64/mm/gcs.c @@ -6,6 +6,7 @@ #include #include +#include #include static unsigned long alloc_gcs(unsigned long addr, unsigned long size,