From patchwork Wed Nov 22 09:42:34 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13464383 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D8B7219F4; Wed, 22 Nov 2023 09:45:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="U4bwvIok" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C8647C433C7; Wed, 22 Nov 2023 09:45:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1700646355; bh=JSMKZVTb8W/3p+ZC0+L/d3j69dhWO4dnKUlZwbrdLaI=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=U4bwvIokG8EBOx6vV6+qI7PoxqEUT6THnfDrDq1mSrjFlRQnyk3mldrsV93A4RKJa Ab8+infWBXCxq3HWoxF+Rgts7qb5Vr9GbzdBdzX/QP4QpKQkQ/2QSTT6x6sIwYWirn BLgVCFQxL/e9dcHNNRJqWIJv1XpTSq+v9BRpNLM63JBxA/EL4GPQZ+FSB1yvjDF/tE jRAhvJCYRVY545coOpYO4b6zCpWJhzoa76at3Ag5n/yOKCf71oXBG5yOJ99685CWe+ jTWgch4JvU7mTRWUWV7ZCIyXqDxDJmYJXJkS661Flns6yYwdYHYwa9X38FpoqqL1K+ j2c9XuOOQDc9Q== From: Mark Brown Date: Wed, 22 Nov 2023 09:42:34 +0000 Subject: [PATCH v7 24/39] arm64/signal: Set up and restore the GCS context for signal handlers Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20231122-arm64-gcs-v7-24-201c483bd775@kernel.org> References: <20231122-arm64-gcs-v7-0-201c483bd775@kernel.org> In-Reply-To: <20231122-arm64-gcs-v7-0-201c483bd775@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 , Thiago Jung Bauermann , 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=7224; i=broonie@kernel.org; h=from:subject:message-id; bh=JSMKZVTb8W/3p+ZC0+L/d3j69dhWO4dnKUlZwbrdLaI=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBlXc0JNdS11sr/Hjge1PGfZqER4xUAoTpU9oiaf FJ+aEPK/b+JATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZV3NCQAKCRAk1otyXVSH 0BhgB/9wTBjvZo5XENLoyEPM8e1KArN74mpxK9+U6onYgUXq7Hkos33gETCBKyt4RZgN1HezEtY KP/9WhVc+tZTxnGd6ycY8s+k7os236QxAWzAgt/ivN+S9uYY0GTGs0l9VE9Nz9kHLzFLIy0SttB w2sViEpIqU8+ewskH7BJA6S4qgEFx4XmvWi/sr1O3Opj6EqosGlFI4l2VkWKqWEvBydESKE9HQB 1pTNOoiYU+pTtqjt/ghPMIK0/A/yUfohxaYdvnuvApLKrxOk2qwBGsNyvzT4aNk/qMgbw5OZ/JV aX1ofsQjx23b5yhe9sX8DOrhH8LfB7WGT1kAxw1at/EmK8q0 X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB 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 and token type of 0 which we add on signal entry and validate and pop off on signal return. The combination of the top bit being set and the token type mean that this can't be interpreted as a valid token or address. Signed-off-by: Mark Brown --- arch/arm64/include/asm/gcs.h | 1 + arch/arm64/kernel/signal.c | 129 +++++++++++++++++++++++++++++++++++++++++-- arch/arm64/mm/gcs.c | 1 + 3 files changed, 126 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h index 48c97e63e56a..f50660603ecf 100644 --- a/arch/arm64/include/asm/gcs.h +++ b/arch/arm64/include/asm/gcs.h @@ -9,6 +9,7 @@ #include struct kernel_clone_args; +struct ksignal; static inline void gcsb_dsync(void) { diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 0e8beb3349ea..b5dff91274fb 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 +35,37 @@ #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) ((((unsigned long)addr) & GCS_CAP_ADDR_MASK) | \ + 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) != 0) + 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 +847,45 @@ 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 +912,9 @@ 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 +1145,50 @@ 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; + int ret = 0; + + 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. + */ + put_user_gcs((unsigned long)sigtramp, gcspr_el0 - 2, &ret); + put_user_gcs(GCS_SIGNAL_CAP(gcspr_el0 - 1), gcspr_el0 - 1, &ret); + 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 +1196,7 @@ 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 +1236,14 @@ 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 +1266,7 @@ 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 02f8f6046c10..6f51429c5a46 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,