From patchwork Mon Nov 29 13:57:09 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 12693904 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F0698C4332F for ; Mon, 29 Nov 2021 13:58:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Message-Id:Date:Subject:Cc :To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References: List-Owner; bh=lxFh1F3IHp3AhIDkUytrG1KFuQavqzRLfSHCX23qcfk=; b=CjAIUVtcnqC4ci tPQFHdazd3NkBE3N8PtdkqeG2TN45Xwl4YUYe9vYw6H4RqdoaYXyIje3pm4HslZsiQHpKKQQsoJ5v +sAQPVcDPQa1usE5N/QcFzC2pUMb6U5QvB872fF4KHBj2KM/EMryqOgReBnPJ/XcGsu061xgzo0Jx maNbdFagVGiXm3Q3NB8PknSIjHvjcanbfkPZI+6Cn4VtC3H2Vj9w9ps64RgUTRK8LWbAUl+ZPR9Xa VCUGplVPDOQJmox/M2yTO/Mq9Lb4lrfY9v2fpgFLNlTzjuymDvtOskrfXXQSrxGCFB/NnkSDqzLQi wAtfdxD+geAHw9UGgtDQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mrh9k-000vRG-2Z; Mon, 29 Nov 2021 13:57:20 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mrh9f-000vQD-O1 for linux-arm-kernel@lists.infradead.org; Mon, 29 Nov 2021 13:57:17 +0000 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 E76831042; Mon, 29 Nov 2021 05:57:14 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 276703F766; Mon, 29 Nov 2021 05:57:14 -0800 (PST) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: broonie@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, will@kernel.org Subject: [PATCH] arm64: ftrace: add missing BTIs Date: Mon, 29 Nov 2021 13:57:09 +0000 Message-Id: <20211129135709.2274019-1-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211129_055715_896725_03985ADB X-CRM114-Status: GOOD ( 10.48 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org When branch target identifiers are in use, code reachable via an indirect branch requires a BTI landing pad at the branch target site. When building FTRACE_WITH_REGS atop patchable-function-entry, we miss BTIs at the start start of the `ftrace_caller` and `ftrace_regs_caller` trampolines, and when these are called from a module via a PLT (which will use a `BR X16`), we will encounter a BTI failure, e.g. | # insmod lkdtm.ko | lkdtm: No crash points registered, enable through debugfs | # echo function_graph > /sys/kernel/debug/tracing/current_tracer | # cat /sys/kernel/debug/provoke-crash/DIRECT | Unhandled 64-bit el1h sync exception on CPU0, ESR 0x34000001 -- BTI | CPU: 0 PID: 174 Comm: cat Not tainted 5.16.0-rc2-dirty #3 | Hardware name: linux,dummy-virt (DT) | pstate: 60400405 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=jc) | pc : ftrace_caller+0x0/0x3c | lr : lkdtm_debugfs_open+0xc/0x20 [lkdtm] | sp : ffff800012e43b00 | x29: ffff800012e43b00 x28: 0000000000000000 x27: ffff800012e43c88 | x26: 0000000000000000 x25: 0000000000000000 x24: ffff0000c171f200 | x23: ffff0000c27b1e00 x22: ffff0000c2265240 x21: ffff0000c23c8c30 | x20: ffff8000090ba380 x19: 0000000000000000 x18: 0000000000000000 | x17: 0000000000000000 x16: ffff80001002bb4c x15: 0000000000000000 | x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000900ff0 | x11: ffff0000c4166310 x10: ffff800012e43b00 x9 : ffff8000104f2384 | x8 : 0000000000000001 x7 : 0000000000000000 x6 : 000000000000003f | x5 : 0000000000000040 x4 : ffff800012e43af0 x3 : 0000000000000001 | x2 : ffff8000090b0000 x1 : ffff0000c171f200 x0 : ffff0000c23c8c30 | Kernel panic - not syncing: Unhandled exception | CPU: 0 PID: 174 Comm: cat Not tainted 5.16.0-rc2-dirty #3 | Hardware name: linux,dummy-virt (DT) | Call trace: | dump_backtrace+0x0/0x1a4 | show_stack+0x24/0x30 | dump_stack_lvl+0x68/0x84 | dump_stack+0x1c/0x38 | panic+0x168/0x360 | arm64_exit_nmi.isra.0+0x0/0x80 | el1h_64_sync_handler+0x68/0xd4 | el1h_64_sync+0x78/0x7c | ftrace_caller+0x0/0x3c | do_dentry_open+0x134/0x3b0 | vfs_open+0x38/0x44 | path_openat+0x89c/0xe40 | do_filp_open+0x8c/0x13c | do_sys_openat2+0xbc/0x174 | __arm64_sys_openat+0x6c/0xbc | invoke_syscall+0x50/0x120 | el0_svc_common.constprop.0+0xdc/0x100 | do_el0_svc+0x84/0xa0 | el0_svc+0x28/0x80 | el0t_64_sync_handler+0xa8/0x130 | el0t_64_sync+0x1a0/0x1a4 | SMP: stopping secondary CPUs | Kernel Offset: disabled | CPU features: 0x0,00000f42,da660c5f | Memory Limit: none | ---[ end Kernel panic - not syncing: Unhandled exception ]--- Fix this by adding the required `BTI C`, as we only require these to be reachable via BL for direct calls or BR X16/X17 for PLTs. For now, these are open-coded in the function prologue, matching the style of the `__hwasan_tag_mismatch` trampoline. In future we may wish to consider adding a new SYM_CODE_START_*() variant which has an implicit BTI. When ftrace is built atop mcount, the trampolines are marked with SYM_FUNC_START(), and so get an implicit BTI. We may need to change these over to SYM_CODE_START() in future for RELIABLE_STACKTRACE, in case we need to apply special care aroud the return address being rewritten. Fixes: 97fed779f2a68937 ("arm64: bti: Provide Kconfig for kernel mode BTI") Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Mark Brown Cc: Will Deacon Reviewed-by: Mark Brown --- arch/arm64/kernel/entry-ftrace.S | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S index b3e4f9a088b1..8cf970d219f5 100644 --- a/arch/arm64/kernel/entry-ftrace.S +++ b/arch/arm64/kernel/entry-ftrace.S @@ -77,11 +77,17 @@ .endm SYM_CODE_START(ftrace_regs_caller) +#ifdef BTI_C + BTI_C +#endif ftrace_regs_entry 1 b ftrace_common SYM_CODE_END(ftrace_regs_caller) SYM_CODE_START(ftrace_caller) +#ifdef BTI_C + BTI_C +#endif ftrace_regs_entry 0 b ftrace_common SYM_CODE_END(ftrace_caller)