From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3DE9425A2BB; Mon, 25 Aug 2025 03:34:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756092880; cv=none; b=Xo+ZT1gOLEbIdn23Q1nc2INEuClb5xKb7QrnyI/509ku2CFPMoJF4V9+fQt1dEDPnRbe6qgp1cuIYS3FS75NvvBcY4isTRPRR21sKidd9AaS827FJxzUTXt8e24Wjr7I3p39O9HVG1kooCqPmJPlZRFGMwbiCXpzsKCGAANTMHM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756092880; c=relaxed/simple; bh=Z+1IquETUuvnvgb9eqz1cuwQMXLohgMxMNidxvFnrZ0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MyVseF3VQzmI/LFs7pLsCpZpM+COU/oDmrCBdE4HhxeiJGRHaX/oeZndWveP2GsLrwxh4kB5nu2hfnhwxClX1SbNDRqTNrBJPePOWI7SVmUO1caRtD29hhyHeAryudraPFYKZXxbXuycpMHA3YkQlZDFv7zqzuIScmqbZ0DM2H0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 3000915A1; Sun, 24 Aug 2025 20:34:30 -0700 (PDT) Received: from u200865.usa.arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 463933F63F; Sun, 24 Aug 2025 20:34:37 -0700 (PDT) From: Jeremy Linton To: linux-trace-kernel@vger.kernel.org Cc: linux-perf-users@vger.kernel.org, mhiramat@kernel.org, oleg@redhat.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, thiago.bauermann@linaro.org, broonie@kernel.org, yury.khrustalev@arm.com, kristina.martsenko@arm.com, liaochang1@huawei.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Jeremy Linton , Steve Capper Subject: [PATCH v7 5/7] arm64: uprobes: Add GCS support to uretprobes Date: Sun, 24 Aug 2025 22:34:19 -0500 Message-ID: <20250825033421.463669-6-jeremy.linton@arm.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250825033421.463669-1-jeremy.linton@arm.com> References: <20250825033421.463669-1-jeremy.linton@arm.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Ret probes work by changing the value in the link register at the probe location to return to the probe rather than the calling routine. Thus the GCS needs to be updated with this address as well. Since its possible to insert probes at locations where the current value of the LR doesn't match the GCS state this needs to be detected and handled in order to maintain the existing no-fault behavior. Co-developed-by: Steve Capper Signed-off-by: Steve Capper (updated to use new gcs accessors, and handle LR/GCS mismatches) Signed-off-by: Jeremy Linton Reviewed-by: Catalin Marinas --- arch/arm64/kernel/probes/uprobes.c | 33 ++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/arch/arm64/kernel/probes/uprobes.c b/arch/arm64/kernel/probes/uprobes.c index 1f91fd2a8187..6b98503a0198 100644 --- a/arch/arm64/kernel/probes/uprobes.c +++ b/arch/arm64/kernel/probes/uprobes.c @@ -6,6 +6,7 @@ #include #include #include +#include #include "decode-insn.h" @@ -159,11 +160,43 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs) { unsigned long orig_ret_vaddr; + unsigned long gcs_ret_vaddr; + int err = 0; + u64 gcspr; orig_ret_vaddr = procedure_link_pointer(regs); + + if (task_gcs_el0_enabled(current)) { + gcspr = read_sysreg_s(SYS_GCSPR_EL0); + gcs_ret_vaddr = get_user_gcs((unsigned long __user *)gcspr, &err); + if (err) { + force_sig(SIGSEGV); + goto out; + } + + /* + * If the LR and GCS return addr don't match, then some kind of PAC + * signing or control flow occurred since entering the probed function. + * Likely because the user is attempting to retprobe on an instruction + * that isn't a function boundary or inside a leaf function. Explicitly + * abort this retprobe because it will generate a GCS exception. + */ + if (gcs_ret_vaddr != orig_ret_vaddr) { + orig_ret_vaddr = -1; + goto out; + } + + put_user_gcs(trampoline_vaddr, (unsigned long __user *)gcspr, &err); + if (err) { + force_sig(SIGSEGV); + goto out; + } + } + /* Replace the return addr with trampoline addr */ procedure_link_pointer_set(regs, trampoline_vaddr); +out: return orig_ret_vaddr; } -- 2.50.1