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Thu, 28 Sep 2023 00:41:01 GMT Received: from [10.239.133.73] (10.80.80.8) by nasanex01a.na.qualcomm.com (10.52.223.231) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.36; Wed, 27 Sep 2023 17:40:56 -0700 Message-ID: <29bf8f4c-44b8-ab22-aa66-3e3040012ee5@quicinc.com> Date: Thu, 28 Sep 2023 08:40:53 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.15.0 Subject: Re: [PATCH] ARM: kprobes: Explicitly assign register for local variables To: Ard Biesheuvel CC: , , , , , , References: <20230927055954.3755-1-quic_aiquny@quicinc.com> From: "Aiqun(Maria) Yu" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nasanex01a.na.qualcomm.com (10.52.223.231) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: 48pTDNQJmkfH3nNm6CBXIc978Y8EYfIl X-Proofpoint-GUID: 48pTDNQJmkfH3nNm6CBXIc978Y8EYfIl X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-09-27_16,2023-09-27_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 adultscore=0 bulkscore=0 suspectscore=0 mlxscore=0 mlxlogscore=818 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2309180000 definitions=main-2309280003 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/27/2023 6:11 PM, Ard Biesheuvel wrote: > On Wed, 27 Sept 2023 at 09:44, Aiqun(Maria) Yu wrote: >> >> On 9/27/2023 5:26 PM, Ard Biesheuvel wrote: >>> Hello Maria, >>> >>> On Wed, 27 Sept 2023 at 06:00, Maria Yu wrote: >>>> >>>> Registers r7 is removed in clobber list, so compiler may choose r7 for >>>> local variables usage, while r7 will be actually updated by the inline asm >>>> code. >>> >>> The inline asm does not update R7, it preserves and restores it. >> That is the asm is updating r7 purposely and compiler still choose r7 >> for the asm local varialbe and use it inside the asm code. >> So the change is to fix the issue when "r7 is removed from the clobber >> list of current asm code while actually r7 shouldn't be choosed for the >> current asm local variables". >> The issue is only reproducible when ftrace is not enabled, and r7 is >> removed from the current clobber list. >> >> Let me have the assemble code that will make you understand better. >> >> --the original code: >> "mov r11, r7 \n\t" >> ... >> "ldmia %[regs], {r0-r7} \n\t" >> "blx %[fn] \n\t" >> ... >> "mov r7, r11 \n\t" >> >> --After compile to choose register for [fn] and [regs]. >> mov r11, r7 >> ldr  r7, [r1, #16] //r7 used for store asi->insn_fn >> ... >> ldmia.w  ip, {r0, r1, r2, r3, r4, r5, r6, r7} >> blx r7 >> ... >> mov r7,r11 >> >> The current change is to avoid by fix the registers for local variable >> usage and not choose r7 for [fn]. >> > > OK, I understand now, thanks. > > Would it help if we just always enabled frame pointers for this source file? > > --- a/arch/arm/probes/kprobes/Makefile > +++ b/arch/arm/probes/kprobes/Makefile > @@ -9,6 +9,7 @@ test-kprobes-objs := test-core.o > ifdef CONFIG_THUMB2_KERNEL > obj-$(CONFIG_KPROBES) += actions-thumb.o checkers-thumb.o > test-kprobes-objs += test-thumb.o > +KBUILD_CFLAGS += -fno-omit-frame-pointer I've tried this before, but it didn't work. The compiler(clang 17 here I am using) will still complain for "inline asm clobber list contains reserved registers" when ftrace enabled. > else > obj-$(CONFIG_KPROBES) += actions-arm.o checkers-arm.o > obj-$(CONFIG_OPTPROBES) += opt-arm.o -- Thx and BRs, Aiqun(Maria) Yu