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Tue, 18 Nov 2025 17:04:28 GMT Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 731132004D; Tue, 18 Nov 2025 17:04:28 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9933E2004B; Tue, 18 Nov 2025 17:04:27 +0000 (GMT) Received: from [9.155.200.37] (unknown [9.155.200.37]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 18 Nov 2025 17:04:27 +0000 (GMT) Message-ID: Date: Tue, 18 Nov 2025 18:04:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 03/15] unwind_user/sframe: Add support for reading .sframe headers To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, Steven Rostedt , Josh Poimboeuf Cc: Masami Hiramatsu , Mathieu Desnoyers , Peter Zijlstra , Ingo Molnar , Jiri Olsa , Arnaldo Carvalho de Melo , Namhyung Kim , Thomas Gleixner , Andrii Nakryiko , Indu Bhagat , "Jose E. 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Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Heiko Carstens , Vasily Gorbik , "Steven Rostedt (Google)" References: <20251022144326.4082059-1-jremus@linux.ibm.com> <20251022144326.4082059-4-jremus@linux.ibm.com> Content-Language: en-US From: Jens Remus Organization: IBM Deutschland Research & Development GmbH In-Reply-To: <20251022144326.4082059-4-jremus@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: V9xFeZ-ISUTWS4Yz3HEfN4KzcAl4q8It X-Authority-Analysis: v=2.4 cv=Rv3I7SmK c=1 sm=1 tr=0 ts=691ca722 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=5IsC6wTpv4i_iJZREhUA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=DXsff8QfwkrTrK3sU8N1:22 a=Z5ABNNGmrOfJ6cZ5bIyy:22 a=bWyr8ysk75zN3GCy5bjg:22 X-Proofpoint-GUID: 4sK-gnDjYQrV3c78NwXR2VgwKDcxHk0C X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfX00p+GvsXwWsL 99UQLrEJdv/87Bi9UJUR/dzFbyC5q33Ywzwyelr5euiJ6eOjsZPGpV3i863qQ3mvTXK1pTP9omD 88h2NYITEfIluJh0shbkujutN+JXsCUPRAAWQ+ksTE9OM0KocFKUEMfUFDudi98m1GuuXUmgoxC hNruG3iuHIVzjV/Uj6BPjATiIQXU4JaqBU1wDuE7NtGrjTBi6fixDiiUPPdm3GcyJvG6o2SSI/z 0L1X1ejxZNmQI1oT677RzJ1dten6eO5QVp9NwKpQod5wB/k78SQOFbiqOwU8hqb3JL683ezSfmI HIEfiQ/Avvxc3odgSASGXHuox7weRkZXGEdQ/rsZxrXXu02Yi60E23ujRvt2Bcmf9J+jEjTNlSf /jDQJJefA9+M5jmGSO3/yqTPa2ATwA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-18_02,2025-11-18_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 clxscore=1015 phishscore=0 priorityscore=1501 spamscore=0 lowpriorityscore=0 impostorscore=0 adultscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B0318180004 X-Stat-Signature: uediy34qhzexnjk7z6ha46rkth53wh4x X-Rspam-User: X-HE-Tag: 1763485531-833698 X-HE-Meta: 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 QSrt3+3p 8S30FK6KUjNj7sOEMLbIKNyAeJfi2l7jSV0cmZ2TTvbzK+Gj5AzQsHhUnM8AJfW9RFETZfPKK5+agPLme566xNlPlnXYI7CXfTAWwFBGZX0sMjgtWFj/r00ohSSq/vlKJZ3XP/OXI15xxc8p9L1AddX8Cm2D87xFk9vqUdm5Xpmq5p9Qn4Of158Aro0IqTkFnrj4tKcQXvv4Xl3Caxu95I7GTcJ9qAaS2OlvvRxem6BP61fYEaf31FVB7sEO4ISEE3DT+m3z53DvjLqG1Nc0xlXPSMMsMQOhFzv1F7Cv/+eb82q4VNxiFXJvBi2uTCoBFaWfp9LcUBFJjYfRQEQQkJ5zRyyA3+6lBu2S8Rfq9MS6nMF1NSmuC9e3YOY4fBVzgQ32eecFaXmWkxYqCZnFFW59avuX34iACh8Gj X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Josh and Steven! On 10/22/2025 4:43 PM, Jens Remus wrote: > From: Josh Poimboeuf > > In preparation for unwinding user space stacks with sframe, add basic > sframe compile infrastructure and support for reading the .sframe > section header. > > sframe_add_section() reads the header and unconditionally returns an > error, so it's not very useful yet. A subsequent patch will improve > that. > > Link: https://lore.kernel.org/all/f27e8463783febfa0dabb0432a3dd6be8ad98412.1737511963.git.jpoimboe@kernel.org/ > > [ Jens Remus: Add support for PC-relative FDE function start address. ] I took a closer look and wondered whether some parts should better be moved to subsequent patches. > diff --git a/include/linux/sframe.h b/include/linux/sframe.h > @@ -0,0 +1,40 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _LINUX_SFRAME_H > +#define _LINUX_SFRAME_H > + > +#include Move to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data in per-mm maple tree". > +#include Move to "[PATCH v11 06/15] unwind_user/sframe: Add support for reading .sframe contents". find_sframe() needs the types. > + > +#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME > + > +struct sframe_section { > + unsigned long sframe_start; > + unsigned long sframe_end; > + unsigned long text_start; > + unsigned long text_end; > + > + unsigned long fdes_start; > + unsigned long fres_start; > + unsigned long fres_end; > + unsigned int num_fdes; > + > + signed char ra_off; > + signed char fp_off; > +}; > + > +extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end, > + unsigned long text_start, unsigned long text_end); > +extern int sframe_remove_section(unsigned long sframe_addr); > + > +#else /* !CONFIG_HAVE_UNWIND_USER_SFRAME */ > + > +static inline int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end, > + unsigned long text_start, unsigned long text_end) > +{ > + return -ENOSYS; > +} > +static inline int sframe_remove_section(unsigned long sframe_addr) { return -ENOSYS; } > + > +#endif /* CONFIG_HAVE_UNWIND_USER_SFRAME */ > + > +#endif /* _LINUX_SFRAME_H */ > diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c > @@ -0,0 +1,137 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Userspace sframe access functions > + */ > + > +#define pr_fmt(fmt) "sframe: " fmt > + > +#include > +#include > +#include > +#include > +#include Move to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data in per-mm maple tree". > +#include > +#include > +#include > + > +#include "sframe.h" > + > +#define dbg(fmt, ...) \ > + pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__) > + > +static void free_section(struct sframe_section *sec) > +{ > + kfree(sec); > +} > + > +static int sframe_read_header(struct sframe_section *sec) > +{ > + unsigned long header_end, fdes_start, fdes_end, fres_start, fres_end; > + struct sframe_header shdr; > + unsigned int num_fdes; > + > + if (copy_from_user(&shdr, (void __user *)sec->sframe_start, sizeof(shdr))) { > + dbg("header usercopy failed\n"); > + return -EFAULT; > + } > + > + if (shdr.preamble.magic != SFRAME_MAGIC || > + shdr.preamble.version != SFRAME_VERSION_2 || > + !(shdr.preamble.flags & SFRAME_F_FDE_SORTED) || > + !(shdr.preamble.flags & SFRAME_F_FDE_FUNC_START_PCREL) || > + shdr.auxhdr_len) { > + dbg("bad/unsupported sframe header\n"); > + return -EINVAL; > + } > + > + if (!shdr.num_fdes || !shdr.num_fres) { > + dbg("no fde/fre entries\n"); > + return -EINVAL; > + } > + > + header_end = sec->sframe_start + SFRAME_HEADER_SIZE(shdr); > + if (header_end >= sec->sframe_end) { > + dbg("header doesn't fit in section\n"); > + return -EINVAL; > + } > + > + num_fdes = shdr.num_fdes; > + fdes_start = header_end + shdr.fdes_off; > + fdes_end = fdes_start + (num_fdes * sizeof(struct sframe_fde)); > + > + fres_start = header_end + shdr.fres_off; > + fres_end = fres_start + shdr.fre_len; > + > + if (fres_start < fdes_end || fres_end > sec->sframe_end) { > + dbg("inconsistent fde/fre offsets\n"); > + return -EINVAL; > + } > + > + sec->num_fdes = num_fdes; > + sec->fdes_start = fdes_start; > + sec->fres_start = fres_start; > + sec->fres_end = fres_end; > + > + sec->ra_off = shdr.cfa_fixed_ra_offset; > + sec->fp_off = shdr.cfa_fixed_fp_offset; > + > + return 0; > +} > + > +int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end, > + unsigned long text_start, unsigned long text_end) > +{ > + struct maple_tree *sframe_mt = ¤t->mm->sframe_mt; Move to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data in per-mm maple tree". > + struct vm_area_struct *sframe_vma, *text_vma; > + struct mm_struct *mm = current->mm; > + struct sframe_section *sec; > + int ret; > + > + if (!sframe_start || !sframe_end || !text_start || !text_end) { > + dbg("zero-length sframe/text address\n"); > + return -EINVAL; > + } > + > + scoped_guard(mmap_read_lock, mm) { > + sframe_vma = vma_lookup(mm, sframe_start); > + if (!sframe_vma || sframe_end > sframe_vma->vm_end) { > + dbg("bad sframe address (0x%lx - 0x%lx)\n", > + sframe_start, sframe_end); > + return -EINVAL; > + } > + > + text_vma = vma_lookup(mm, text_start); > + if (!text_vma || > + !(text_vma->vm_flags & VM_EXEC) || > + text_end > text_vma->vm_end) { > + dbg("bad text address (0x%lx - 0x%lx)\n", > + text_start, text_end); > + return -EINVAL; > + } > + } > + > + sec = kzalloc(sizeof(*sec), GFP_KERNEL); > + if (!sec) > + return -ENOMEM; > + > + sec->sframe_start = sframe_start; > + sec->sframe_end = sframe_end; > + sec->text_start = text_start; > + sec->text_end = text_end; > + > + ret = sframe_read_header(sec); > + if (ret) > + goto err_free; > + > + /* TODO nowhere to store it yet - just free it and return an error */ An alternative would be to move sframe_add_section() to "[PATCH v11 04/15] unwind_user/sframe: Store sframe section data in per-mm maple tree" and reorder the patches as outlined below. > + ret = -ENOSYS; > + > +err_free: > + free_section(sec); > + return ret; > +} > + > +int sframe_remove_section(unsigned long sframe_start) > +{ > + return -ENOSYS; > +} I wonder whether the series should be restructured as follows: unwind_user/sframe: Store .sframe section data in per-mm maple tree unwind_user/sframe: Detect .sframe sections in executables unwind_user/sframe: Add support for reading .sframe headers unwind_user/sframe: Add support for reading .sframe contents unwind_user/sframe: Wire up unwind_user to sframe x86/uaccess: Add unsafe_copy_from_user() implementation unwind_user/sframe/x86: Enable sframe unwinding on x86 unwind_user: Stop when reaching an outermost frame unwind_user/sframe: Add support for outermost frame indication unwind_user/sframe: Remove .sframe section on detected corruption unwind_user/sframe: Show file name in debug output unwind_user/sframe: Add .sframe validation option unwind_user/sframe: Add prctl() interface for registering .sframe sections While moving sframe_add_section() and sframe_remove_section() from "unwind_user/sframe: Add support for reading .sframe headers" to "unwind_user/sframe: Store .sframe section data in per-mm maple tree" or into a new second patch, as they depend on the first and are required by the third. What are your thoughts? The reordering might be wasted effort. Thanks and regards, Jens -- Jens Remus Linux on Z Development (D3303) +49-7031-16-1128 Office jremus@de.ibm.com IBM IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Böblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294 IBM Data Privacy Statement: https://www.ibm.com/privacy/