Message-ID: <20250422113156.575971-7-eugen.hristev@linaro.org>
Date: Tue, 22 Apr 2025 14:31:48 +0300
From: Eugen Hristev <eugen.hristev@...aro.org>
To: linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	andersson@...nel.org
Cc: linux-doc@...r.kernel.org,
	corbet@....net,
	tglx@...utronix.de,
	mingo@...hat.com,
	rostedt@...dmis.org,
	john.ogness@...utronix.de,
	senozhatsky@...omium.org,
	pmladek@...e.com,
	peterz@...radead.org,
	mojha@....qualcomm.com,
	linux-arm-kernel@...ts.infradead.org,
	vincent.guittot@...aro.org,
	konradybcio@...nel.org,
	dietmar.eggemann@....com,
	juri.lelli@...hat.com,
	eugen.hristev@...aro.org,
	Mukesh Ojha <quic_mojha@...cinc.com>
Subject: [RFC][PATCH 06/14] kmemdump: add coreimage ELF layer

Implement kmemdumping into an ELF coreimage.

Signed-off-by: Eugen Hristev <eugen.hristev@...aro.org>
Co-developed-by: Mukesh Ojha <quic_mojha@...cinc.com>
Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
---
 drivers/debug/Kconfig              |  10 +
 drivers/debug/Makefile             |   1 +
 drivers/debug/kmemdump.c           |  12 ++
 drivers/debug/kmemdump_coreimage.c | 285 +++++++++++++++++++++++++++++
 include/linux/kmemdump.h           |  25 +++
 5 files changed, 333 insertions(+)
 create mode 100644 drivers/debug/kmemdump_coreimage.c

diff --git a/drivers/debug/Kconfig b/drivers/debug/Kconfig
index 72a906487e02..cd73f299e5cd 100644
--- a/drivers/debug/Kconfig
+++ b/drivers/debug/Kconfig
@@ -14,6 +14,16 @@ config DRIVER_KMEMDUMP
 	  Note that modules using this feature must be rebuilt if option
 	  changes.
 
+config DRIVER_KMEMDUMP_COREIMAGE
+	depends on DRIVER_KMEMDUMP
+	bool "Assemble memory regions into a coredump readable with debuggers"
+	help
+	  Enabling this will assemble all the memory regions into a
+	  core ELF file. The first region will include program headers for
+	  all the regions, together with vmcoreinfo and specific coredump
+	  structures. The coredump file can then be loaded into GDB or crash
+	  tool and further inspected.
+
 config QCOM_MD_KMEMDUMP_BACKEND
 	tristate "Qualcomm Minidump kmemdump backend driver"
 	depends on ARCH_QCOM || COMPILE_TEST
diff --git a/drivers/debug/Makefile b/drivers/debug/Makefile
index d8a9db29cd15..95ecc315b376 100644
--- a/drivers/debug/Makefile
+++ b/drivers/debug/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_DRIVER_KMEMDUMP) += kmemdump.o
+obj-$(CONFIG_DRIVER_KMEMDUMP_COREIMAGE) += kmemdump_coreimage.o
 obj-$(CONFIG_QCOM_MD_KMEMDUMP_BACKEND) += qcom_md.o
diff --git a/drivers/debug/kmemdump.c b/drivers/debug/kmemdump.c
index a685c0863e25..be96b39a136a 100644
--- a/drivers/debug/kmemdump.c
+++ b/drivers/debug/kmemdump.c
@@ -58,6 +58,7 @@ int kmemdump_register(char *handle, void *zone, size_t size)
 			return ret;
 		}
 		z->registered = true;
+		update_elfheader(z);
 	}
 
 	mutex_unlock(&kmemdump_lock);
@@ -84,6 +85,7 @@ void kmemdump_unregister(int id)
 	if (z->registered && backend)
 		backend->unregister_region(z->id);
 
+	clear_elfheader(z);
 	idr_remove(&kmemdump_idr, id);
 	kfree(z);
 
@@ -103,6 +105,7 @@ static int kmemdump_register_fn(int id, void *p, void *data)
 	if (ret)
 		return ret;
 	z->registered = true;
+	update_elfheader(z);
 
 	return 0;
 }
@@ -130,6 +133,14 @@ int kmemdump_register_backend(struct kmemdump_backend *be)
 	pr_info("kmemdump backend %s registered successfully.\n",
 		backend->name);
 
+	init_elfheader(backend);
+
+	mutex_unlock(&kmemdump_lock);
+
+	register_coreinfo();
+
+	mutex_lock(&kmemdump_lock);
+
 	/* Try to call the backend for all previously requested zones */
 	idr_for_each(&kmemdump_idr, kmemdump_register_fn, NULL);
 
@@ -151,6 +162,7 @@ static int kmemdump_unregister_fn(int id, void *p, void *data)
 	if (ret)
 		return ret;
 	z->registered = false;
+	clear_elfheader(z);
 
 	return 0;
 }
diff --git a/drivers/debug/kmemdump_coreimage.c b/drivers/debug/kmemdump_coreimage.c
new file mode 100644
index 000000000000..59630adf5dd2
--- /dev/null
+++ b/drivers/debug/kmemdump_coreimage.c
@@ -0,0 +1,285 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/init.h>
+#include <linux/elfcore.h>
+#include <linux/kmemdump.h>
+#include <linux/utsname.h>
+#include <linux/sched/stat.h>
+#include <linux/vmcore_info.h>
+
+#define CORE_STR "CORE"
+#define KMEMDUMP_ELF_ID 0
+
+#define MAX_NUM_ENTRIES	  201
+
+/**
+ * struct kmemdump_elfhdr - Kmemdump table elf header
+ * @ehdr: elf main header
+ * @phdr: Program header
+ * @elf_offset: Section offset in elf
+ */
+struct kmemdump_elfhdr {
+	struct elfhdr	 *ehdr;
+	struct elf_phdr	 *phdr;
+	size_t		 elf_offset;
+} elf;
+
+extern char kernel_config_data;
+
+/**
+ * register_coreinfo() - Register vital kernel information into the coreimage
+ *
+ * Return: None
+ */
+void register_coreinfo(void)
+{
+	/*
+	 * Right before kernel_config_data there is a marker string,
+	 * capture it as well.
+	 * Debug tools don't care about config size, they just try 64K and
+	 * if it's not enough, double it.
+	 */
+	kmemdump_register("config", (void *)&kernel_config_data - 8,
+			  128 * 1024);
+	kmemdump_register("utsn", (void *)&init_uts_ns,
+			  sizeof(init_uts_ns));
+	kmemdump_register("banner", (void *)&linux_banner,
+			  strlen(linux_banner));
+	kmemdump_register("percpu", (void *)&__per_cpu_offset,
+			  sizeof(__per_cpu_offset));
+	kmemdump_register("init_mm", (void *)&init_mm,
+			  sizeof(init_mm));
+	kmemdump_register("mmpgd", (void *)init_mm.pgd,
+			  sizeof(*init_mm.pgd));
+	kmemdump_register("highmem", (void *)&high_memory,
+			  sizeof(&high_memory));
+	kmemdump_register("memsect", (void *)*mem_section,
+			  sizeof(struct mem_section) * NR_SECTION_ROOTS);
+	kmemdump_register("memsect", (void *)&mem_section,
+			  sizeof(&mem_section));
+	kmemdump_register("totalram", (void *)&_totalram_pages,
+			  sizeof(_totalram_pages));
+	kmemdump_register("node_states", (void *)&node_states,
+			  sizeof(node_states));
+	kmemdump_register("nr_threads", (void *)&nr_threads,
+			  sizeof(nr_threads));
+	kmemdump_register("cpu_po", (void *)cpu_possible_mask,
+			  sizeof(cpumask_t));
+	kmemdump_register("cpu_pr", (void *)cpu_present_mask,
+			  sizeof(cpumask_t));
+	kmemdump_register("cpu_on", (void *)cpu_online_mask,
+			  sizeof(cpumask_t));
+	kmemdump_register("jiffies", (void *)&jiffies_64,
+			  sizeof(jiffies_64));
+}
+
+static struct elf_phdr *elf_phdr_entry_addr(struct elfhdr *ehdr, int idx)
+{
+	struct elf_phdr *ephdr = (struct elf_phdr *)((size_t)ehdr + ehdr->e_phoff);
+
+	return &ephdr[idx];
+}
+
+/**
+ * clear_elfheader() - Remove the program header for a specific memory zone
+ * @z: pointer to the kmemdump zone
+ *
+ * Return: On success, it returns 0, errno otherwise
+ */
+int clear_elfheader(const struct kmemdump_zone *z)
+{
+	struct elfhdr *ehdr = elf.ehdr;
+	struct elf_phdr *phdr;
+	struct elf_phdr *tmp_phdr;
+	unsigned int phidx;
+	unsigned int i;
+
+	for (i = 0; i < ehdr->e_phnum; i++) {
+		phdr = elf_phdr_entry_addr(ehdr, i);
+		if (phdr->p_paddr == virt_to_phys(z->zone) &&
+		    phdr->p_memsz == ALIGN(z->size, 4))
+			break;
+	}
+
+	if (i == ehdr->e_phnum) {
+		pr_err("Cannot find program header entry in elf\n");
+		return -EINVAL;
+	}
+
+	phidx = i;
+
+	/* Clear program header */
+	tmp_phdr = elf_phdr_entry_addr(ehdr, phidx);
+	for (i = phidx; i < ehdr->e_phnum - 1; i++) {
+		tmp_phdr = elf_phdr_entry_addr(ehdr, i + 1);
+		phdr = elf_phdr_entry_addr(ehdr, i);
+		memcpy(phdr, tmp_phdr, sizeof(*phdr));
+		phdr->p_offset = phdr->p_offset - ALIGN(z->size, 4);
+	}
+	memset(tmp_phdr, 0, sizeof(*tmp_phdr));
+	ehdr->e_phnum--;
+
+	elf.elf_offset -= ALIGN(z->size, 4);
+
+	return 0;
+}
+
+/**
+ * update_elfheader() - Add the program header for a specific memory zone
+ * @z: pointer to the kmemdump zone
+ *
+ * Return: None
+ */
+void update_elfheader(const struct kmemdump_zone *z)
+{
+	struct elfhdr *ehdr = elf.ehdr;
+	struct elf_phdr *phdr;
+
+	phdr = elf_phdr_entry_addr(ehdr, ehdr->e_phnum++);
+
+	phdr->p_type = PT_LOAD;
+	phdr->p_offset = elf.elf_offset;
+	phdr->p_vaddr = (elf_addr_t)z->zone;
+	phdr->p_paddr = (elf_addr_t)virt_to_phys(z->zone);
+	phdr->p_filesz = phdr->p_memsz = ALIGN(z->size, 4);
+	phdr->p_flags = PF_R | PF_W;
+
+	elf.elf_offset += ALIGN(z->size, 4);
+}
+
+static void append_kcore_note(char *notes, size_t *i, const char *name,
+			      unsigned int type, const void *desc,
+			      size_t descsz)
+{
+	struct elf_note *note = (struct elf_note *)&notes[*i];
+
+	note->n_namesz = strlen(name) + 1;
+	note->n_descsz = descsz;
+	note->n_type = type;
+	*i += sizeof(*note);
+	memcpy(&notes[*i], name, note->n_namesz);
+	*i = ALIGN(*i + note->n_namesz, 4);
+	memcpy(&notes[*i], desc, descsz);
+	*i = ALIGN(*i + descsz, 4);
+}
+
+static void append_kcore_note_nodesc(char *notes, size_t *i, const char *name,
+				     unsigned int type, size_t descsz)
+{
+	struct elf_note *note = (struct elf_note *)&notes[*i];
+
+	note->n_namesz = strlen(name) + 1;
+	note->n_descsz = descsz;
+	note->n_type = type;
+	*i += sizeof(*note);
+	memcpy(&notes[*i], name, note->n_namesz);
+	*i = ALIGN(*i + note->n_namesz, 4);
+}
+
+/**
+ * init_elfheader() - Prepare coreinfo elf header
+ *		This function prepares the elf header for the coredump image.
+ *		Initially there is a single program header for the elf NOTE.
+ *		The note contains the usual core dump information, and the
+ *		vmcoreinfo.
+ * @z: pointer to the kmemdump zone
+ *
+ * Return: 0 on success, errno otherwise
+ */
+int init_elfheader(struct kmemdump_backend *be)
+{
+	struct elfhdr *ehdr;
+	struct elf_phdr *phdr;
+	void *notes;
+	unsigned int elfh_size;
+	unsigned int phdr_off;
+	size_t note_len, i = 0;
+
+	struct elf_prstatus prstatus = {};
+	struct elf_prpsinfo prpsinfo = {
+		.pr_sname = 'R',
+		.pr_fname = "vmlinux",
+	};
+
+	/*
+	 * Header buffer contains:
+	 * ELF header, Note entry with PR status, PR ps info, and vmcoreinfo
+	 * MAX_NUM_ENTRIES Program headers,
+	 */
+	elfh_size = sizeof(*ehdr);
+	elfh_size += sizeof(struct elf_prstatus);
+	elfh_size += sizeof(struct elf_prpsinfo);
+	elfh_size += sizeof(VMCOREINFO_NOTE_NAME);
+	elfh_size += ALIGN(vmcoreinfo_size, 4);
+	elfh_size += (sizeof(*phdr)) * (MAX_NUM_ENTRIES);
+
+	elfh_size = ALIGN(elfh_size, 4);
+
+	elf.ehdr = kzalloc(elfh_size, GFP_KERNEL);
+	if (!elf.ehdr)
+		return -ENOMEM;
+
+	ehdr = elf.ehdr;
+	/* Assign Program headers offset, it's right after the elf header. */
+	elf.phdr = phdr = (struct elf_phdr *)(ehdr + 1);
+	phdr_off = sizeof(*ehdr);
+
+	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
+	ehdr->e_ident[EI_CLASS] = ELF_CLASS;
+	ehdr->e_ident[EI_DATA] = ELF_DATA;
+	ehdr->e_ident[EI_VERSION] = EV_CURRENT;
+	ehdr->e_ident[EI_OSABI] = ELF_OSABI;
+	ehdr->e_type = ET_CORE;
+	ehdr->e_machine  = ELF_ARCH;
+	ehdr->e_version = EV_CURRENT;
+	ehdr->e_ehsize = sizeof(*ehdr);
+	ehdr->e_phentsize = sizeof(*phdr);
+
+	elf.elf_offset = elfh_size;
+
+	notes = (void *)(((char *)elf.ehdr) + elf.elf_offset);
+
+	/* we have a single program header now */
+	ehdr->e_phnum = 1;
+
+	/* Length of the note is made of :
+	 * 3 elf notes structs (prstatus, prpsinfo, vmcoreinfo)
+	 * 3 notes names (2 core strings, 1 vmcoreinfo name)
+	 * sizeof each note
+	 */
+	note_len = (3 * sizeof(struct elf_note) +
+		    2 * ALIGN(sizeof(CORE_STR), 4) +
+		    VMCOREINFO_NOTE_NAME_BYTES +
+		    ALIGN(sizeof(struct elf_prstatus), 4) +
+		    ALIGN(sizeof(struct elf_prpsinfo), 4) +
+		    ALIGN(vmcoreinfo_size, 4));
+
+	phdr->p_type = PT_NOTE;
+	phdr->p_offset = elf.elf_offset;
+	phdr->p_filesz = note_len;
+
+	/* advance elf offset */
+	elf.elf_offset += note_len;
+
+	strscpy(prpsinfo.pr_psargs, saved_command_line,
+		sizeof(prpsinfo.pr_psargs));
+
+	append_kcore_note(notes, &i, CORE_STR, NT_PRSTATUS, &prstatus,
+			  sizeof(prstatus));
+	append_kcore_note(notes, &i, CORE_STR, NT_PRPSINFO, &prpsinfo,
+			  sizeof(prpsinfo));
+	append_kcore_note_nodesc(notes, &i, VMCOREINFO_NOTE_NAME, 0,
+				 ALIGN(vmcoreinfo_size, 4));
+
+	ehdr->e_phoff = phdr_off;
+
+	/* This is the first kmemdump region, the ELF header */
+	be->register_region(KMEMDUMP_ELF_ID, "ELF", elf.ehdr,
+			    elfh_size + note_len - ALIGN(vmcoreinfo_size, 4));
+
+	/* The second region is the vmcoreinfo, which goes right after */
+	be->register_region(KMEMDUMP_ELF_ID, "vmcoreinfo", vmcoreinfo_data,
+			    ALIGN(vmcoreinfo_size, 4));
+
+	return 0;
+}
diff --git a/include/linux/kmemdump.h b/include/linux/kmemdump.h
index b55b15c295ac..13aabd72d17a 100644
--- a/include/linux/kmemdump.h
+++ b/include/linux/kmemdump.h
@@ -49,4 +49,29 @@ static inline void kmemdump_unregister(int id)
 
 int kmemdump_register_backend(struct kmemdump_backend *backend);
 void kmemdump_unregister_backend(struct kmemdump_backend *backend);
+
+#ifdef CONFIG_DRIVER_KMEMDUMP_COREIMAGE
+int init_elfheader(struct kmemdump_backend *be);
+void update_elfheader(const struct kmemdump_zone *z);
+int clear_elfheader(const struct kmemdump_zone *z);
+void register_coreinfo(void);
+#else
+static inline int init_elfheader(struct kmemdump_backend *be)
+{
+	return 0;
+}
+
+static inline void update_elfheader(const struct kmemdump_zone *z)
+{
+}
+
+static inline int clear_elfheader(const struct kmemdump_zone *z)
+{
+	return 0;
+}
+
+static inline void register_coreinfo(void)
+{
+}
+#endif
 #endif
-- 
2.43.0

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