crash/0005-diskdump-netdump-fix-segmentation-fault-caused-by-fa.patch

From db8c030857b4e318728c51c20da687906c109d0d Mon Sep 17 00:00:00 2001
From: HATAYAMA Daisuke <d.hatayama@fujitsu.com>
Date: Tue, 30 May 2023 19:38:34 +0900
Subject: [PATCH 05/13] diskdump/netdump: fix segmentation fault caused by
 failure of stopping CPUs

There's no NMI on ARM. Hence, stopping the non-panicking CPUs from the
panicking CPU via IPI can fail easily if interrupts are being masked
in those moment. Moreover, crash_notes are not initialized for such
unstopped CPUs and the corresponding NT_PRSTATUS notes are not
attached to vmcore. However, crash utility never takes it
consideration such uninitialized crash_notes and then ends with
mapping different NT_PRSTATUS to actually unstopped CPUs. This corrupt
mapping can result crash utility into segmentation fault in the
operations where register values in NT_PRSTATUS notes are used.

For example:

    crash> bt 1408
    PID: 1408     TASK: ffff000003e22200  CPU: 2    COMMAND: "repro"
    Segmentation fault (core dumped)

    crash> help -D
    diskdump_data:
		      filename: 127.0.0.1-2023-05-26-02:21:27/vmcore-ld1
			     flags: 46 (KDUMP_CMPRS_LOCAL|ERROR_EXCLUDED|LZO_SUPPORTED)
    ...snip...
		       notes_buf: 1815df0
      num_vmcoredd_notes: 0
      num_prstatus_notes: 5
			    notes[0]: 1815df0 (NT_PRSTATUS)
					      si.signo: 0  si.code: 0  si.errno: 0
    ...snip...
					      PSTATE: 80400005   FPVALID: 00000000
			    notes[4]: 1808f10 (NT_PRSTATUS)
    Segmentation fault (core dumped)

To fix this issue, let's map NT_PRSTATUS to some CPU only if the
corresponding crash_notes is checked to be initialized.

[ kh: moved existence check for crash_notes out of the loop ]

Signed-off-by: HATAYAMA Daisuke <d.hatayama@fujitsu.com>
Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>
Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
---
 defs.h     |  1 +
 diskdump.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 netdump.c  |  7 ++++++-
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/defs.h b/defs.h
index 7d8bb8ab3de1..6520d2f13f48 100644
--- a/defs.h
+++ b/defs.h
@@ -7118,6 +7118,7 @@ int dumpfile_is_split(void);
 void show_split_dumpfiles(void);
 void x86_process_elf_notes(void *, unsigned long);
 void *diskdump_get_prstatus_percpu(int);
+int have_crash_notes(int cpu);
 void map_cpus_to_prstatus_kdump_cmprs(void);
 void diskdump_display_regs(int, FILE *);
 void process_elf32_notes(void *, ulong);
diff --git a/diskdump.c b/diskdump.c
index 94bca4ded572..2c284ff3f97f 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -101,12 +101,54 @@ int dumpfile_is_split(void)
 	return KDUMP_SPLIT();
 }
 
+int have_crash_notes(int cpu)
+{
+	ulong crash_notes, notes_ptr;
+	char *buf, *p;
+	Elf64_Nhdr *note = NULL;
+
+	if (!readmem(symbol_value("crash_notes"), KVADDR, &crash_notes,
+		     sizeof(crash_notes), "crash_notes", RETURN_ON_ERROR)) {
+		error(WARNING, "cannot read \"crash_notes\"\n");
+		return FALSE;
+	}
+
+	if ((kt->flags & SMP) && (kt->flags & PER_CPU_OFF))
+		notes_ptr = crash_notes + kt->__per_cpu_offset[cpu];
+	else
+		notes_ptr = crash_notes;
+
+	buf = GETBUF(SIZE(note_buf));
+
+	if (!readmem(notes_ptr, KVADDR, buf,
+		     SIZE(note_buf), "note_buf_t", RETURN_ON_ERROR)) {
+		error(WARNING, "cpu %d: cannot read NT_PRSTATUS note\n", cpu);
+		return FALSE;
+	}
+
+	note = (Elf64_Nhdr *)buf;
+	p = buf + sizeof(Elf64_Nhdr);
+
+	if (note->n_type != NT_PRSTATUS) {
+		error(WARNING, "cpu %d: invalid NT_PRSTATUS note (n_type != NT_PRSTATUS)\n", cpu);
+		return FALSE;
+	}
+
+	if (!STRNEQ(p, "CORE")) {
+		error(WARNING, "cpu %d: invalid NT_PRSTATUS note (name != \"CORE\")\n", cpu);
+		return FALSE;
+	}
+
+	return TRUE;
+}
+
 void
 map_cpus_to_prstatus_kdump_cmprs(void)
 {
 	void **nt_ptr;
 	int online, i, j, nrcpus;
 	size_t size;
+	int crash_notes_exists;
 
 	if (pc->flags2 & QEMU_MEM_DUMP_COMPRESSED)  /* notes exist for all cpus */
 		goto resize_note_pointers;
@@ -129,9 +171,10 @@ map_cpus_to_prstatus_kdump_cmprs(void)
 	 *  Re-populate the array with the notes mapping to online cpus
 	 */
 	nrcpus = (kt->kernel_NR_CPUS ? kt->kernel_NR_CPUS : NR_CPUS);
+	crash_notes_exists = kernel_symbol_exists("crash_notes");
 
 	for (i = 0, j = 0; i < nrcpus; i++) {
-		if (in_cpu_map(ONLINE_MAP, i)) {
+		if (in_cpu_map(ONLINE_MAP, i) && (!crash_notes_exists || have_crash_notes(i))) {
 			dd->nt_prstatus_percpu[i] = nt_ptr[j++];
 			dd->num_prstatus_notes = 
 				MAX(dd->num_prstatus_notes, i+1);
diff --git a/netdump.c b/netdump.c
index 4eba66cecb55..61ddeaa08831 100644
--- a/netdump.c
+++ b/netdump.c
@@ -75,6 +75,7 @@ map_cpus_to_prstatus(void)
 	void **nt_ptr;
 	int online, i, j, nrcpus;
 	size_t size;
+	int crash_notes_exists;
 
 	if (pc->flags2 & QEMU_MEM_DUMP_ELF)  /* notes exist for all cpus */
 		return;
@@ -97,10 +98,14 @@ map_cpus_to_prstatus(void)
 	 *  Re-populate the array with the notes mapping to online cpus
 	 */
 	nrcpus = (kt->kernel_NR_CPUS ? kt->kernel_NR_CPUS : NR_CPUS);
+	crash_notes_exists = kernel_symbol_exists("crash_notes");
 
 	for (i = 0, j = 0; i < nrcpus; i++) {
-		if (in_cpu_map(ONLINE_MAP, i))
+		if (in_cpu_map(ONLINE_MAP, i) && (!crash_notes_exists || have_crash_notes(i))) {
 			nd->nt_prstatus_percpu[i] = nt_ptr[j++];
+			nd->num_prstatus_notes =
+				MAX(nd->num_prstatus_notes, i+1);
+		}
 	}
 
 	FREEBUF(nt_ptr);
-- 
2.37.1