[PATCH v3 16/21] kexec: fill note buffers by NT_VMCORE_PAD notes inpage-size boundary

From: HATAYAMA Daisuke
Date: Mon Mar 18 2013 - 22:32:56 EST

Fill both crash_notes and vmcoreinfo_note buffers by NT_VMCORE_PAD
note type to make them satisfy mmap()'s page-size boundary
requirement.

So far, end of note segments has been marked by zero-filled elf
header. Instead, this patch writes NT_VMCORE_PAD note in the end of
note segments until the offset on page-size boundary.

Also, old kernel can treat the ELF segments created without null
header because it stops reading ELF segments if real size it reads
reachs p_memsz.

Signed-off-by: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
---

arch/s390/include/asm/kexec.h | 8 ++++---
include/linux/kexec.h | 12 ++++++-----
kernel/kexec.c | 46 ++++++++++++++++++++++++++---------------
3 files changed, 41 insertions(+), 25 deletions(-)

diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
index 694bcd6..f33ec08 100644
--- a/arch/s390/include/asm/kexec.h
+++ b/arch/s390/include/asm/kexec.h
@@ -41,8 +41,8 @@
/*
* Size for s390x ELF notes per CPU
*
- * Seven notes plus zero note at the end: prstatus, fpregset, timer,
- * tod_cmp, tod_reg, control regs, and prefix
+ * Seven notes plus note with NT_VMCORE_PAD type at the end: prstatus,
+ * fpregset, timer, tod_cmp, tod_reg, control regs, and prefix
*/
#define KEXEC_NOTE_BYTES \
(ALIGN(sizeof(struct elf_note), 4) * 8 + \
@@ -53,7 +53,9 @@
ALIGN(sizeof(u64), 4) + \
ALIGN(sizeof(u32), 4) + \
ALIGN(sizeof(u64) * 16, 4) + \
- ALIGN(sizeof(u32), 4) \
+ ALIGN(sizeof(u32), 4) + \
+ KEXEC_CORE_NOTE_DESC_BYTES + \
+ VMCOREINFO_NOTE_NAME_BYTES \
)

/* Provide a dummy definition to avoid build failures. */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 5113570..6592935 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -47,14 +47,16 @@
#define KEXEC_CORE_NOTE_NAME_BYTES ALIGN(sizeof(KEXEC_CORE_NOTE_NAME), 4)
#define KEXEC_CORE_NOTE_DESC_BYTES ALIGN(sizeof(struct elf_prstatus), 4)
/*
- * The per-cpu notes area is a list of notes terminated by a "NULL"
- * note header. For kdump, the code in vmcore.c runs in the context
- * of the second kernel to combine them into one note.
+ * The per-cpu notes area is a list of notes terminated by a note
+ * header with NT_VMCORE_PAD type. For kdump, the code in vmcore.c
+ * runs in the context of the second kernel to combine them into one
+ * note.
*/
#ifndef KEXEC_NOTE_BYTES
#define KEXEC_NOTE_BYTES ( (KEXEC_NOTE_HEAD_BYTES * 2) + \
KEXEC_CORE_NOTE_NAME_BYTES + \
- KEXEC_CORE_NOTE_DESC_BYTES )
+ KEXEC_CORE_NOTE_DESC_BYTES + \
+ VMCOREINFO_NOTE_NAME_BYTES)
#endif

/*
@@ -187,7 +189,7 @@ extern struct kimage *kexec_crash_image;
#define VMCOREINFO_NOTE_NAME_BYTES ALIGN(sizeof(VMCOREINFO_NOTE_NAME), 4)
#define VMCOREINFO_NOTE_SIZE ALIGN(KEXEC_NOTE_HEAD_BYTES*2 \
+VMCOREINFO_BYTES \
- +VMCOREINFO_NOTE_NAME_BYTES, \
+ +VMCOREINFO_NOTE_NAME_BYTES*2, \
PAGE_SIZE)

/* Location of a reserved region to hold the crash kernel.
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 6597b82..fbdc0f0 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -40,6 +40,7 @@

/* Per cpu memory for storing cpu states in case of system crash. */
note_buf_t __percpu *crash_notes;
+static size_t crash_notes_size = ALIGN(sizeof(note_buf_t), PAGE_SIZE);

/* vmcoreinfo stuff */
static unsigned char vmcoreinfo_data[VMCOREINFO_BYTES];
@@ -1177,6 +1178,7 @@ unlock:
return ret;
}

+/* If @data is NULL, fill @buf with 0 in @data_len bytes. */
static u32 *append_elf_note(u32 *buf, char *name, unsigned type, void *data,
size_t data_len)
{
@@ -1189,26 +1191,36 @@ static u32 *append_elf_note(u32 *buf, char *name, unsigned type, void *data,
buf += (sizeof(note) + 3)/4;
memcpy(buf, name, note.n_namesz);
buf += (note.n_namesz + 3)/4;
- memcpy(buf, data, note.n_descsz);
+ if (data)
+ memcpy(buf, data, note.n_descsz);
+ else
+ memset(buf, 0, note.n_descsz);
buf += (note.n_descsz + 3)/4;

return buf;
}

-static void final_note(u32 *buf)
+static void final_note(u32 *buf, size_t buf_len, size_t data_len)
{
- struct elf_note note;
+ size_t used_bytes, pad_hdr_size;

- note.n_namesz = 0;
- note.n_descsz = 0;
- note.n_type = 0;
- memcpy(buf, &note, sizeof(note));
+ pad_hdr_size = KEXEC_NOTE_HEAD_BYTES + VMCOREINFO_NOTE_NAME_BYTES;
+
+ /*
+ * keep space for ELF note header and "VMCOREINFO" name to
+ * terminate ELF segment by NT_VMCORE_PAD note.
+ */
+ BUG_ON(data_len + pad_hdr_size > buf_len);
+
+ used_bytes = data_len + pad_hdr_size;
+ append_elf_note(buf, VMCOREINFO_NOTE_NAME, NT_VMCORE_PAD, NULL,
+ roundup(used_bytes, PAGE_SIZE) - used_bytes);
}

void crash_save_cpu(struct pt_regs *regs, int cpu)
{
struct elf_prstatus prstatus;
- u32 *buf;
+ u32 *buf, *buf_end;

if ((cpu < 0) || (cpu >= nr_cpu_ids))
return;
@@ -1226,16 +1238,15 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
memset(&prstatus, 0, sizeof(prstatus));
prstatus.pr_pid = current->pid;
elf_core_copy_kernel_regs(&prstatus.pr_reg, regs);
- buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
- &prstatus, sizeof(prstatus));
- final_note(buf);
+ buf_end = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
+ &prstatus, sizeof(prstatus));
+ final_note(buf_end, crash_notes_size, (buf_end - buf) * sizeof(u32));
}

static int __init crash_notes_memory_init(void)
{
/* Allocate memory for saving cpu registers. */
- crash_notes = __alloc_percpu(roundup(sizeof(note_buf_t), PAGE_SIZE),
- PAGE_SIZE);
+ crash_notes = __alloc_percpu(crash_notes_size, PAGE_SIZE);
if (!crash_notes) {
printk("Kexec: Memory allocation for saving cpu register"
" states failed\n");
@@ -1434,13 +1445,14 @@ int __init parse_crashkernel_low(char *cmdline,

static void update_vmcoreinfo_note(void)
{
- u32 *buf = vmcoreinfo_note;
+ u32 *buf = vmcoreinfo_note, *buf_end;

if (!vmcoreinfo_size)
return;
- buf = append_elf_note(buf, VMCOREINFO_NOTE_NAME, NT_VMCORE_DEBUGINFO,
- vmcoreinfo_data, vmcoreinfo_size);
- final_note(buf);
+ buf_end = append_elf_note(buf, VMCOREINFO_NOTE_NAME, NT_VMCORE_DEBUGINFO,
+ vmcoreinfo_data, vmcoreinfo_size);
+ final_note(buf_end, sizeof(vmcoreinfo_note),
+ (buf_end - buf) * sizeof(u32));
}

void crash_save_vmcoreinfo(void)

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