[PATCH net-next v4 2/3] vmcore: append device dumps to vmcore as elf notes

[Rahul Lakkireddy]

Update read and mmap logic to append device dumps as additional notes
before the other elf notes. We add device dumps before other elf notes
because the other elf notes may not fill the elf notes buffer
completely and we will end up with zero-filled data between the elf
notes and the device dumps. Tools will then try to decode this
zero-filled data as valid notes and we don't want that. Hence, adding
device dumps before the other elf notes ensure that zero-filled data
can be avoided. This also ensures that the device dumps and the
other elf notes can be properly mmaped at page aligned address.

Incorporate device dump size into the total vmcore size. Also update
offsets for other program headers after the device dumps are added.

Suggested-by: Eric Biederman <ebiederm@xxxxxxxxxxxx>.
Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@xxxxxxxxxxx>
Signed-off-by: Ganesh Goudar <ganeshgr@xxxxxxxxxxx>
---
v4:
- No changes.

v3:
- Patch added in this version.
- Exported dumps as elf notes. Suggested by Eric Biederman
  <ebiederm@xxxxxxxxxxxx>.

 fs/proc/vmcore.c | 247 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 243 insertions(+), 4 deletions(-)

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 7395462d2f86..ed1ebd85e14e 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -39,6 +39,8 @@ static size_t elfcorebuf_sz_orig;
 
 static char *elfnotes_buf;
 static size_t elfnotes_sz;
+/* Size of all notes minus the device dump notes */
+static size_t elfnotes_orig_sz;
 
 /* Total size of vmcore file. */
 static u64 vmcore_size;
@@ -51,6 +53,9 @@ static LIST_HEAD(vmcoredd_list);
 static DEFINE_MUTEX(vmcoredd_mutex);
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
+/* Device Dump Size */
+static size_t vmcoredd_orig_sz;
+
 /*
  * Returns > 0 for RAM pages, 0 for non-RAM pages, < 0 on error
  * The called function has to take care of module refcounting.
@@ -185,6 +190,77 @@ static int copy_to(void *target, void *src, size_t size, int userbuf)
 	return 0;
 }
 
+#ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
+static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
+{
+	struct vmcoredd_node *dump;
+	u64 offset = 0;
+	int ret = 0;
+	size_t tsz;
+	char *buf;
+
+	mutex_lock(&vmcoredd_mutex);
+	list_for_each_entry(dump, &vmcoredd_list, list) {
+		if (start < offset + dump->size) {
+			tsz = min(offset + (u64)dump->size - start, (u64)size);
+			buf = dump->buf + start - offset;
+			if (copy_to(dst, buf, tsz, userbuf)) {
+				ret = -EFAULT;
+				goto out_unlock;
+			}
+
+			size -= tsz;
+			start += tsz;
+			dst += tsz;
+
+			/* Leave now if buffer filled already */
+			if (!size)
+				goto out_unlock;
+		}
+		offset += dump->size;
+	}
+
+out_unlock:
+	mutex_unlock(&vmcoredd_mutex);
+	return ret;
+}
+
+static int vmcoredd_mmap_dumps(struct vm_area_struct *vma, unsigned long dst,
+			       u64 start, size_t size)
+{
+	struct vmcoredd_node *dump;
+	u64 offset = 0;
+	int ret = 0;
+	size_t tsz;
+	char *buf;
+
+	mutex_lock(&vmcoredd_mutex);
+	list_for_each_entry(dump, &vmcoredd_list, list) {
+		if (start < offset + dump->size) {
+			tsz = min(offset + (u64)dump->size - start, (u64)size);
+			buf = dump->buf + start - offset;
+			if (remap_vmalloc_range_partial(vma, dst, buf, tsz)) {
+				ret = -EFAULT;
+				goto out_unlock;
+			}
+
+			size -= tsz;
+			start += tsz;
+			dst += tsz;
+
+			/* Leave now if buffer filled already */
+			if (!size)
+				goto out_unlock;
+		}
+		offset += dump->size;
+	}
+
+out_unlock:
+	mutex_unlock(&vmcoredd_mutex);
+	return ret;
+}
+#endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
+
 /* Read from the ELF header and then the crash dump. On error, negative value is
  * returned otherwise number of bytes read are returned.
  */
@@ -222,10 +298,41 @@ static ssize_t __read_vmcore(char *buffer, size_t buflen, loff_t *fpos,
 	if (*fpos < elfcorebuf_sz + elfnotes_sz) {
 		void *kaddr;
 
+		/* We add device dumps before other elf notes because the
+		 * other elf notes may not fill the elf notes buffer
+		 * completely and we will end up with zero-filled data
+		 * between the elf notes and the device dumps. Tools will
+		 * then try to decode this zero-filled data as valid notes
+		 * and we don't want that. Hence, adding device dumps before
+		 * the other elf notes ensure that zero-filled data can be
+		 * avoided.
+		 */
+#ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
+		/* Read device dumps */
+		if (*fpos < elfcorebuf_sz + vmcoredd_orig_sz) {
+			tsz = min(elfcorebuf_sz + vmcoredd_orig_sz -
+				  (size_t)*fpos, buflen);
+			start = *fpos - elfcorebuf_sz;
+			if (vmcoredd_copy_dumps(buffer, start, tsz, userbuf))
+				return -EFAULT;
+
+			buflen -= tsz;
+			*fpos += tsz;
+			buffer += tsz;
+			acc += tsz;
+
+			/* leave now if filled buffer already */
+			if (!buflen)
+				return acc;
+		}
+#endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
+
+		/* Read remaining elf notes */
 		tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)*fpos, buflen);
-		kaddr = elfnotes_buf + *fpos - elfcorebuf_sz;
+		kaddr = elfnotes_buf + *fpos - elfcorebuf_sz - vmcoredd_orig_sz;
 		if (copy_to(buffer, kaddr, tsz, userbuf))
 			return -EFAULT;
+
 		buflen -= tsz;
 		*fpos += tsz;
 		buffer += tsz;
@@ -451,11 +558,46 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
 	if (start < elfcorebuf_sz + elfnotes_sz) {
 		void *kaddr;
 
+		/* We add device dumps before other elf notes because the
+		 * other elf notes may not fill the elf notes buffer
+		 * completely and we will end up with zero-filled data
+		 * between the elf notes and the device dumps. Tools will
+		 * then try to decode this zero-filled data as valid notes
+		 * and we don't want that. Hence, adding device dumps before
+		 * the other elf notes ensure that zero-filled data can be
+		 * avoided. This also ensures that the device dumps and
+		 * other elf notes can be properly mmaped at page aligned
+		 * address.
+		 */
+#ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
+		/* Read device dumps */
+		if (start < elfcorebuf_sz + vmcoredd_orig_sz) {
+			u64 start_off;
+
+			tsz = min(elfcorebuf_sz + vmcoredd_orig_sz -
+				  (size_t)start, size);
+			start_off = start - elfcorebuf_sz;
+			if (vmcoredd_mmap_dumps(vma, vma->vm_start + len,
+						start_off, tsz))
+				goto fail;
+
+			size -= tsz;
+			start += tsz;
+			len += tsz;
+
+			/* leave now if filled buffer already */
+			if (!size)
+				return 0;
+		}
+#endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
+
+		/* Read remaining elf notes */
 		tsz = min(elfcorebuf_sz + elfnotes_sz - (size_t)start, size);
-		kaddr = elfnotes_buf + start - elfcorebuf_sz;
+		kaddr = elfnotes_buf + start - elfcorebuf_sz - vmcoredd_orig_sz;
 		if (remap_vmalloc_range_partial(vma, vma->vm_start + len,
 						kaddr, tsz))
 			goto fail;
+
 		size -= tsz;
 		start += tsz;
 		len += tsz;
@@ -703,6 +845,11 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
 	/* Modify e_phnum to reflect merged headers. */
 	ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
 
+	/* Store the size of all notes.  We need this to update the note
+	 * header when the device dumps will be added.
+	 */
+	elfnotes_orig_sz = phdr.p_memsz;
+
 	return 0;
 }
 
@@ -889,6 +1036,11 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
 	/* Modify e_phnum to reflect merged headers. */
 	ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
 
+	/* Store the size of all notes.  We need this to update the note
+	 * header when the device dumps will be added.
+	 */
+	elfnotes_orig_sz = phdr.p_memsz;
+
 	return 0;
 }
 
@@ -981,8 +1133,8 @@ static int __init process_ptload_program_headers_elf32(char *elfptr,
 }
 
 /* Sets offset fields of vmcore elements. */
-static void __init set_vmcore_list_offsets(size_t elfsz, size_t elfnotes_sz,
-					   struct list_head *vc_list)
+static void set_vmcore_list_offsets(size_t elfsz, size_t elfnotes_sz,
+				    struct list_head *vc_list)
 {
 	loff_t vmcore_off;
 	struct vmcore *m;
@@ -1188,6 +1340,92 @@ static void vmcoredd_write_note(const char *name, void *buf, size_t size)
 		 name);
 }
 
+/**
+ * vmcoredd_update_program_headers - Update all Elf program headers
+ * @elfptr: Pointer to elf header
+ * @elfnotesz: Size of elf notes aligned to page size
+ * @vmcoreddsz: Size of device dumps to be added to elf note header
+ *
+ * Determine type of Elf header (Elf64 or Elf32) and update the elf note size.
+ * Also update the offsets of all the program headers after the elf note header.
+ */
+static void vmcoredd_update_program_headers(char *elfptr, size_t elfnotesz,
+					    size_t vmcoreddsz)
+{
+	unsigned char *e_ident = (unsigned char *)elfptr;
+	u64 start, end, size;
+	loff_t vmcore_off;
+	u32 i;
+
+	vmcore_off = elfcorebuf_sz + elfnotesz;
+
+	if (e_ident[EI_CLASS] == ELFCLASS64) {
+		Elf64_Ehdr *ehdr = (Elf64_Ehdr *)elfptr;
+		Elf64_Phdr *phdr = (Elf64_Phdr *)(elfptr + sizeof(Elf64_Ehdr));
+
+		/* Update all program headers */
+		for (i = 0; i < ehdr->e_phnum; i++, phdr++) {
+			if (phdr->p_type == PT_NOTE) {
+				/* Update note size */
+				phdr->p_memsz = elfnotes_orig_sz + vmcoreddsz;
+				phdr->p_filesz = phdr->p_memsz;
+				continue;
+			}
+
+			start = rounddown(phdr->p_offset, PAGE_SIZE);
+			end = roundup(phdr->p_offset + phdr->p_memsz,
+				      PAGE_SIZE);
+			size = end - start;
+			phdr->p_offset = vmcore_off + (phdr->p_offset - start);
+			vmcore_off += size;
+		}
+	} else {
+		Elf32_Ehdr *ehdr = (Elf32_Ehdr *)elfptr;
+		Elf32_Phdr *phdr = (Elf32_Phdr *)(elfptr + sizeof(Elf32_Ehdr));
+
+		/* Update all program headers */
+		for (i = 0; i < ehdr->e_phnum; i++, phdr++) {
+			if (phdr->p_type == PT_NOTE) {
+				/* Update note size */
+				phdr->p_memsz = elfnotes_orig_sz + vmcoreddsz;
+				phdr->p_filesz = phdr->p_memsz;
+				continue;
+			}
+
+			start = rounddown(phdr->p_offset, PAGE_SIZE);
+			end = roundup(phdr->p_offset + phdr->p_memsz,
+				      PAGE_SIZE);
+			size = end - start;
+			phdr->p_offset = vmcore_off + (phdr->p_offset - start);
+			vmcore_off += size;
+		}
+	}
+}
+
+/**
+ * vmcoredd_update_size - Update the total size of the device dumps and update
+ * Elf header
+ * @dump_size: Size of the current device dump to be added to total size
+ *
+ * Update the total size of all the device dumps and update the Elf program
+ * headers. Calculate the new offsets for the vmcore list and update the
+ * total vmcore size.
+ */
+static void vmcoredd_update_size(size_t dump_size)
+{
+	vmcoredd_orig_sz += dump_size;
+	elfnotes_sz = roundup(elfnotes_orig_sz, PAGE_SIZE) + vmcoredd_orig_sz;
+	vmcoredd_update_program_headers(elfcorebuf, elfnotes_sz,
+					vmcoredd_orig_sz);
+
+	/* Update vmcore list offsets */
+	set_vmcore_list_offsets(elfcorebuf_sz, elfnotes_sz, &vmcore_list);
+
+	vmcore_size = get_vmcore_size(elfcorebuf_sz, elfnotes_sz,
+				      &vmcore_list);
+	proc_vmcore->size = vmcore_size;
+}
+
 /**
  * vmcore_add_device_dump - Add a buffer containing device dump to vmcore
  * @data: dump info.
@@ -1239,6 +1477,7 @@ static int __vmcore_add_device_dump(struct vmcoredd_data *data)
 	list_add_tail(&dump->list, &vmcoredd_list);
 	mutex_unlock(&vmcoredd_mutex);
 
+	vmcoredd_update_size(data_size);
 	return 0;
 
 out_err:
-- 
2.14.1