s390/crash: Do not use VM info if os_info does not have it

The virtual memory information stored in os_info area is
required for creation of the kernel image PT_LOAD program
header for kernels since commit a2ec5bec56dd ("s390/mm:
uncouple physical vs virtual address spaces").

By contrast, if such information in os_info is absent the
PT_LOAD program header should not be created.

Currently the proper PT_LOAD program header is created for
kernels that contain the virtual memory information, but
for kernels without one an invalid header of zero size is
created. That in turn leads to stand-alone dump failures.

Use OS_INFO_KASLR_OFFSET variable to check whether os_info
is present or not (same as crash and makedumpfile tools do)
and based on that create or do not create the kernel image
PT_LOAD program header.

Fixes: f4cac27 ("s390/crash: Use old os_info to create PT_LOAD headers")
Tested-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Acked-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

Author: Alexander Gordeev

arch/s390/kernel/crash_dump.c

@@ -451,7 +451,7 @@ static void *nt_final(void *ptr)
 /*
  * Initialize ELF header (new kernel)
  */
-static void *ehdr_init(Elf64_Ehdr *ehdr, int mem_chunk_cnt)
+static void *ehdr_init(Elf64_Ehdr *ehdr, int phdr_count)
 {
 	memset(ehdr, 0, sizeof(*ehdr));
 	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
@@ -465,11 +465,8 @@ static void *ehdr_init(Elf64_Ehdr *ehdr, int mem_chunk_cnt)
 	ehdr->e_phoff = sizeof(Elf64_Ehdr);
 	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
 	ehdr->e_phentsize = sizeof(Elf64_Phdr);
-	/*
-	 * Number of memory chunk PT_LOAD program headers plus one kernel
-	 * image PT_LOAD program header plus one PT_NOTE program header.
-	 */
-	ehdr->e_phnum = mem_chunk_cnt + 1 + 1;
+	/* Number of PT_LOAD program headers plus PT_NOTE program header */
+	ehdr->e_phnum = phdr_count + 1;
 	return ehdr + 1;
 }
 
@@ -503,12 +500,14 @@ static int get_mem_chunk_cnt(void)
 /*
  * Initialize ELF loads (new kernel)
  */
-static void loads_init(Elf64_Phdr *phdr)
+static void loads_init(Elf64_Phdr *phdr, bool os_info_has_vm)
 {
-	unsigned long old_identity_base = os_info_old_value(OS_INFO_IDENTITY_BASE);
+	unsigned long old_identity_base = 0;
 	phys_addr_t start, end;
 	u64 idx;
 
+	if (os_info_has_vm)
+		old_identity_base = os_info_old_value(OS_INFO_IDENTITY_BASE);
 	for_each_physmem_range(idx, &oldmem_type, &start, &end) {
 		phdr->p_type = PT_LOAD;
 		phdr->p_vaddr = old_identity_base + start;
@@ -522,6 +521,11 @@ static void loads_init(Elf64_Phdr *phdr)
 	}
 }
 
+static bool os_info_has_vm(void)
+{
+	return os_info_old_value(OS_INFO_KASLR_OFFSET);
+}
+
 /*
  * Prepare PT_LOAD type program header for kernel image region
  */
@@ -566,7 +570,7 @@ static void *notes_init(Elf64_Phdr *phdr, void *ptr, u64 notes_offset)
 	return ptr;
 }
 
-static size_t get_elfcorehdr_size(int mem_chunk_cnt)
+static size_t get_elfcorehdr_size(int phdr_count)
 {
 	size_t size;
 
@@ -581,10 +585,8 @@ static size_t get_elfcorehdr_size(int mem_chunk_cnt)
 	size += nt_vmcoreinfo_size();
 	/* nt_final */
 	size += sizeof(Elf64_Nhdr);
-	/* PT_LOAD type program header for kernel text region */
-	size += sizeof(Elf64_Phdr);
 	/* PT_LOADS */
-	size += mem_chunk_cnt * sizeof(Elf64_Phdr);
+	size += phdr_count * sizeof(Elf64_Phdr);
 
 	return size;
 }
@@ -595,8 +597,8 @@ static size_t get_elfcorehdr_size(int mem_chunk_cnt)
 int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
 {
 	Elf64_Phdr *phdr_notes, *phdr_loads, *phdr_text;
+	int mem_chunk_cnt, phdr_text_cnt;
 	size_t alloc_size;
-	int mem_chunk_cnt;
 	void *ptr, *hdr;
 	u64 hdr_off;
 
@@ -615,34 +617,38 @@ int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size)
 	}
 
 	mem_chunk_cnt = get_mem_chunk_cnt();
+	phdr_text_cnt = os_info_has_vm() ? 1 : 0;
 
-	alloc_size = get_elfcorehdr_size(mem_chunk_cnt);
+	alloc_size = get_elfcorehdr_size(mem_chunk_cnt + phdr_text_cnt);
 
 	hdr = kzalloc(alloc_size, GFP_KERNEL);
 
-	/* Without elfcorehdr /proc/vmcore cannot be created. Thus creating
+	/*
+	 * Without elfcorehdr /proc/vmcore cannot be created. Thus creating
 	 * a dump with this crash kernel will fail. Panic now to allow other
 	 * dump mechanisms to take over.
 	 */
 	if (!hdr)
 		panic("s390 kdump allocating elfcorehdr failed");
 
 	/* Init elf header */
-	ptr = ehdr_init(hdr, mem_chunk_cnt);
+	phdr_notes = ehdr_init(hdr, mem_chunk_cnt + phdr_text_cnt);
 	/* Init program headers */
-	phdr_notes = ptr;
-	ptr = PTR_ADD(ptr, sizeof(Elf64_Phdr));
-	phdr_text = ptr;
-	ptr = PTR_ADD(ptr, sizeof(Elf64_Phdr));
-	phdr_loads = ptr;
-	ptr = PTR_ADD(ptr, sizeof(Elf64_Phdr) * mem_chunk_cnt);
+	if (phdr_text_cnt) {
+		phdr_text = phdr_notes + 1;
+		phdr_loads = phdr_text + 1;
+	} else {
+		phdr_loads = phdr_notes + 1;
+	}
+	ptr = PTR_ADD(phdr_loads, sizeof(Elf64_Phdr) * mem_chunk_cnt);
 	/* Init notes */
 	hdr_off = PTR_DIFF(ptr, hdr);
 	ptr = notes_init(phdr_notes, ptr, ((unsigned long) hdr) + hdr_off);
 	/* Init kernel text program header */
-	text_init(phdr_text);
+	if (phdr_text_cnt)
+		text_init(phdr_text);
 	/* Init loads */
-	loads_init(phdr_loads);
+	loads_init(phdr_loads, phdr_text_cnt);
 	/* Finalize program headers */
 	hdr_off = PTR_DIFF(ptr, hdr);
 	*addr = (unsigned long long) hdr;