s390/kexec_file: Add ELF loader

Add an ELF loader for kexec_file. The main task here is to do proper sanity
checks on the ELF file. Basically all other functionality was already
implemented for the image loader.

Signed-off-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

4 files changed, 150 insertions, 0 deletions

diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
index 4c9da9974cf4..825dd0f7f221 100644
--- a/arch/s390/include/asm/kexec.h
+++ b/arch/s390/include/asm/kexec.h
@@ -67,5 +67,6 @@ int *kexec_file_update_kernel(struct kimage *iamge,
                               struct s390_load_data *data);
 
 extern const struct kexec_file_ops s390_kexec_image_ops;
+extern const struct kexec_file_ops s390_kexec_elf_ops;
 
 #endif /*_S390_KEXEC_H */
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index a84e9611c5c7..84ea6225efb4 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -83,6 +83,7 @@ obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
 obj-$(CONFIG_UPROBES)           += uprobes.o
 
 obj-$(CONFIG_KEXEC_FILE)        += machine_kexec_file.o kexec_image.o
+obj-$(CONFIG_KEXEC_FILE)        += kexec_elf.o
 
 obj-$(CONFIG_PERF_EVENTS)       += perf_event.o perf_cpum_cf.o perf_cpum_sf.o
 obj-$(CONFIG_PERF_EVENTS)       += perf_cpum_cf_events.o perf_regs.o
diff --git a/arch/s390/kernel/kexec_elf.c b/arch/s390/kernel/kexec_elf.c
new file mode 100644
index 000000000000..5a286b012043
--- /dev/null
+++ b/arch/s390/kernel/kexec_elf.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ELF loader for kexec_file_load system call.
+ *
+ * Copyright IBM Corp. 2018
+ *
+ * Author(s): Philipp Rudo <prudo@linux.vnet.ibm.com>
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/kexec.h>
+#include <asm/setup.h>
+
+static int kexec_file_add_elf_kernel(struct kimage *image,
+                                     struct s390_load_data *data,
+                                     char *kernel, unsigned long kernel_len)
+{
+        struct kexec_buf buf;
+        const Elf_Ehdr *ehdr;
+        const Elf_Phdr *phdr;
+        int i, ret;
+
+        ehdr = (Elf_Ehdr *)kernel;
+        buf.image = image;
+
+        phdr = (void *)ehdr + ehdr->e_phoff;
+        for (i = 0; i < ehdr->e_phnum; i++, phdr++) {
+                if (phdr->p_type != PT_LOAD)
+                        continue;
+
+                buf.buffer = kernel + phdr->p_offset;
+                buf.bufsz = phdr->p_filesz;
+
+                buf.mem = ALIGN(phdr->p_paddr, phdr->p_align);
+                buf.memsz = phdr->p_memsz;
+
+                if (phdr->p_paddr == 0) {
+                        data->kernel_buf = buf.buffer;
+                        data->memsz += STARTUP_NORMAL_OFFSET;
+
+                        buf.buffer += STARTUP_NORMAL_OFFSET;
+                        buf.bufsz -= STARTUP_NORMAL_OFFSET;
+
+                        buf.mem += STARTUP_NORMAL_OFFSET;
+                        buf.memsz -= STARTUP_NORMAL_OFFSET;
+                }
+
+                if (image->type == KEXEC_TYPE_CRASH)
+                        buf.mem += crashk_res.start;
+
+                ret = kexec_add_buffer(&buf);
+                if (ret)
+                        return ret;
+
+                data->memsz += buf.memsz;
+        }
+
+        return 0;
+}
+
+static void *s390_elf_load(struct kimage *image,
+                           char *kernel, unsigned long kernel_len,
+                           char *initrd, unsigned long initrd_len,
+                           char *cmdline, unsigned long cmdline_len)
+{
+        struct s390_load_data data = {0};
+        const Elf_Ehdr *ehdr;
+        const Elf_Phdr *phdr;
+        size_t size;
+        int i, ret;
+
+        /* image->fobs->probe already checked for valid ELF magic number. */
+        ehdr = (Elf_Ehdr *)kernel;
+
+        if (ehdr->e_type != ET_EXEC ||
+            ehdr->e_ident[EI_CLASS] != ELFCLASS64 ||
+            !elf_check_arch(ehdr))
+                return ERR_PTR(-EINVAL);
+
+        if (!ehdr->e_phnum || ehdr->e_phentsize != sizeof(Elf_Phdr))
+                return ERR_PTR(-EINVAL);
+
+        size = ehdr->e_ehsize + ehdr->e_phoff;
+        size += ehdr->e_phentsize * ehdr->e_phnum;
+        if (size > kernel_len)
+                return ERR_PTR(-EINVAL);
+
+        phdr = (void *)ehdr + ehdr->e_phoff;
+        size = ALIGN(size, phdr->p_align);
+        for (i = 0; i < ehdr->e_phnum; i++, phdr++) {
+                if (phdr->p_type == PT_INTERP)
+                        return ERR_PTR(-EINVAL);
+
+                if (phdr->p_offset > kernel_len)
+                        return ERR_PTR(-EINVAL);
+
+                size += ALIGN(phdr->p_filesz, phdr->p_align);
+        }
+
+        if (size > kernel_len)
+                return ERR_PTR(-EINVAL);
+
+        ret = kexec_file_add_elf_kernel(image, &data, kernel, kernel_len);
+        if (ret)
+                return ERR_PTR(ret);
+
+        if (!data.memsz)
+                return ERR_PTR(-EINVAL);
+
+        if (initrd) {
+                ret = kexec_file_add_initrd(image, &data, initrd, initrd_len);
+                if (ret)
+                        return ERR_PTR(ret);
+        }
+
+        ret = kexec_file_add_purgatory(image, &data);
+        if (ret)
+                return ERR_PTR(ret);
+
+        return kexec_file_update_kernel(image, &data);
+}
+
+static int s390_elf_probe(const char *buf, unsigned long len)
+{
+        const Elf_Ehdr *ehdr;
+
+        if (len < sizeof(Elf_Ehdr))
+                return -ENOEXEC;
+
+        ehdr = (Elf_Ehdr *)buf;
+
+        /* Only check the ELF magic number here and do proper validity check
+         * in the loader. Any check here that fails would send the erroneous
+         * ELF file to the image loader that does not care what it gets.
+         * (Most likely) causing behavior not intended by the user.
+         */
+        if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
+                return -ENOEXEC;
+
+        return 0;
+}
+
+const struct kexec_file_ops s390_kexec_elf_ops = {
+        .probe = s390_elf_probe,
+        .load = s390_elf_load,
+};
diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
index 75aea2c1d823..f413f57f8d20 100644
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -12,6 +12,7 @@
 #include <asm/setup.h>
 
 const struct kexec_file_ops * const kexec_file_loaders[] = {
+        &s390_kexec_elf_ops,
         &s390_kexec_image_ops,
         NULL,
 };