libelf-loader: introduce elf_load_image

Implement a new function, called elf_load_image, to perform the
actually copy of the elf image and clearing the padding.  The function
is implemented as memcpy and memset when the library is built as part
of the tools, but it is implemented as raw_copy_to_guest and
raw_clear_guest when built as part of Xen, so that it can be safely
called with an HVM style dom0.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>

tools/libxc/xc_dom_elfloader.c

@@ -310,9 +310,15 @@ static int xc_dom_parse_elf_kernel(struct xc_dom_image *dom)
 static int xc_dom_load_elf_kernel(struct xc_dom_image *dom)
 {
     struct elf_binary *elf = dom->private_loader;
+    int rc;
 
     elf->dest = xc_dom_seg_to_ptr(dom, &dom->kernel_seg);
-    elf_load_binary(elf);
+    rc = elf_load_binary(elf);
+    if ( rc < 0 )
+    {
+        DOMPRINTF("%s: failed to load elf binary", __FUNCTION__);
+        return rc;
+    }
     if ( dom->parms.bsd_symtab )
         xc_dom_load_elf_symtab(dom, elf, 1);
     return 0;

tools/libxc/xc_hvm_build.c

@@ -109,8 +109,9 @@ static int loadelfimage(
     elf->dest += elf->pstart & (PAGE_SIZE - 1);
 
     /* Load the initial elf image. */
-    elf_load_binary(elf);
-    rc = 0;
+    rc = elf_load_binary(elf);
+    if ( rc < 0 )
+        PERROR("Failed to load elf binary\n");
 
     munmap(elf->dest, pages << PAGE_SHIFT);
     elf->dest = NULL;

xen/arch/x86/domain_build.c

@@ -903,7 +903,12 @@ int __init construct_dom0(
 
     /* Copy the OS image and free temporary buffer. */
     elf.dest = (void*)vkern_start;
-    elf_load_binary(&elf);
+    rc = elf_load_binary(&elf);
+    if ( rc < 0 )
+    {
+        printk("Failed to load the kernel binary\n");
+        return rc;
+    }
     bootstrap_map(NULL);
 
     if ( UNSET_ADDR != parms.virt_hypercall )

xen/common/libelf/libelf-loader.c

@@ -107,11 +107,34 @@ void elf_set_log(struct elf_binary *elf, elf_log_callback *log_callback,
     elf->log_caller_data = log_caller_data;
     elf->verbose = verbose;
 }
+
+static int elf_load_image(void *dst, const void *src, uint64_t filesz, uint64_t memsz)
+{
+    memcpy(dst, src, filesz);
+    memset(dst + filesz, 0, memsz - filesz);
+    return 0;
+}
 #else
+#include <asm/guest_access.h>
+
 void elf_set_verbose(struct elf_binary *elf)
 {
     elf->verbose = 1;
 }
+
+static int elf_load_image(void *dst, const void *src, uint64_t filesz, uint64_t memsz)
+{
+    int rc;
+    if ( filesz > ULONG_MAX || memsz > ULONG_MAX )
+        return -1;
+    rc = raw_copy_to_guest(dst, src, filesz);
+    if ( rc != 0 )
+        return -1;
+    rc = raw_clear_guest(dst + filesz, memsz - filesz);
+    if ( rc != 0 )
+        return -1;
+    return 0;
+}
 #endif
 
 /* Calculate the required additional kernel space for the elf image */
@@ -237,7 +260,7 @@ void elf_parse_binary(struct elf_binary *elf)
             __FUNCTION__, elf->pstart, elf->pend);
 }
 
-void elf_load_binary(struct elf_binary *elf)
+int elf_load_binary(struct elf_binary *elf)
 {
     const elf_phdr *phdr;
     uint64_t i, count, paddr, offset, filesz, memsz;
@@ -256,11 +279,12 @@ void elf_load_binary(struct elf_binary *elf)
         dest = elf_get_ptr(elf, paddr);
         elf_msg(elf, "%s: phdr %" PRIu64 " at 0x%p -> 0x%p\n",
                 __func__, i, dest, dest + filesz);
-        memcpy(dest, elf->image + offset, filesz);
-        memset(dest + filesz, 0, memsz - filesz);
+        if ( elf_load_image(dest, elf->image + offset, filesz, memsz) != 0 )
+            return -1;
     }
 
     elf_load_bsdsyms(elf);
+    return 0;
 }
 
 void *elf_get_ptr(struct elf_binary *elf, unsigned long addr)

xen/include/xen/libelf.h

@@ -198,7 +198,7 @@ void elf_set_log(struct elf_binary *elf, elf_log_callback*,
 #endif
 
 void elf_parse_binary(struct elf_binary *elf);
-void elf_load_binary(struct elf_binary *elf);
+int elf_load_binary(struct elf_binary *elf);
 
 void *elf_get_ptr(struct elf_binary *elf, unsigned long addr);
 uint64_t elf_lookup_addr(struct elf_binary *elf, const char *symbol);