linux-user: Do not clobber bprm_buf swapping ehdr

Rearrange the allocation of storage for ehdr between load_elf_image
and load_elf_binary.  The same set of copies are done, but we don't
modify bprm_buf, which will be important later.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/elfload.c

@@ -3199,16 +3199,17 @@ static bool parse_elf_properties(int image_fd,
    On return: INFO values will be filled in, as necessary or available.  */
 
 static void load_elf_image(const char *image_name, int image_fd,
-                           struct image_info *info, char **pinterp_name,
+                           struct image_info *info, struct elfhdr *ehdr,
+                           char **pinterp_name,
                            char bprm_buf[BPRM_BUF_SIZE])
 {
-    struct elfhdr *ehdr = (struct elfhdr *)bprm_buf;
     struct elf_phdr *phdr;
     abi_ulong load_addr, load_bias, loaddr, hiaddr, error;
     int i, retval, prot_exec;
     Error *err = NULL;
 
     /* First of all, some simple consistency checks */
+    memcpy(ehdr, bprm_buf, sizeof(*ehdr));
     if (!elf_check_ident(ehdr)) {
         error_setg(&err, "Invalid ELF image for this architecture");
         goto exit_errmsg;
@@ -3523,6 +3524,7 @@ static void load_elf_image(const char *image_name, int image_fd,
 static void load_elf_interp(const char *filename, struct image_info *info,
                             char bprm_buf[BPRM_BUF_SIZE])
 {
+    struct elfhdr ehdr;
     int fd, retval;
     Error *err = NULL;
 
@@ -3544,7 +3546,7 @@ static void load_elf_interp(const char *filename, struct image_info *info,
         memset(bprm_buf + retval, 0, BPRM_BUF_SIZE - retval);
     }
 
-    load_elf_image(filename, fd, info, NULL, bprm_buf);
+    load_elf_image(filename, fd, info, &ehdr, NULL, bprm_buf);
 }
 
 static int symfind(const void *s0, const void *s1)
@@ -3737,8 +3739,14 @@ uint32_t get_elf_eflags(int fd)
 
 int load_elf_binary(struct linux_binprm *bprm, struct image_info *info)
 {
+    /*
+     * We need a copy of the elf header for passing to create_elf_tables.
+     * We will have overwritten the original when we re-use bprm->buf
+     * while loading the interpreter.  Allocate the storage for this now
+     * and let elf_load_image do any swapping that may be required.
+     */
+    struct elfhdr ehdr;
     struct image_info interp_info;
-    struct elfhdr elf_ex;
     char *elf_interpreter = NULL;
     char *scratch;
 
@@ -3748,12 +3756,7 @@ int load_elf_binary(struct linux_binprm *bprm, struct image_info *info)
 #endif
 
     load_elf_image(bprm->filename, bprm->fd, info,
-                   &elf_interpreter, bprm->buf);
-
-    /* ??? We need a copy of the elf header for passing to create_elf_tables.
-       If we do nothing, we'll have overwritten this when we re-use bprm->buf
-       when we load the interpreter.  */
-    elf_ex = *(struct elfhdr *)bprm->buf;
+                   &ehdr, &elf_interpreter, bprm->buf);
 
     /* Do this so that we can load the interpreter, if need be.  We will
        change some of these later */
@@ -3840,7 +3843,7 @@ int load_elf_binary(struct linux_binprm *bprm, struct image_info *info)
         target_mprotect(tramp_page, TARGET_PAGE_SIZE, PROT_READ | PROT_EXEC);
     }
 
-    bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc, &elf_ex,
+    bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc, &ehdr,
                                 info, (elf_interpreter ? &interp_info : NULL));
     info->start_stack = bprm->p;