[Qemu-devel] [PATCH] Introduce option -binfmt-misc-friendly

["Kirill A. Shutemov" <kirill@shutemov.name>]

-binfmt-misc-friendly makes qemu compatible with binfmt_misc's flags 'P'
and 'O'.

'P' - preserve-argv[0].  Legacy behavior of binfmt_misc is to overwrite the
      original argv[0] with the full path to the binary.  When this flag is
      included, binfmt_misc will add an argument to the argument vector for
      this purpose, thus preserving the original argv[0].

'O' - open-binary. Legacy behavior of binfmt_misc is to pass the full path
      of the binary to the interpreter as an argument. When this flag is
      included, binfmt_misc will open the file for reading and pass its
      descriptor as an argument, instead of the full path, thus allowing
      the interpreter to execute non-readable binaries.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 linux-user/linuxload.c |    7 +----
 linux-user/main.c      |   54 ++++++++++++++++++++++++++++++++++++++++-------
 linux-user/qemu.h      |    2 +-
 3 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/linux-user/linuxload.c b/linux-user/linuxload.c
index ada7c69..cbd90f7 100644
--- a/linux-user/linuxload.c
+++ b/linux-user/linuxload.c
@@ -154,7 +154,7 @@ abi_ulong loader_build_argptr(int envc, int argc, abi_ulong sp,
     return sp;
 }
 
-int loader_exec(const char * filename, char ** argv, char ** envp,
+int loader_exec(int fd, const char * filename, char ** argv, char ** envp,
              struct target_pt_regs * regs, struct image_info *infop)
 {
     struct linux_binprm bprm;
@@ -164,10 +164,7 @@ int loader_exec(const char * filename, char ** argv, char ** envp,
     bprm.p = TARGET_PAGE_SIZE*MAX_ARG_PAGES-sizeof(unsigned int);
     for (i=0 ; i<MAX_ARG_PAGES ; i++)       /* clear page-table */
             bprm.page[i] = 0;
-    retval = open(filename, O_RDONLY);
-    if (retval < 0)
-        return retval;
-    bprm.fd = retval;
+    bprm.fd = fd;
     bprm.filename = (char *)filename;
     bprm.argc = count(argv);
     bprm.argv = argv;
diff --git a/linux-user/main.c b/linux-user/main.c
index 4bf739e..d3223f2 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -26,6 +26,7 @@
 
 #include "qemu.h"
 #include "qemu-common.h"
+#include "elf.h"
 /* For tb_lock */
 #include "exec-all.h"
 
@@ -2180,12 +2181,13 @@ static void usage(void)
            "Linux CPU emulator (compiled for %s emulation)\n"
            "\n"
            "Standard options:\n"
-           "-h                print this help\n"
-           "-g port           wait gdb connection to port\n"
-           "-L path           set the elf interpreter prefix (default=%s)\n"
-           "-s size           set the stack size in bytes (default=%ld)\n"
-           "-cpu model        select CPU (-cpu ? for list)\n"
-           "-drop-ld-preload  drop LD_PRELOAD for target process\n"
+           "-h                     print this help\n"
+           "-g port                wait gdb connection to port\n"
+           "-L path                set the elf interpreter prefix (default=%s)\n"
+           "-s size                set the stack size in bytes (default=%ld)\n"
+           "-cpu model             select CPU (-cpu ? for list)\n"
+           "-drop-ld-preload       drop LD_PRELOAD for target process\n"
+           "-binfmt-misc-friendly  make qemu compatible with binfmt_misc's flags 'O' and 'P' \n"
            "\n"
            "Debug options:\n"
            "-d options   activate log (logfile=%s)\n"
@@ -2218,9 +2220,10 @@ void init_task_state(TaskState *ts)
     ts->sigqueue_table[i].next = NULL;
 }
  
-int main(int argc, char **argv)
+int main(int argc, char **argv, char **envp)
 {
     const char *filename;
+    int fd = -1;
     const char *cpu_model;
     struct target_pt_regs regs1, *regs = &regs1;
     struct image_info info1, *info = &info1;
@@ -2230,6 +2233,7 @@ int main(int argc, char **argv)
     const char *r;
     int gdbstub_port = 0;
     int drop_ld_preload = 0, environ_count = 0;
+    int binfmt_misc_friendly = 0;
     char **target_environ, **wrk, **dst;
 
     if (argc <= 1)
@@ -2302,6 +2306,8 @@ int main(int argc, char **argv)
             drop_ld_preload = 1;
         } else if (!strcmp(r, "strace")) {
             do_strace = 1;
+        } else if (!strcmp(r, "binfmt-misc-friendly")) {
+	    binfmt_misc_friendly = 1;
         } else
         {
             usage();
@@ -2381,7 +2387,39 @@ int main(int argc, char **argv)
     }
     *dst = NULL; /* NULL terminate target_environ */
 
-    if (loader_exec(filename, argv+optind, target_environ, regs, info) != 0) {
+    if (binfmt_misc_friendly) {
+#if HOST_LONG_BITS == 32
+#define Elf_Dyn Elf32_Dyn
+#else
+#define Elf_Dyn Elf64_Dyn
+#endif
+	Elf_Dyn *auxv;
+
+	optind++; /* Handle binfmt_misc's option 'P' */
+
+	/* Handle binfmt_misc's option 'O' */
+	while(*envp++ != NULL); /* skip envp. we are on auxv now */
+	for(auxv = (Elf_Dyn *)envp; auxv->d_tag != AT_NULL; auxv++) {
+	    if( auxv->d_tag == AT_EXECFD) {
+		fd = auxv->d_un.d_val;
+		break;
+	    }
+	}
+
+	if (fd < 0) {
+	    printf("Cannot find binary file descriptor\n");
+	    _exit(1);
+	}
+
+    } else {
+	fd = open(filename, O_RDONLY);
+	if (fd < 0) {
+	    printf("Cannot open file %s: %s\n", filename, strerror(errno));
+	    _exit(1);
+	}
+    }
+
+    if (loader_exec(fd, filename, argv+optind, target_environ, regs, info) != 0) {
         printf("Error loading %s\n", filename);
         _exit(1);
     }
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index a12cc9b..216e2f8 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -168,7 +168,7 @@ struct linux_binprm {
 void do_init_thread(struct target_pt_regs *regs, struct image_info *infop);
 abi_ulong loader_build_argptr(int envc, int argc, abi_ulong sp,
                               abi_ulong stringp, int push_ptr);
-int loader_exec(const char * filename, char ** argv, char ** envp,
+int loader_exec(int fd, const char * filename, char ** argv, char ** envp,
              struct target_pt_regs * regs, struct image_info *infop);
 
 int load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
-- 
1.5.6.5.GIT