Le 18/01/2016 05:33, Petros Angelatos a écrit : > From: Petros Angelatos <petros...@resin.io> > > In order for one to use QEMU user mode emulation under a chroot, it is > required to use binfmt_misc. This can be avoided by QEMU never doing a > raw execve() to the host system. > > Introduce a new option, -execve=path, that sets the absolute path to the > QEMU interpreter and enables execve() interception. When a guest process > tries to call execve(), qemu_execve() is called instead. > > qemu_execve() will prepend the interpreter set with -execve, similar to > what binfmt_misc would do, and then pass the modified execve() to the > host. > > It is necessary to parse hashbang scripts in that function otherwise > the kernel will try to run the interpreter of a script without QEMU and > get an invalid exec format error. > > Signed-off-by: Petros Angelatos <petros...@resin.io> > --- > linux-user/main.c | 8 ++++ > linux-user/qemu.h | 1 + > linux-user/syscall.c | 111 > ++++++++++++++++++++++++++++++++++++++++++++++++++- > 3 files changed, 119 insertions(+), 1 deletion(-) > > diff --git a/linux-user/main.c b/linux-user/main.c > index ee12035..5951279 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -79,6 +79,7 @@ static void usage(int exitcode); > > static const char *interp_prefix = CONFIG_QEMU_INTERP_PREFIX; > const char *qemu_uname_release; > +const char *qemu_execve_path; > > /* XXX: on x86 MAP_GROWSDOWN only works if ESP <= address + 32, so > we allocate a bigger stack. Need a better solution, for example > @@ -3828,6 +3829,11 @@ static void handle_arg_guest_base(const char *arg) > have_guest_base = 1; > } > > +static void handle_arg_execve(const char *arg) > +{ > + qemu_execve_path = strdup(arg);
I think you can use the parameter just as an on/off switch and realpath(argv[0]) as qemu_execve_path. I don't see any reason to use other binary than the one in use. > +} > + > static void handle_arg_reserved_va(const char *arg) > { > char *p; > @@ -3913,6 +3919,8 @@ static const struct qemu_argument arg_table[] = { > "uname", "set qemu uname release string to 'uname'"}, > {"B", "QEMU_GUEST_BASE", true, handle_arg_guest_base, > "address", "set guest_base address to 'address'"}, > + {"execve", "QEMU_EXECVE", true, handle_arg_execve, > + "path", "use interpreter at 'path' when a process calls > execve()"}, > {"R", "QEMU_RESERVED_VA", true, handle_arg_reserved_va, > "size", "reserve 'size' bytes for guest virtual address space"}, > {"d", "QEMU_LOG", true, handle_arg_log, > diff --git a/linux-user/qemu.h b/linux-user/qemu.h > index bd90cc3..0d9b058 100644 > --- a/linux-user/qemu.h > +++ b/linux-user/qemu.h > @@ -140,6 +140,7 @@ void init_task_state(TaskState *ts); > void task_settid(TaskState *); > void stop_all_tasks(void); > extern const char *qemu_uname_release; > +extern const char *qemu_execve_path; > extern unsigned long mmap_min_addr; > > /* ??? See if we can avoid exposing so much of the loader internals. */ > diff --git a/linux-user/syscall.c b/linux-user/syscall.c > index 0cbace4..d0b5442 100644 > --- a/linux-user/syscall.c > +++ b/linux-user/syscall.c > @@ -5854,6 +5854,109 @@ static target_timer_t get_timer_id(abi_long arg) > return timerid; > } > > +#define BINPRM_BUF_SIZE 128 This is defined in <linux/binfmts.h> > +/* qemu_execve() Must return target values and target errnos. */ > +static abi_long qemu_execve(char *filename, char *argv[], > + char *envp[]) > +{ > + char *i_arg = NULL, *i_name = NULL; > + char **new_argp; > + int argc, fd, ret, i, offset = 3; > + char *cp; > + char buf[BINPRM_BUF_SIZE]; > + > + for (argc = 0; argv[argc] != NULL; argc++) { > + /* nothing */ ; > + } > + > + fd = open(filename, O_RDONLY); > + if (fd == -1) { > + return -ENOENT; return -errno; ? > + } > + > + ret = read(fd, buf, BINPRM_BUF_SIZE); > + if (ret == -1) { > + close(fd); > + return -ENOENT; return -errno; ? > + } > + > + close(fd); > + > + /* adapted from the kernel > + * > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_script.c > + */ > + if ((buf[0] == '#') && (buf[1] == '!')) { what happens if read() < 2 ? > + /* > + * This section does the #! interpretation. > + * Sorta complicated, but hopefully it will work. -TYT > + */ > + > + buf[BINPRM_BUF_SIZE - 1] = '\0'; > + cp = strchr(buf, '\n'); > + if (cp == NULL) { > + cp = buf+BINPRM_BUF_SIZE-1; > + } > + *cp = '\0'; > + while (cp > buf) { > + cp--; > + if ((*cp == ' ') || (*cp == '\t')) { > + *cp = '\0'; > + } else { > + break; > + } > + } > + for (cp = buf+2; (*cp == ' ') || (*cp == '\t'); cp++) { > + /* nothing */ ; > + } > + if (*cp == '\0') { > + return -ENOEXEC; /* No interpreter name found */ > + } > + i_name = cp; > + i_arg = NULL; > + for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++) { > + /* nothing */ ; > + } > + while ((*cp == ' ') || (*cp == '\t')) { > + *cp++ = '\0'; > + } > + if (*cp) { > + i_arg = cp; > + } > + > + if (i_arg) { > + offset = 5; > + } else { > + offset = 4; > + } > + } > + > + new_argp = alloca((argc + offset + 1) * sizeof(void *)); > + > + /* Copy the original arguments with offset */ > + for (i = 0; i < argc; i++) { > + new_argp[i + offset] = argv[i]; > + } > + > + new_argp[0] = strdup(qemu_execve_path); > + new_argp[1] = strdup("-0"); > + new_argp[offset] = filename; > + new_argp[argc + offset] = NULL; > + > + if (i_name) { > + new_argp[2] = i_name; > + new_argp[3] = i_name; > + > + if (i_arg) { > + new_argp[4] = i_arg; > + } > + } else { > + new_argp[2] = argv[0]; > + } > + > + return get_errno(execve(qemu_execve_path, new_argp, envp)); duplicate get_errno() with the caller. > +} > + > /* do_syscall() should always have a single exit point at the end so > that actions, such as logging of syscall results, can be performed. > All errnos that do_syscall() returns must be -TARGET_<errcode>. */ > @@ -6113,7 +6216,13 @@ abi_long do_syscall(void *cpu_env, int num, abi_long > arg1, > > if (!(p = lock_user_string(arg1))) > goto execve_efault; > - ret = get_errno(execve(p, argp, envp)); > + > + if (qemu_execve_path && *qemu_execve_path) { > + ret = get_errno(qemu_execve(p, argp, envp)); > + } else { > + ret = get_errno(execve(p, argp, envp)); > + } > + what do you think of: ret = qemu_execve(p, argp, envp); and in qemu_execve(): if (qemu_execve_path == NULL || *qemu_execve_path == 0) { return get_errno(execve(p, argp, envp)); } so all the logic is in the function. > unlock_user(p, arg1, 0); > > goto execve_end; >