On Fri, Aug 30, 2024 at 3:36 PM Noah Goldstein <goldstein....@gmail.com> wrote:
>
> The new option '-qemu-children' makes it so that on `execve` the child
> process will be launch by the same `qemu` executable that is currently
> running along with its current commandline arguments.
>
> The motivation for the change is to make it so that plugins running
> through `qemu` can continue to run on children. Why not just
> `binfmt`?: Plugins can be desirable regardless of system/architecture
> emulation, and can sometimes be useful for elf files that can run
> natively. Enabling `binfmt` for all natively runnable elf files may
> not be desirable.
>
> Signed-off-by: Noah Goldstein <goldstein....@gmail.com>
> ---
> linux-user/main.c | 22 ++++++++++++++++++++++
> linux-user/syscall.c | 20 +++++++++++++++-----
> linux-user/user-internals.h | 4 ++++
> 3 files changed, 41 insertions(+), 5 deletions(-)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 8143a0d4b0..dfb303a1f2 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -81,6 +81,10 @@ unsigned long mmap_min_addr;
> uintptr_t guest_base;
> bool have_guest_base;
>
> +bool qemu_dup_for_children;
> +int qemu_argc;
> +char ** qemu_argv;
> +
> /*
> * Used to implement backwards-compatibility for the `-strace`, and
> * QEMU_STRACE options. Without this, the QEMU_LOG can be overwritten by
> @@ -451,6 +455,11 @@ static void handle_arg_jitdump(const char *arg)
> perf_enable_jitdump();
> }
>
> +static void handle_arg_qemu_children(const char *arg)
> +{
> + qemu_dup_for_children = true;
> +}
> +
> static QemuPluginList plugins = QTAILQ_HEAD_INITIALIZER(plugins);
>
> #ifdef CONFIG_PLUGIN
> @@ -526,6 +535,10 @@ static const struct qemu_argument arg_table[] = {
> "", "Generate a /tmp/perf-${pid}.map file for perf"},
> {"jitdump", "QEMU_JITDUMP", false, handle_arg_jitdump,
> "", "Generate a jit-${pid}.dump file for perf"},
> + {"qemu-children",
> + "QEMU_CHILDREN", false, handle_arg_qemu_children,
> + "", "Run child processes (created with execve) with qemu "
> + "(as instantiated for the parent)"},
> {NULL, NULL, false, NULL, NULL, NULL}
> };
>
> @@ -729,6 +742,15 @@ int main(int argc, char **argv, char **envp)
>
> optind = parse_args(argc, argv);
>
> + if (qemu_dup_for_children) {
> + int i;
> + qemu_argc = optind;
> + qemu_argv = g_new0(char *, qemu_argc);
> + for (i = 0; i < optind; ++i) {
> + qemu_argv[i] = strdup(argv[i]);
> + }
> + }
> +
> qemu_set_log_filename_flags(last_log_filename,
> last_log_mask | (enable_strace * LOG_STRACE),
> &error_fatal);
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 9d5415674d..732ef89054 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -8459,13 +8459,14 @@ static int do_execv(CPUArchState *cpu_env, int dirfd,
> abi_long pathname, abi_long guest_argp,
> abi_long guest_envp, int flags, bool is_execveat)
> {
> - int ret;
> + int ret, argp_offset;
> char **argp, **envp;
> int argc, envc;
> abi_ulong gp;
> abi_ulong addr;
> char **q;
> void *p;
> + bool through_qemu = !is_execveat && qemu_dup_for_children;
>
I wasn't sure if this was feasible for `evecveat`. If anyone has any thoughts
it would be nice to support that as well.
> argc = 0;
>
> @@ -8489,10 +8490,11 @@ static int do_execv(CPUArchState *cpu_env, int dirfd,
> envc++;
> }
>
> - argp = g_new0(char *, argc + 1);
> + argp_offset = through_qemu ? qemu_argc : 0;
> + argp = g_new0(char *, argc + argp_offset + 1);
> envp = g_new0(char *, envc + 1);
>
> - for (gp = guest_argp, q = argp; gp; gp += sizeof(abi_ulong), q++) {
> + for (gp = guest_argp, q = argp + argp_offset; gp; gp +=
> sizeof(abi_ulong), q++) {
> if (get_user_ual(addr, gp)) {
> goto execve_efault;
> }
> @@ -8537,9 +8539,17 @@ static int do_execv(CPUArchState *cpu_env, int dirfd,
> }
>
> const char *exe = p;
> - if (is_proc_myself(p, "exe")) {
> + if (through_qemu) {
> + int i;
> + for (i = 0; i < argp_offset; ++i) {
> + argp[i] = qemu_argv[i];
> + }
> + exe = qemu_argv[0];
> + }
> + else if (is_proc_myself(p, "exe")) {
> exe = exec_path;
> }
> +
> ret = is_execveat
> ? safe_execveat(dirfd, exe, argp, envp, flags)
> : safe_execve(exe, argp, envp);
> @@ -8553,7 +8563,7 @@ execve_efault:
> ret = -TARGET_EFAULT;
>
> execve_end:
> - for (gp = guest_argp, q = argp; *q; gp += sizeof(abi_ulong), q++) {
> + for (gp = guest_argp, q = argp + argp_offset; *q; gp +=
> sizeof(abi_ulong), q++) {
> if (get_user_ual(addr, gp) || !addr) {
> break;
> }
> diff --git a/linux-user/user-internals.h b/linux-user/user-internals.h
> index 5c7f173ceb..0719e65ff4 100644
> --- a/linux-user/user-internals.h
> +++ b/linux-user/user-internals.h
> @@ -30,6 +30,10 @@ void stop_all_tasks(void);
> extern const char *qemu_uname_release;
> extern unsigned long mmap_min_addr;
>
> +extern bool qemu_dup_for_children;
> +extern int qemu_argc;
> +extern char ** qemu_argv;
> +
> typedef struct IOCTLEntry IOCTLEntry;
>
> typedef abi_long do_ioctl_fn(const IOCTLEntry *ie, uint8_t *buf_temp,
> --
> 2.34.1
>
