On Wed, Oct 30, 2024 at 9:10 AM 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 | 21 ++++++
> linux-user/syscall.c | 21 ++++--
> linux-user/user-internals.h | 4 ++
> tests/tcg/multiarch/Makefile.target | 8 +++
> .../linux/linux-execve-qemu-children.c | 68 +++++++++++++++++++
> 5 files changed, 117 insertions(+), 5 deletions(-)
> create mode 100644 tests/tcg/multiarch/linux/linux-execve-qemu-children.c
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 8143a0d4b0..5e3d41dc2b 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 +742,14 @@ int main(int argc, char **argv, char **envp)
>
> optind = parse_args(argc, argv);
>
> + if (qemu_dup_for_children) {
> + 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 59b2080b98..96b105e9ce 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -8550,13 +8550,14 @@ 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 = dirfd == AT_FDCWD && qemu_dup_for_children;
>
> argc = 0;
>
> @@ -8580,10 +8581,12 @@ 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;
> }
> @@ -8628,9 +8631,16 @@ 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);
> @@ -8644,7 +8654,8 @@ 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 46ffc093f4..ed3ed666a0 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,
> diff --git a/tests/tcg/multiarch/Makefile.target
> b/tests/tcg/multiarch/Makefile.target
> index 78b83d5575..0e220953e7 100644
> --- a/tests/tcg/multiarch/Makefile.target
> +++ b/tests/tcg/multiarch/Makefile.target
> @@ -30,6 +30,14 @@ run-float_%: float_%
> $(call
> conditional-diff-out,$<,$(SRC_PATH)/tests/tcg/$(TARGET_NAME)/$<.ref)
>
>
> +run-linux-execve-qemu-children: linux-execve-qemu-children
> + $(call run-test,$<, $(QEMU) $(QEMU_OPTS) -qemu-children $< $(QEMU) 0)
> + $(call run-test,$<, $(QEMU) $(QEMU_OPTS) $< linux-execve 0 skip)
> +
> +run-plugin-linux-execve-qemu-children-with-%: linux-execve-qemu-children
> + $(call run-test,$<, $(QEMU) $(QEMU_OPTS) -qemu-children $< $(QEMU) 0)
> + $(call run-test,$<, $(QEMU) $(QEMU_OPTS) $< linux-execve 0 skip)
> +
> testthread: LDFLAGS+=-lpthread
>
> threadcount: LDFLAGS+=-lpthread
> diff --git a/tests/tcg/multiarch/linux/linux-execve-qemu-children.c
> b/tests/tcg/multiarch/linux/linux-execve-qemu-children.c
> new file mode 100644
> index 0000000000..60d6537666
> --- /dev/null
> +++ b/tests/tcg/multiarch/linux/linux-execve-qemu-children.c
> @@ -0,0 +1,68 @@
> +#include <assert.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <libgen.h>
> +#include <malloc.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <unistd.h>
> +
> +#define MAX_COMM_SIZE (4096)
> +
> +int
> +main(int argc, char ** argv, char ** envp) {
> + int fd;
> + char next_arg[2];
> + char * buf;
> + ssize_t off;
> + const char * expec_comm;
> + assert(argc == 3 || argc == 4);
> + fd = open("/proc/self/comm", O_RDONLY);
> + assert(fd > 0);
> +
> + buf = calloc(MAX_COMM_SIZE + 1, 1);
> + assert(buf != NULL);
> +
> + off = 0;
> + for (;;) {
> + ssize_t res = read(fd, buf + off, 1);
> + if (res < 0 && errno != EAGAIN) {
> + perror("Failed to read comm");
> + return -1;
> + }
> + if (res == 0) {
> + break;
> + }
> +
> + off += res;
> +
> + if (off >= MAX_COMM_SIZE) {
> + fprintf(stderr, "/proc/self/comm too large for test\n");
> + return -1;
> + }
> + }
> + assert(off && buf[off] == '\0' && buf[off - 1] == '\n');
> + buf[off - 1] = '\0';
> + expec_comm = basename(argv[1]);
> + if (argc == 3 && strncmp(buf, expec_comm, strlen(expec_comm))) {
> + fprintf(stderr,
> + "Didn't propagate qemu settings\nComm: '%s'\nExpec: '%s'\n",
> + buf, expec_comm);
> + return -1;
> + }
> + free(buf);
> + next_arg[0] = argv[2][0];
> + next_arg[1] = '\0';
> + if (next_arg[0] == '9') {
> + return 0;
> + }
> + next_arg[0] += 1;
> + char * next_args[] = { argv[0], argv[1], next_arg, NULL };
> + int eres = execve(argv[0], &next_args[0], envp);
> + if (eres != 0) {
> + fprintf(stderr, "Unable to execve: %d/%d -> %s\n", eres, errno,
> + strerror(errno));
> + return -1;
> + }
> + return 0;
> +}
> --
> 2.43.0
>
Added test that tests both old behavior (no propagation of qemu)
and new behavior (propagation of qemu + cmdline).
Tested on Aarch64 + Linux with:
```
make check-tcg
```
