On Fri, Feb 10 2023 at 02:25, Gregory Price wrote:
>
> As the ABI of these intercepted syscalls is unknown to Linux, these
> -syscalls are not instrumentable via ptrace or the syscall tracepoints.
> +syscalls are not instrumentable via ptrace or the syscall tracepoints,
> +however an interfaces to suspend, checkpoint, and restore syscall user
> +dispatch configuration has been added to ptrace to assist userland
> +checkpoint/restart software.
The above is incomprehensible word salad to me. Once the ptrace
functions are there then they can be used independent of CRIU, no?
> + * struct ptrace_sud_config - Per-task configuration for SUD
> + * @mode: One of PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF
> + * @selector: Tracee's user virtual address of SUD selector
> + * @offset: SUD exclusion area (virtual address)
> + * @len: Length of SUD exclusion area
> + *
> + * Used to get/set the syscall user dispatch configuration for tracee.
> + * process. Selector is optional (may be NULL), and if invalid will produce
> + * a SIGSEGV in the tracee upon first access.
> + *
> + * If mode is PR_SYS_DISPATCH_ON, syscall dispatch will be enabled. If
> + * PR_SYS_DISPATCH_OFF, syscall dispatch will be disabled and all other
> + * parameters must be 0. The value in *selector (if not null), also determines
> + * whether syscall dispatch will occur.
> + *
> + * The SUD Exclusion area described by offset/len is the virtual address space
> + * from which syscalls will not produce a user dispatch.
> + */
> +struct ptrace_sud_config {
> + __u64 mode;
> + __s8 *selector;
How is this correct for a 32bit ptracer running on a 64bit kernel? Aside
of not wiring up the compat syscall without any argumentation in the
changelog.
> --- a/kernel/entry/syscall_user_dispatch.c
> +++ b/kernel/entry/syscall_user_dispatch.c
This section:
> -int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
> - unsigned long len, char __user *selector)
> +static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned long mode,
> + unsigned long offset, unsigned long len,
> + char __user *selector)
> {
> switch (mode) {
> case PR_SYS_DISPATCH_OFF:
> @@ -94,15 +96,60 @@ int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
> return -EINVAL;
> }
>
> - current->syscall_dispatch.selector = selector;
> - current->syscall_dispatch.offset = offset;
> - current->syscall_dispatch.len = len;
> - current->syscall_dispatch.on_dispatch = false;
> + task->syscall_dispatch.selector = selector;
> + task->syscall_dispatch.offset = offset;
> + task->syscall_dispatch.len = len;
> + task->syscall_dispatch.on_dispatch = false;
>
> if (mode == PR_SYS_DISPATCH_ON)
> - set_syscall_work(SYSCALL_USER_DISPATCH);
> + set_task_syscall_work(task, SYSCALL_USER_DISPATCH);
> else
> - clear_syscall_work(SYSCALL_USER_DISPATCH);
> + clear_task_syscall_work(task, SYSCALL_USER_DISPATCH);
>
> return 0;
> }
> +
> +int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
> + unsigned long len, char __user *selector)
> +{
> + return task_set_syscall_user_dispatch(current, mode, offset, len, selector);
> +}
until here want's to be a seperate preparatory patch.
> +++ b/tools/testing/selftests/ptrace/get_set_sud.c
> + child = fork();
> + ASSERT_GE(child, 0);
> + if (child == 0) {
> + ASSERT_EQ(0, sys_ptrace(PTRACE_TRACEME, 0, 0, 0)) {
> + TH_LOG("PTRACE_TRACEME: %m");
> + }
> + kill(getpid(), SIGSTOP);
> + sleep(2);
The purpose of this sleep is what?
> + _exit(1);
> + }
> +
> + waitpid(child, &status, 0);
> +
> + config.mode = PR_SYS_DISPATCH_ON;
> + config.selector = (void*)0xDEADBEEF;
> + config.offset = 0x12345678;
> + config.len = 0x87654321;
What's the purpose of these magic numbers? memset(&config, 0xff,...) is
sufficient, no?
Thanks,
tglx
