Michael Schmitz <schmitzmic@xxxxxxxxx> writes:
> Multiple syscalls are liable to PTRACE_EVENT_* tracing and thus
> require full user context saved on the kernel stack. We only
> save those registers not preserved by C code currently.
>
> do_exit() calls ptrace_stop() which may require access to all
> saved registers. Add code to save additional registers in the
> switch_stack struct for exit and exit_group syscalls (similar
> to what is already done for fork, vfork and clone3). According
> to Eric's analysis, execve and execveat can be traced as well,
> so have been given the same treatment.
>
> I'm not sure what to do about io_uring_setup - added code to
> save full context on entry, and some more code to save/restore
> additional registers on the switch stack around the kworker thread
> call in ret_from_kernel_thread, but this may well be redundant.
>
> I'd need specific test cases to exercise io_uring_setup in
> particular, to see whether stack offsets for pt_regs and the
> switch stack have been messed up.
>
> Boot tested on ARAnym - earlier version including io_uring entry
> save also tested on real hardware unter heavy IO load.
Are the registers that SAVE_SWITCH_STACK saves on m68k caller saved
registers?
The fact that the registers are saved somewhere on the stack on alpha is
what forces the registers to be saved before calling exit and exec.
Eric
> CC: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> CC: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
> Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx>
>
> --
> Changes from v1:
>
> - added exec, execve and io_uring_setup syscalls
> - save extra registers around kworker thread calls
> ---
> arch/m68k/kernel/entry.S | 41 ++++++++++++++++++++++++++++++++++-
> arch/m68k/kernel/process.c | 39 +++++++++++++++++++++++++++++++++
> arch/m68k/kernel/syscalls/syscall.tbl | 10 ++++-----
> 3 files changed, 84 insertions(+), 6 deletions(-)
>
> diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
> index 9dd76fb..02bf2a1 100644
> --- a/arch/m68k/kernel/entry.S
> +++ b/arch/m68k/kernel/entry.S
> @@ -76,6 +76,41 @@ ENTRY(__sys_clone3)
> lea %sp@(28),%sp
> rts
>
> +ENTRY(__sys_exit)
> + SAVE_SWITCH_STACK
> + pea %sp@(SWITCH_STACK_SIZE)
> + jbsr m68k_exit
> + lea %sp@(28),%sp
> + rts
> +
> +ENTRY(__sys_exit_group)
> + SAVE_SWITCH_STACK
> + pea %sp@(SWITCH_STACK_SIZE)
> + jbsr m68k_exit_group
> + lea %sp@(28),%sp
> + rts
> +
> +ENTRY(__sys_execve)
> + SAVE_SWITCH_STACK
> + pea %sp@(SWITCH_STACK_SIZE)
> + jbsr m68k_execve
> + lea %sp@(28),%sp
> + rts
> +
> +ENTRY(__sys_execveat)
> + SAVE_SWITCH_STACK
> + pea %sp@(SWITCH_STACK_SIZE)
> + jbsr m68k_execveat
> + lea %sp@(28),%sp
> + rts
> +
> +ENTRY(__sys_io_uring_setup)
> + SAVE_SWITCH_STACK
> + pea %sp@(SWITCH_STACK_SIZE)
> + jbsr m68k_io_uring_setup
> + lea %sp@(28),%sp
> + rts
> +
> ENTRY(sys_sigreturn)
> SAVE_SWITCH_STACK
> movel %sp,%sp@- | switch_stack pointer
> @@ -123,9 +158,13 @@ ENTRY(ret_from_kernel_thread)
> | a3 contains the kernel thread payload, d7 - its argument
> movel %d1,%sp@-
> jsr schedule_tail
> - movel %d7,(%sp)
> + addql #4,%sp
> + | kernel threads can be traced!
> + SAVE_SWITCH_STACK
> + movel %d7,%sp@-
> jsr %a3@
> addql #4,%sp
> + RESTORE_SWITCH_STACK
> jra ret_from_exception
>
> #if defined(CONFIG_COLDFIRE) || !defined(CONFIG_MMU)
> diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
> index da83cc8..298ac99 100644
> --- a/arch/m68k/kernel/process.c
> +++ b/arch/m68k/kernel/process.c
> @@ -138,6 +138,45 @@ asmlinkage int m68k_clone3(struct pt_regs *regs)
> return sys_clone3((struct clone_args __user *)regs->d1, regs->d2);
> }
>
> +/*
> + * Because extra registers are saved on the stack after the sys_exit()
> + * arguments, this C wrapper extracts them from pt_regs * and then calls the
> + * generic sys_exit() implementation.
> + */
> +asmlinkage int m68k_exit(struct pt_regs *regs)
> +{
> + return sys_exit(regs->d1);
> +}
> +
> +/* Same for sys_exit_group ... */
> +asmlinkage int m68k_exit_group(struct pt_regs *regs)
> +{
> + return sys_exit_group(regs->d1);
> +}
> +
> +/* Same for sys_exit_group ... */
> +asmlinkage int m68k_execve(struct pt_regs *regs)
> +{
> + return sys_execve((const char __user *)regs->d1,
> + (const char __user *const __user*)regs->d2,
> + (const char __user *const __user*)regs->d3);
> +}
> +
> +/* Same for sys_exit_group ... */
> +asmlinkage int m68k_execveat(struct pt_regs *regs)
> +{
> + return sys_execveat(regs->d1, (const char __user *)regs->d2,
> + (const char __user *const __user*)regs->d3,
> + (const char __user *const __user*)regs->d4,
> + regs->d5);
> +}
> +
> +/* and for sys_io_uring_create */
> +asmlinkage int m68k_io_uring_setup(struct pt_regs *regs)
> +{
> + return sys_io_uring_setup(regs->d1,(struct io_uring_params __user *)regs->d2);
> +}
> +
> int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
> struct task_struct *p, unsigned long tls)
> {
> diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> index 0dd019d..4a1ba1d 100644
> --- a/arch/m68k/kernel/syscalls/syscall.tbl
> +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> @@ -8,7 +8,7 @@
> # The <abi> is always "common" for this file
> #
> 0 common restart_syscall sys_restart_syscall
> -1 common exit sys_exit
> +1 common exit __sys_exit
> 2 common fork __sys_fork
> 3 common read sys_read
> 4 common write sys_write
> @@ -18,7 +18,7 @@
> 8 common creat sys_creat
> 9 common link sys_link
> 10 common unlink sys_unlink
> -11 common execve sys_execve
> +11 common execve __sys_execve
> 12 common chdir sys_chdir
> 13 common time sys_time32
> 14 common mknod sys_mknod
> @@ -254,7 +254,7 @@
> 244 common io_submit sys_io_submit
> 245 common io_cancel sys_io_cancel
> 246 common fadvise64 sys_fadvise64
> -247 common exit_group sys_exit_group
> +247 common exit_group __sys_exit_group
> 248 common lookup_dcookie sys_lookup_dcookie
> 249 common epoll_create sys_epoll_create
> 250 common epoll_ctl sys_epoll_ctl
> @@ -362,7 +362,7 @@
> 352 common getrandom sys_getrandom
> 353 common memfd_create sys_memfd_create
> 354 common bpf sys_bpf
> -355 common execveat sys_execveat
> +355 common execveat __sys_execveat
> 356 common socket sys_socket
> 357 common socketpair sys_socketpair
> 358 common bind sys_bind
> @@ -424,7 +424,7 @@
> 422 common futex_time64 sys_futex
> 423 common sched_rr_get_interval_time64 sys_sched_rr_get_interval
> 424 common pidfd_send_signal sys_pidfd_send_signal
> -425 common io_uring_setup sys_io_uring_setup
> +425 common io_uring_setup __sys_io_uring_setup
> 426 common io_uring_enter sys_io_uring_enter
> 427 common io_uring_register sys_io_uring_register
> 428 common open_tree sys_open_tree
