On Wed, Jan 18, 2023 at 03:10:53PM -0500, Gregory Price wrote:
> Adds PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH to ptrace options, and
> modify Syscall User Dispatch to suspend interception when enabled.
>
> This is modeled after the SUSPEND_SECCOMP feature, which suspends
> SECCOMP interposition. Without doing this, software like CRIU will
> inject system calls into a process and be intercepted by Syscall
> User Dispatch, either causing a crash (due to blocked signals) or
> the delivery of those signals to a ptracer (not the intended behavior).
>
> Since Syscall User Dispatch is not a privileged feature, a check
> for permissions is not required, however attempting to set this
> option when CONFIG_CHECKPOINT_RESTORE it not supported should be
> disallowed, as its intended use is checkpoint/resume.
>
> Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
One small nit -- see below, otherwise:
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
> include/linux/ptrace.h | 2 ++
> include/uapi/linux/ptrace.h | 6 +++++-
> kernel/entry/syscall_user_dispatch.c | 5 +++++
> kernel/ptrace.c | 5 +++++
> 4 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> index eaaef3ffec22..461ae5c99d57 100644
> --- a/include/linux/ptrace.h
> +++ b/include/linux/ptrace.h
> @@ -45,6 +45,8 @@ extern int ptrace_access_vm(struct task_struct *tsk, unsigned long addr,
>
> #define PT_EXITKILL (PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT)
> #define PT_SUSPEND_SECCOMP (PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT)
> +#define PT_SUSPEND_SYSCALL_USER_DISPATCH \
> + (PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH << PT_OPT_FLAG_SHIFT)
>
> extern long arch_ptrace(struct task_struct *child, long request,
> unsigned long addr, unsigned long data);
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index 195ae64a8c87..ba9e3f19a22c 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -146,9 +146,13 @@ struct ptrace_rseq_configuration {
> /* eventless options */
> #define PTRACE_O_EXITKILL (1 << 20)
> #define PTRACE_O_SUSPEND_SECCOMP (1 << 21)
> +#define PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH (1 << 22)
>
> #define PTRACE_O_MASK (\
> - 0x000000ff | PTRACE_O_EXITKILL | PTRACE_O_SUSPEND_SECCOMP)
> + 0x000000ff | \
> + PTRACE_O_EXITKILL | \
> + PTRACE_O_SUSPEND_SECCOMP | \
> + PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH)
>
> #include <asm/ptrace.h>
>
> diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c
> index 0b6379adff6b..7607f4598dd8 100644
> --- a/kernel/entry/syscall_user_dispatch.c
> +++ b/kernel/entry/syscall_user_dispatch.c
> @@ -8,6 +8,7 @@
> #include <linux/uaccess.h>
> #include <linux/signal.h>
> #include <linux/elf.h>
> +#include <linux/ptrace.h>
>
> #include <linux/sched/signal.h>
> #include <linux/sched/task_stack.h>
> @@ -36,6 +37,10 @@ bool syscall_user_dispatch(struct pt_regs *regs)
> struct syscall_user_dispatch *sd = ¤t->syscall_dispatch;
> char state;
>
> + if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) &&
> + unlikely(current->ptrace & PT_SUSPEND_SYSCALL_USER_DISPATCH))
Align with the '(' pleaase.
> + return false;
> +
> if (likely(instruction_pointer(regs) - sd->offset < sd->len))
> return false;
>
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 54482193e1ed..a6ad815bd4be 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -370,6 +370,11 @@ static int check_ptrace_options(unsigned long data)
> if (data & ~(unsigned long)PTRACE_O_MASK)
> return -EINVAL;
>
> + if (unlikely(data & PTRACE_O_SUSPEND_SYSCALL_USER_DISPATCH)) {
> + if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTART))
> + return -EINVAL;
> + }
> +
> if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
> if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
> !IS_ENABLED(CONFIG_SECCOMP))
> --
> 2.39.0
>
