Re: [PATCH v3 07/13] task_isolation: arch/arm64: enable task isolation functionality

Catalin Marinas
2020-04-22T12:08:17Z

On Thu, Apr 09, 2020 at 03:23:35PM +0000, Alex Belits wrote:
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index f0cec4160136..7563098eb5b2 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -63,6 +63,7 @@ void arch_release_task_struct(struct task_struct *tsk);
> #define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */
> #define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */
> #define TIF_FSCHECK 5 /* Check FS is USER_DS on return */
> +#define TIF_TASK_ISOLATION 6
> #define TIF_NOHZ 7
> #define TIF_SYSCALL_TRACE 8 /* syscall trace active */
> #define TIF_SYSCALL_AUDIT 9 /* syscall auditing */
> @@ -83,6 +84,7 @@ void arch_release_task_struct(struct task_struct *tsk);
> #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
> #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
> #define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE)
> +#define _TIF_TASK_ISOLATION (1 << TIF_TASK_ISOLATION)
> #define _TIF_NOHZ (1 << TIF_NOHZ)
> #define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
> #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
> @@ -96,7 +98,8 @@ void arch_release_task_struct(struct task_struct *tsk);
>
> #define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
> _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
> - _TIF_UPROBE | _TIF_FSCHECK)
> + _TIF_UPROBE | _TIF_FSCHECK | \
> + _TIF_TASK_ISOLATION)
>
> #define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
> _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index cd6e5fa48b9c..b35b9b0c594c 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -29,6 +29,7 @@
> #include <linux/regset.h>
> #include <linux/tracehook.h>
> #include <linux/elf.h>
> +#include <linux/isolation.h>
>
> #include <asm/compat.h>
> #include <asm/cpufeature.h>
> @@ -1836,6 +1837,15 @@ int syscall_trace_enter(struct pt_regs *regs)
> return -1;
> }
>
> + /*
> + * In task isolation mode, we may prevent the syscall from
> + * running, and if so we also deliver a signal to the process.
> + */
> + if (test_thread_flag(TIF_TASK_ISOLATION)) {
> + if (task_isolation_syscall(regs->syscallno) == -1)
> + return -1;
> + }

Is this supposed to be called only when syscall tracing is enabled?
It only gets here if the task has any of the _TIF_SYSCALL_WORK flags.

> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index 339882db5a91..d488c91a4877 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -20,6 +20,7 @@
> #include <linux/tracehook.h>
> #include <linux/ratelimit.h>
> #include <linux/syscalls.h>
> +#include <linux/isolation.h>
>
> #include <asm/daifflags.h>
> #include <asm/debug-monitors.h>
> @@ -898,6 +899,11 @@ static void do_signal(struct pt_regs *regs)
> restore_saved_sigmask();
> }
>
> +#define NOTIFY_RESUME_LOOP_FLAGS \
> + (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
> + _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
> + _TIF_UPROBE | _TIF_FSCHECK)

AFAICT, that's just _TIF_WORK_MASK without _TIF_TASK_ISOLATION. I'd
rather not duplicate these, they are prone to get out of sync. You could
do something like:

#define NOTIFY_RESUME_LOOP_FLAGS (_TIF_WORK_MASK & ~_TIF_TASK_ISOLATION)

> +
> asmlinkage void do_notify_resume(struct pt_regs *regs,
> unsigned long thread_flags)
> {
> @@ -908,6 +914,8 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
> */
> trace_hardirqs_off();
>
> + task_isolation_check_run_cleanup();
> +
> do {
> /* Check valid user FS if needed */
> addr_limit_user_check();
> @@ -938,7 +946,10 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
>
> local_daif_mask();
> thread_flags = READ_ONCE(current_thread_info()->flags);
> - } while (thread_flags & _TIF_WORK_MASK);
> + } while (thread_flags & NOTIFY_RESUME_LOOP_FLAGS);
> +
> + if (thread_flags & _TIF_TASK_ISOLATION)
> + task_isolation_start();
> }
>
> unsigned long __ro_after_init signal_minsigstksz;

--
Catalin