Re: [PATCH 06/12] task_isolation: arch/arm64: enable task isolation functionality

[Mark Rutland]

Hi Alex,

For patches affecting arm64, please CC LAKML and the arm64 maintainers
(Will and Catalin). I've Cc'd the maintainers here.

On Wed, Mar 04, 2020 at 04:10:28PM +0000, Alex Belits wrote:
> From: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
> 
> In do_notify_resume(), call task_isolation_start() for
> TIF_TASK_ISOLATION tasks. Add _TIF_TASK_ISOLATION to _TIF_WORK_MASK,
> and define a local NOTIFY_RESUME_LOOP_FLAGS to check in the loop,
> since we don't clear _TIF_TASK_ISOLATION in the loop.
> 
> We tweak syscall_trace_enter() slightly to carry the "flags"
> value from current_thread_info()->flags for each of the tests,
> rather than doing a volatile read from memory for each one. This
> avoids a small overhead for each test, and in particular avoids
> that overhead for TIF_NOHZ when TASK_ISOLATION is not enabled.

Stale commit message?

Looking at the patch below, this doesn't seem to be the case; it just
calls test_thread_flag(TIF_TASK_ISOLATION).

> 
> We instrument the smp_send_reschedule() routine so that it checks for
> isolated tasks and generates a suitable warning if needed.
> 
> Finally, report on page faults in task-isolation processes in
> do_page_faults().
> 
> Signed-off-by: Alex Belits <abelits@xxxxxxxxxxx>

The From line says this was from Chris Metcalf, but he's missing from
the Sign-off chain here, which isn't right.

> ---
>  arch/arm64/Kconfig                   |  1 +
>  arch/arm64/include/asm/thread_info.h |  5 ++++-
>  arch/arm64/kernel/ptrace.c           | 10 ++++++++++
>  arch/arm64/kernel/signal.c           | 13 ++++++++++++-
>  arch/arm64/kernel/smp.c              |  7 +++++++
>  arch/arm64/mm/fault.c                |  5 +++++
>  6 files changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 0b30e884e088..93b6aabc8be9 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -129,6 +129,7 @@ config ARM64
>  	select HAVE_ARCH_PREL32_RELOCATIONS
>  	select HAVE_ARCH_SECCOMP_FILTER
>  	select HAVE_ARCH_STACKLEAK
> +	select HAVE_ARCH_TASK_ISOLATION
>  	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
>  	select HAVE_ARCH_TRACEHOOK
>  	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
> 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;
> +	}

As above, this doesn't match the commit message.

AFAICT, task_isolation_syscall() always returns either 0 or -1, which
isn't great as an API. I see secure_computing() seems to do the same,
and it'd be nice to clean that up to either be a real erro code or a
boolean.

> +
>  	/* Do the secure computing after ptrace; failures should be fast. */
>  	if (secure_computing() == -1)
>  		return -1;
> 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)
> +
>  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;
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index d4ed9a19d8fe..00f0f77adea0 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -32,6 +32,7 @@
>  #include <linux/irq_work.h>
>  #include <linux/kexec.h>
>  #include <linux/kvm_host.h>
> +#include <linux/isolation.h>
>  
>  #include <asm/alternative.h>
>  #include <asm/atomic.h>
> @@ -818,6 +819,7 @@ void arch_send_call_function_single_ipi(int cpu)
>  #ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
>  void arch_send_wakeup_ipi_mask(const struct cpumask *mask)
>  {
> +	task_isolation_remote_cpumask(mask, "wakeup IPI");
>  	smp_cross_call(mask, IPI_WAKEUP);
>  }
>  #endif
> @@ -886,6 +888,9 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>  		__inc_irq_stat(cpu, ipi_irqs[ipinr]);
>  	}
>  
> +	task_isolation_interrupt("IPI type %d (%s)", ipinr,
> +				 ipinr < NR_IPI ? ipi_types[ipinr] : "unknown");
> +

Are these tracing hooks?

Surely they aren't necessary for functional correctness?

>  	switch (ipinr) {
>  	case IPI_RESCHEDULE:
>  		scheduler_ipi();
> @@ -948,12 +953,14 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>  
>  void smp_send_reschedule(int cpu)
>  {
> +	task_isolation_remote(cpu, "reschedule IPI");
>  	smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
>  }
>  
>  #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
>  void tick_broadcast(const struct cpumask *mask)
>  {
> +	task_isolation_remote_cpumask(mask, "timer IPI");
>  	smp_cross_call(mask, IPI_TIMER);
>  }
>  #endif
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 85566d32958f..fc4b42c81c4f 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -23,6 +23,7 @@
>  #include <linux/perf_event.h>
>  #include <linux/preempt.h>
>  #include <linux/hugetlb.h>
> +#include <linux/isolation.h>
>  
>  #include <asm/acpi.h>
>  #include <asm/bug.h>
> @@ -543,6 +544,10 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
>  	 */
>  	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
>  			      VM_FAULT_BADACCESS)))) {
> +		/* No signal was generated, but notify task-isolation tasks. */
> +		if (user_mode(regs))
> +			task_isolation_interrupt("page fault at %#lx", addr);
> +

We check user_mode(regs) much earlier in this function to set
FAULT_FLAG_USER. Is there some reason this cannot live there?

Also, this seems to be a tracing hook -- is this necessary?

Thanks,
Mark.

>  		/*
>  		 * Major/minor page fault accounting is only done
>  		 * once. If we go through a retry, it is extremely
> -- 
> 2.20.1
>