Subject: Re: [PATCH v2] riscv: add support for SECCOMP and SECCOMP_FILTER

From: Kees Cook <[email-masked]>
Date: Tue, 15 Oct 2019 09:27:39 -0700

On Mon, Oct 14, 2019 at 02:06:07PM -0700, Paul Walmsley wrote:
> Shuah,
> 
> Could you please take a quick look at this and ack it if you're OK with 
> the tools/testing change?  We'd like to get this merged soon.

FWIW, I regularly carry these kinds of selftest changes via my seccomp
tree, so if Shuah is busy, I think it'll be fine to take this in
riscv. If not, I'll take responsibility of apologizing to Shuah! :) :)

-Kees

> 
> - Paul
> 
> 
> On Fri, 4 Oct 2019, Paul Walmsley wrote:
> 
> > Hello Shuah,
> > 
> > On Thu, 22 Aug 2019, David Abdurachmanov wrote:
> > 
> > > This patch was extensively tested on Fedora/RISCV (applied by default on
> > > top of 5.2-rc7 kernel for <2 months). The patch was also tested with 5.3-rc
> > > on QEMU and SiFive Unleashed board.
> > > 
> > > libseccomp (userspace) was rebased:
> > > https://github.com/seccomp/libseccomp/pull/134
> > > 
> > > Fully passes libseccomp regression testing (simulation and live).
> > > 
> > > There is one failing kernel selftest: global.user_notification_signal
> > > 
> > > v1 -> v2:
> > >   - return immediatly if secure_computing(NULL) returns -1
> > >   - fixed whitespace issues
> > >   - add missing seccomp.h
> > >   - remove patch #2 (solved now)
> > >   - add riscv to seccomp kernel selftest
> > > 
> > > Cc: [email-masked]
> > > Cc: [email-masked]
> > > 
> > > Signed-off-by: David Abdurachmanov <[email-masked]>
> > 
> > We'd like to merge this patch through the RISC-V tree.
> > Care to ack the change to tools/testing/selftests/seccomp/seccomp_bpf.c ?  
> > 
> > Kees has already reviewed it:
> > 
> > https://lore.kernel.org/linux-riscv/CAJr-aD=UnCN9E_mdVJ2H5nt=[email-masked]/
> > 
> > 
> > - Paul
> > 
> > 
> > > ---
> > >  arch/riscv/Kconfig                            | 14 ++++++++++
> > >  arch/riscv/include/asm/seccomp.h              | 10 +++++++
> > >  arch/riscv/include/asm/thread_info.h          |  5 +++-
> > >  arch/riscv/kernel/entry.S                     | 27 +++++++++++++++++--
> > >  arch/riscv/kernel/ptrace.c                    | 10 +++++++
> > >  tools/testing/selftests/seccomp/seccomp_bpf.c |  8 +++++-
> > >  6 files changed, 70 insertions(+), 4 deletions(-)
> > >  create mode 100644 arch/riscv/include/asm/seccomp.h
> > > 
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index 59a4727ecd6c..441e63ff5adc 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -31,6 +31,7 @@ config RISCV
> > >  	select GENERIC_SMP_IDLE_THREAD
> > >  	select GENERIC_ATOMIC64 if !64BIT
> > >  	select HAVE_ARCH_AUDITSYSCALL
> > > +	select HAVE_ARCH_SECCOMP_FILTER
> > >  	select HAVE_MEMBLOCK_NODE_MAP
> > >  	select HAVE_DMA_CONTIGUOUS
> > >  	select HAVE_FUTEX_CMPXCHG if FUTEX
> > > @@ -235,6 +236,19 @@ menu "Kernel features"
> > >  
> > >  source "kernel/Kconfig.hz"
> > >  
> > > +config SECCOMP
> > > +	bool "Enable seccomp to safely compute untrusted bytecode"
> > > +	help
> > > +	  This kernel feature is useful for number crunching applications
> > > +	  that may need to compute untrusted bytecode during their
> > > +	  execution. By using pipes or other transports made available to
> > > +	  the process as file descriptors supporting the read/write
> > > +	  syscalls, it's possible to isolate those applications in
> > > +	  their own address space using seccomp. Once seccomp is
> > > +	  enabled via prctl(PR_SET_SECCOMP), it cannot be disabled
> > > +	  and the task is only allowed to execute a few safe syscalls
> > > +	  defined by each seccomp mode.
> > > +
> > >  endmenu
> > >  
> > >  menu "Boot options"
> > > diff --git a/arch/riscv/include/asm/seccomp.h b/arch/riscv/include/asm/seccomp.h
> > > new file mode 100644
> > > index 000000000000..bf7744ee3b3d
> > > --- /dev/null
> > > +++ b/arch/riscv/include/asm/seccomp.h
> > > @@ -0,0 +1,10 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +
> > > +#ifndef _ASM_SECCOMP_H
> > > +#define _ASM_SECCOMP_H
> > > +
> > > +#include <asm/unistd.h>
> > > +
> > > +#include <asm-generic/seccomp.h>
> > > +
> > > +#endif /* _ASM_SECCOMP_H */
> > > diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> > > index 905372d7eeb8..a0b2a29a0da1 100644
> > > --- a/arch/riscv/include/asm/thread_info.h
> > > +++ b/arch/riscv/include/asm/thread_info.h
> > > @@ -75,6 +75,7 @@ struct thread_info {
> > >  #define TIF_MEMDIE		5	/* is terminating due to OOM killer */
> > >  #define TIF_SYSCALL_TRACEPOINT  6       /* syscall tracepoint instrumentation */
> > >  #define TIF_SYSCALL_AUDIT	7	/* syscall auditing */
> > > +#define TIF_SECCOMP		8	/* syscall secure computing */
> > >  
> > >  #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
> > >  #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
> > > @@ -82,11 +83,13 @@ struct thread_info {
> > >  #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
> > >  #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
> > >  #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
> > > +#define _TIF_SECCOMP		(1 << TIF_SECCOMP)
> > >  
> > >  #define _TIF_WORK_MASK \
> > >  	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED)
> > >  
> > >  #define _TIF_SYSCALL_WORK \
> > > -	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_AUDIT)
> > > +	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_AUDIT | \
> > > +	 _TIF_SECCOMP )
> > >  
> > >  #endif /* _ASM_RISCV_THREAD_INFO_H */
> > > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > > index bc7a56e1ca6f..0bbedfa3e47d 100644
> > > --- a/arch/riscv/kernel/entry.S
> > > +++ b/arch/riscv/kernel/entry.S
> > > @@ -203,8 +203,25 @@ check_syscall_nr:
> > >  	/* Check to make sure we don't jump to a bogus syscall number. */
> > >  	li t0, __NR_syscalls
> > >  	la s0, sys_ni_syscall
> > > -	/* Syscall number held in a7 */
> > > -	bgeu a7, t0, 1f
> > > +	/*
> > > +	 * The tracer can change syscall number to valid/invalid value.
> > > +	 * We use syscall_set_nr helper in syscall_trace_enter thus we
> > > +	 * cannot trust the current value in a7 and have to reload from
> > > +	 * the current task pt_regs.
> > > +	 */
> > > +	REG_L a7, PT_A7(sp)
> > > +	/*
> > > +	 * Syscall number held in a7.
> > > +	 * If syscall number is above allowed value, redirect to ni_syscall.
> > > +	 */
> > > +	bge a7, t0, 1f
> > > +	/*
> > > +	 * Check if syscall is rejected by tracer or seccomp, i.e., a7 == -1.
> > > +	 * If yes, we pretend it was executed.
> > > +	 */
> > > +	li t1, -1
> > > +	beq a7, t1, ret_from_syscall_rejected
> > > +	/* Call syscall */
> > >  	la s0, sys_call_table
> > >  	slli t0, a7, RISCV_LGPTR
> > >  	add s0, s0, t0
> > > @@ -215,6 +232,12 @@ check_syscall_nr:
> > >  ret_from_syscall:
> > >  	/* Set user a0 to kernel a0 */
> > >  	REG_S a0, PT_A0(sp)
> > > +	/*
> > > +	 * We didn't execute the actual syscall.
> > > +	 * Seccomp already set return value for the current task pt_regs.
> > > +	 * (If it was configured with SECCOMP_RET_ERRNO/TRACE)
> > > +	 */
> > > +ret_from_syscall_rejected:
> > >  	/* Trace syscalls, but only if requested by the user. */
> > >  	REG_L t0, TASK_TI_FLAGS(tp)
> > >  	andi t0, t0, _TIF_SYSCALL_WORK
> > > diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
> > > index 368751438366..63e47c9f85f0 100644
> > > --- a/arch/riscv/kernel/ptrace.c
> > > +++ b/arch/riscv/kernel/ptrace.c
> > > @@ -154,6 +154,16 @@ void do_syscall_trace_enter(struct pt_regs *regs)
> > >  		if (tracehook_report_syscall_entry(regs))
> > >  			syscall_set_nr(current, regs, -1);
> > >  
> > > +	/*
> > > +	 * Do the secure computing after ptrace; failures should be fast.
> > > +	 * If this fails we might have return value in a0 from seccomp
> > > +	 * (via SECCOMP_RET_ERRNO/TRACE).
> > > +	 */
> > > +	if (secure_computing(NULL) == -1) {
> > > +		syscall_set_nr(current, regs, -1);
> > > +		return;
> > > +	}
> > > +
> > >  #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
> > >  	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
> > >  		trace_sys_enter(regs, syscall_get_nr(current, regs));
> > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> > > index 6ef7f16c4cf5..492e0adad9d3 100644
> > > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> > > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> > > @@ -112,6 +112,8 @@ struct seccomp_data {
> > >  #  define __NR_seccomp 383
> > >  # elif defined(__aarch64__)
> > >  #  define __NR_seccomp 277
> > > +# elif defined(__riscv)
> > > +#  define __NR_seccomp 277
> > >  # elif defined(__hppa__)
> > >  #  define __NR_seccomp 338
> > >  # elif defined(__powerpc__)
> > > @@ -1582,6 +1584,10 @@ TEST_F(TRACE_poke, getpid_runs_normally)
> > >  # define ARCH_REGS	struct user_pt_regs
> > >  # define SYSCALL_NUM	regs[8]
> > >  # define SYSCALL_RET	regs[0]
> > > +#elif defined(__riscv) && __riscv_xlen == 64
> > > +# define ARCH_REGS	struct user_regs_struct
> > > +# define SYSCALL_NUM	a7
> > > +# define SYSCALL_RET	a0
> > >  #elif defined(__hppa__)
> > >  # define ARCH_REGS	struct user_regs_struct
> > >  # define SYSCALL_NUM	gr[20]
> > > @@ -1671,7 +1677,7 @@ void change_syscall(struct __test_metadata *_metadata,
> > >  	EXPECT_EQ(0, ret) {}
> > >  
> > >  #if defined(__x86_64__) || defined(__i386__) || defined(__powerpc__) || \
> > > -    defined(__s390__) || defined(__hppa__)
> > > +    defined(__s390__) || defined(__hppa__) || defined(__riscv)
> > >  	{
> > >  		regs.SYSCALL_NUM = syscall;
> > >  	}
> > > -- 
> > > 2.21.0
> > > 
> > > 
> > 
> > 
> > - Paul
> > 
> 
> 

-- 
Kees Cook