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

From: Paul Walmsley
Date: Fri Oct 04 2019 - 21:20:56 EST

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: keescook@xxxxxxxxxxxx
> Cc: me@xxxxxxxxxxxxx
>
> Signed-off-by: David Abdurachmanov <david.abdurachmanov@xxxxxxxxxx>

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=6juRSWikZnA5HxDLQxXLbsRz-w@xxxxxxxxxxxxxx/


- 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