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References: <20190822205533.4877-1-david.abdurachmanov@sifive.com>
In-Reply-To: <20190822205533.4877-1-david.abdurachmanov@sifive.com>
From:   Carlos Eduardo de Paula <me@carlosedp.com>
Date:   Fri, 23 Aug 2019 19:54:01 -0300
Message-ID: <CADnnUqe2Phwy7cUAaawLzcBLbMtHKvJPr9Gmn9zQsVSGf_K=VA@mail.gmail.com>
Subject: Re: [PATCH v2] riscv: add support for SECCOMP and SECCOMP_FILTER
To:     David Abdurachmanov <david.abdurachmanov@gmail.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Oleg Nesterov <oleg@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Will Drewry <wad@chromium.org>, Shuah Khan <shuah@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        David Abdurachmanov <david.abdurachmanov@sifive.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Allison Randal <allison@lohutok.net>,
        Alexios Zavras <alexios.zavras@intel.com>,
        Anup Patel <Anup.Patel@wdc.com>,
        Vincent Chen <vincentc@andestech.com>,
        Alan Kao <alankao@andestech.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, netdev@vger.kernel.org,
        bpf@vger.kernel.org
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On Thu, Aug 22, 2019 at 5:56 PM David Abdurachmanov
<david.abdurachmanov@gmail.com> 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@chromium.org
> Cc: me@carlosedp.com
>
> Signed-off-by: David Abdurachmanov <david.abdurachmanov@sifive.com>
> ---
>  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
>

Tested-by: Carlos de Paula <me@carlosedp.com>
-- 
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