From 5340627e3fe08030988bdda46dd86cd5d5fb7517 Mon Sep 17 00:00:00 2001 From: David Abdurachmanov Date: Fri, 4 Oct 2019 17:12:22 -0700 Subject: riscv: add support for SECCOMP and SECCOMP_FILTER 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 immediately if secure_computing(NULL) returns -1 - fixed whitespace issues - add missing seccomp.h - remove patch #2 (solved now) - add riscv to seccomp kernel selftest Signed-off-by: David Abdurachmanov Cc: keescook@chromium.org Cc: me@carlosedp.com Tested-by: Carlos de Paula Reviewed-by: Kees Cook Link: https://lore.kernel.org/linux-riscv/CAEn-LTp=ss0Dfv6J00=rCAy+N78U2AmhqJNjfqjr2FDpPYjxEQ@mail.gmail.com/ Link: https://lore.kernel.org/linux-riscv/CAJr-aD=UnCN9E_mdVJ2H5nt=6juRSWikZnA5HxDLQxXLbsRz-w@mail.gmail.com/ [paul.walmsley@sifive.com: cleaned up Cc: lines; fixed spelling and checkpatch issues; updated to apply] Signed-off-by: Paul Walmsley --- 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 ++++++++++ 5 files changed, 63 insertions(+), 3 deletions(-) create mode 100644 arch/riscv/include/asm/seccomp.h (limited to 'arch/riscv') diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 8eebbc8860bb..bc7598fc5f00 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_ASM_MODVERSIONS select HAVE_MEMBLOCK_NODE_MAP select HAVE_DMA_CONTIGUOUS @@ -272,6 +273,19 @@ 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 + +#include + +#endif /* _ASM_SECCOMP_H */ diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h index 905372d7eeb8..1dd12a0cbb2b 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 8ca479831142..c68b987e623e 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -226,8 +226,25 @@ 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 @@ -238,6 +255,12 @@ 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 1252113ef8b2..0f84628b9385 100644 --- a/arch/riscv/kernel/ptrace.c +++ b/arch/riscv/kernel/ptrace.c @@ -154,6 +154,16 @@ __visible 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)); -- cgit v1.2.3