[PATCH v2] riscv: add support for SECCOMP and SECCOMP_FILTER
From: David Abdurachmanov
Date: Thu Aug 22 2019 - 16:56:08 EST
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>
---
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