riscv: add support for seccomp

Signed-off-by: Palmer Dabbelt <[email protected]>

Author: terpstra

arch/riscv/Kconfig

@@ -19,6 +19,7 @@ config RISCV
 	select GENERIC_STRNLEN_USER
 	select GENERIC_SMP_IDLE_THREAD
 	select GENERIC_ATOMIC64 if !64BIT || !RISCV_ISA_A
+	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_MEMBLOCK
 	select HAVE_MEMBLOCK_NODE_MAP
 	select HAVE_DMA_API_DEBUG
@@ -310,6 +311,22 @@ config CMDLINE_FORCE
 
 	  If you don't know what to do here, say N.
 
+config SECCOMP
+	bool
+	prompt "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.
+
+	  If unsure, say Y. Only embedded should say N here.
+
 config EARLY_PRINTK
 	def_bool y
 

arch/riscv/include/asm/elf.h

@@ -16,9 +16,6 @@
 #include <asm/auxvec.h>
 #include <asm/byteorder.h>
 
-/* TODO: Move definition into include/uapi/linux/elf-em.h */
-#define EM_RISCV	0xF3
-
 /*
  * These are used to set parameters in the core dumps.
  */

arch/riscv/include/asm/seccomp.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_SECCOMP_H
+#define _ASM_RISCV_SECCOMP_H
+
+#include <asm/unistd.h>
+
+#ifdef CONFIG_COMPAT
+#include <asm/ia32_unistd.h>
+#define __NR_seccomp_read_32		__NR_ia32_read
+#define __NR_seccomp_write_32		__NR_ia32_write
+#define __NR_seccomp_exit_32		__NR_ia32_exit
+#define __NR_seccomp_sigreturn_32	__NR_ia32_sigreturn
+#endif
+
+#include <asm-generic/seccomp.h>
+
+#endif /* _ASM_RISCV_SECCOMP_H */

arch/riscv/include/asm/syscall.h

@@ -19,6 +19,7 @@
 #define _ASM_RISCV_SYSCALL_H
 
 #include <linux/sched.h>
+#include <uapi/linux/audit.h>
 #include <linux/err.h>
 
 /* The array of function pointers for syscalls. */
@@ -99,4 +100,9 @@ static inline void syscall_set_arguments(struct task_struct *task,
 	memcpy(&regs->a1 + i * sizeof(regs->a1), args, n * sizeof(regs->a0));
 }
 
+static inline int syscall_get_arch(void)
+{
+	return AUDIT_ARCH_RISCV;
+}
+
 #endif	/* _ASM_RISCV_SYSCALL_H */

arch/riscv/include/asm/thread_info.h

@@ -80,6 +80,7 @@ struct thread_info {
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
 #define TIF_MEMDIE		5	/* is terminating due to OOM killer */
 #define TIF_SYSCALL_TRACEPOINT  6       /* syscall tracepoint instrumentation */
+#define TIF_SECCOMP		7	/* seccomp syscall filtering active */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)

include/uapi/linux/audit.h

@@ -396,6 +396,7 @@ enum {
 /* do not define AUDIT_ARCH_PPCLE since it is not supported by audit */
 #define AUDIT_ARCH_PPC64	(EM_PPC64|__AUDIT_ARCH_64BIT)
 #define AUDIT_ARCH_PPC64LE	(EM_PPC64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
+#define AUDIT_ARCH_RISCV	(EM_RISCV)
 #define AUDIT_ARCH_S390		(EM_S390)
 #define AUDIT_ARCH_S390X	(EM_S390|__AUDIT_ARCH_64BIT)
 #define AUDIT_ARCH_SH		(EM_SH)

include/uapi/linux/elf-em.h

@@ -41,6 +41,7 @@
 #define EM_TILEPRO	188	/* Tilera TILEPro */
 #define EM_MICROBLAZE	189	/* Xilinx MicroBlaze */
 #define EM_TILEGX	191	/* Tilera TILE-Gx */
+#define EM_RISCV	243	/* RISC-V */
 #define EM_BPF		247	/* Linux BPF - in-kernel virtual machine */
 #define EM_FRV		0x5441	/* Fujitsu FR-V */