tile: enable full SECCOMP support

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

Documentation/features/seccomp/seccomp-filter/arch-support.txt

@@ -32,7 +32,7 @@
     |       score: | TODO |
     |          sh: | TODO |
     |       sparc: | TODO |
-    |        tile: | TODO |
+    |        tile: |  ok  |
     |          um: | TODO |
     |   unicore32: | TODO |
     |         x86: |  ok  |

arch/tile/Kconfig

@@ -32,6 +32,7 @@ config TILE
 	select EDAC_SUPPORT
 	select GENERIC_STRNCPY_FROM_USER
 	select GENERIC_STRNLEN_USER
+	select HAVE_ARCH_SECCOMP_FILTER
 
 # FIXME: investigate whether we need/want these options.
 #	select HAVE_IOREMAP_PROT
@@ -221,6 +222,22 @@ config COMPAT
 	  If enabled, the kernel will support running TILE-Gx binaries
 	  that were built with the -m32 option.
 
+config SECCOMP
+	bool "Enable seccomp to safely compute untrusted bytecode"
+	depends on PROC_FS
+	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, it cannot be disabled and the task is only
+	  allowed to execute a few safe syscalls defined by each seccomp
+	  mode.
+
+	  If unsure, say N.
+
 config SYSVIPC_COMPAT
 	def_bool y
 	depends on COMPAT && SYSVIPC

arch/tile/include/asm/Kbuild

@@ -28,6 +28,7 @@ generic-y += poll.h
 generic-y += posix_types.h
 generic-y += preempt.h
 generic-y += resource.h
+generic-y += seccomp.h
 generic-y += sembuf.h
 generic-y += serial.h
 generic-y += shmbuf.h

arch/tile/include/asm/elf.h

@@ -22,6 +22,7 @@
 #include <arch/chip.h>
 
 #include <linux/ptrace.h>
+#include <linux/elf-em.h>
 #include <asm/byteorder.h>
 #include <asm/page.h>
 
@@ -30,9 +31,6 @@ typedef unsigned long elf_greg_t;
 #define ELF_NGREG (sizeof(struct pt_regs) / sizeof(elf_greg_t))
 typedef elf_greg_t elf_gregset_t[ELF_NGREG];
 
-#define EM_TILEPRO 188
-#define EM_TILEGX  191
-
 /* Provide a nominal data structure. */
 #define ELF_NFPREG	0
 typedef double elf_fpreg_t;

arch/tile/include/asm/syscall.h

@@ -20,6 +20,8 @@
 
 #include <linux/sched.h>
 #include <linux/err.h>
+#include <linux/audit.h>
+#include <linux/compat.h>
 #include <arch/abi.h>
 
 /* The array of function pointers for syscalls. */
@@ -61,7 +63,15 @@ static inline void syscall_set_return_value(struct task_struct *task,
 					    struct pt_regs *regs,
 					    int error, long val)
 {
-	regs->regs[0] = (long) error ?: val;
+	if (error) {
+		/* R0 is the passed-in negative error, R1 is positive. */
+		regs->regs[0] = error;
+		regs->regs[1] = -error;
+	} else {
+		/* R1 set to zero to indicate no error. */
+		regs->regs[0] = val;
+		regs->regs[1] = 0;
+	}
 }
 
 static inline void syscall_get_arguments(struct task_struct *task,
@@ -82,4 +92,20 @@ static inline void syscall_set_arguments(struct task_struct *task,
 	memcpy(&regs[i], args, n * sizeof(args[0]));
 }
 
+/*
+ * We don't care about endianness (__AUDIT_ARCH_LE bit) here because
+ * tile has the same system calls both on little- and big- endian.
+ */
+static inline int syscall_get_arch(void)
+{
+	if (is_compat_task())
+		return AUDIT_ARCH_TILEGX32;
+
+#ifdef CONFIG_TILEGX
+	return AUDIT_ARCH_TILEGX;
+#else
+	return AUDIT_ARCH_TILEPRO;
+#endif
+}
+
 #endif	/* _ASM_TILE_SYSCALL_H */

arch/tile/kernel/intvec_32.S

@@ -1224,6 +1224,7 @@ handle_syscall:
 	 jal    do_syscall_trace_enter
 	}
 	FEEDBACK_REENTER(handle_syscall)
+	blz     r0, .Lsyscall_sigreturn_skip
 
 	/*
 	 * We always reload our registers from the stack at this

arch/tile/kernel/intvec_64.S

@@ -1247,6 +1247,7 @@ handle_syscall:
 	 jal    do_syscall_trace_enter
 	}
 	FEEDBACK_REENTER(handle_syscall)
+	bltz    r0, .Lsyscall_sigreturn_skip
 
 	/*
 	 * We always reload our registers from the stack at this

arch/tile/kernel/ptrace.c

@@ -262,6 +262,9 @@ int do_syscall_trace_enter(struct pt_regs *regs)
 	if (work & _TIF_NOHZ)
 		user_exit();
 
+	if (secure_computing() == -1)
+		return -1;
+
 	if (work & _TIF_SYSCALL_TRACE) {
 		if (tracehook_report_syscall_entry(regs))
 			regs->regs[TREG_SYSCALL_NR] = -1;

include/uapi/linux/audit.h

@@ -382,6 +382,9 @@ enum {
 #define AUDIT_ARCH_SHEL64	(EM_SH|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
 #define AUDIT_ARCH_SPARC	(EM_SPARC)
 #define AUDIT_ARCH_SPARC64	(EM_SPARCV9|__AUDIT_ARCH_64BIT)
+#define AUDIT_ARCH_TILEGX	(EM_TILEGX|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
+#define AUDIT_ARCH_TILEGX32	(EM_TILEGX|__AUDIT_ARCH_LE)
+#define AUDIT_ARCH_TILEPRO	(EM_TILEPRO|__AUDIT_ARCH_LE)
 #define AUDIT_ARCH_X86_64	(EM_X86_64|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
 
 #define AUDIT_PERM_EXEC		1

include/uapi/linux/elf-em.h

@@ -38,6 +38,8 @@
 #define EM_ALTERA_NIOS2	113	/* Altera Nios II soft-core processor */
 #define EM_TI_C6000	140	/* TI C6X DSPs */
 #define EM_AARCH64	183	/* ARM 64 bit */
+#define EM_TILEPRO	188	/* Tilera TILEPro */
+#define EM_TILEGX	191	/* Tilera TILE-Gx */
 #define EM_FRV		0x5441	/* Fujitsu FR-V */
 #define EM_AVR32	0x18ad	/* Atmel AVR32 */