seccomp: Add SECCOMP_RET_TRAP

Adds a new return value to seccomp filters that triggers a SIGSYS to be
delivered with the new SYS_SECCOMP si_code.

This allows in-process system call emulation, including just specifying
an errno or cleanly dumping core, rather than just dying.

Suggested-by: Markus Gutschke <markus@chromium.org>
Suggested-by: Julien Tinnes <jln@chromium.org>
Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Eric Paris <eparis@redhat.com>

v18: - acked-by, rebase
     - don't mention secure_computing_int() anymore
v15: - use audit_seccomp/skip
     - pad out error spacing; clean up switch (indan@nul.nu)
v14: - n/a
v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
v12: - rebase on to linux-next
v11: - clarify the comment (indan@nul.nu)
     - s/sigtrap/sigsys
v10: - use SIGSYS, syscall_get_arch, updates arch/Kconfig
       note suggested-by (though original suggestion had other behaviors)
v9:  - changes to SIGILL
v8:  - clean up based on changes to dependent patches
v7:  - introduction
Signed-off-by: James Morris <james.l.morris@oracle.com>

2 files changed, 2 insertions, 1 deletions

diff --git a/include/asm-generic/siginfo.h b/include/asm-generic/siginfo.h
index 31306f55eb0..af5d0350f84 100644
--- a/include/asm-generic/siginfo.h
+++ b/include/asm-generic/siginfo.h
@@ -93,7 +93,7 @@ typedef struct siginfo {
 
                 /* SIGSYS */
                 struct {
-                        void __user *_call_addr; /* calling insn */
+                        void __user *_call_addr; /* calling user insn */
                         int _syscall;   /* triggering system call number */
                         unsigned int _arch;     /* AUDIT_ARCH_* of syscall */
                 } _sigsys;
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index b4ce2c816e0..317ccb78cf4 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -19,6 +19,7 @@
  * selects the least permissive choice.
  */
 #define SECCOMP_RET_KILL        0x00000000U /* kill the task immediately */
+#define SECCOMP_RET_TRAP        0x00030000U /* disallow and force a SIGSYS */
 #define SECCOMP_RET_ERRNO       0x00050000U /* returns an errno */
 #define SECCOMP_RET_ALLOW       0x7fff0000U /* allow */