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>

1 files changed, 9 insertions, 5 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index beaab68c13b7..66aef13f6038 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -219,11 +219,15 @@ config ARCH_WANT_OLD_COMPAT_IPC
 config HAVE_ARCH_SECCOMP_FILTER
         bool
         help
-          This symbol should be selected by an architecure if it provides
-          asm/syscall.h, specifically syscall_get_arguments(),
-          syscall_get_arch(), and syscall_set_return_value().  Additionally,
-          its system call entry path must respect a return value of -1 from
-          __secure_computing() and/or secure_computing().
+          This symbol should be selected by an architecure if it provides:
+          asm/syscall.h:
+          - syscall_get_arch()
+          - syscall_get_arguments()
+          - syscall_rollback()
+          - syscall_set_return_value()
+          SIGSYS siginfo_t support must be implemented.
+          __secure_computing()/secure_computing()'s return value must be
+          checked, with -1 resulting in the syscall being skipped.
 
 config SECCOMP_FILTER
         def_bool y