signal, x86: add SIGSYS info and make it synchronous.

This change enables SIGSYS, defines _sigfields._sigsys, and adds
x86 (compat) arch support.  _sigsys defines fields which allow
a signal handler to receive the triggering system call number,
the relevant AUDIT_ARCH_* value for that number, and the address
of the callsite.

SIGSYS is added to the SYNCHRONOUS_MASK because it is desirable for it
to have setup_frame() called for it. The goal is to ensure that
ucontext_t reflects the machine state from the time-of-syscall and not
from another signal handler.

The first consumer of SIGSYS would be seccomp filter.  In particular,
a filter program could specify a new return value, SECCOMP_RET_TRAP,
which would result in the system call being denied and the calling
thread signaled.  This also means that implementing arch-specific
support can be dependent upon HAVE_ARCH_SECCOMP_FILTER.

Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Reviewed-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Eric Paris <eparis@redhat.com>

v18: - added acked by, rebase
v17: - rebase and reviewed-by addition
v14: - rebase/nochanges
v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
v12: - reworded changelog (oleg@redhat.com)
v11: - fix dropped words in the change description
     - added fallback copy_siginfo support.
     - added __ARCH_SIGSYS define to allow stepped arch support.
v10: - first version based on suggestion
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/include/asm/ia32.h b/arch/x86/include/asm/ia32.h
index ee52760..b04cbdb 100644
--- a/arch/x86/include/asm/ia32.h
+++ b/arch/x86/include/asm/ia32.h
@@ -144,6 +144,12 @@ typedef struct compat_siginfo {
 			int _band;	/* POLL_IN, POLL_OUT, POLL_MSG */
 			int _fd;
 		} _sigpoll;
+
+		struct {
+			unsigned int _call_addr; /* calling insn */
+			int _syscall;	/* triggering system call number */
+			unsigned int _arch;	/* AUDIT_ARCH_* of syscall */
+		} _sigsys;
 	} _sifields;
 } compat_siginfo_t;