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, 22 insertions, 0 deletions

diff --git a/include/asm-generic/siginfo.h b/include/asm-generic/siginfo.h
index 0dd4e87f6fba..31306f55eb02 100644
--- a/include/asm-generic/siginfo.h
+++ b/include/asm-generic/siginfo.h
@@ -90,9 +90,18 @@ typedef struct siginfo {
                         __ARCH_SI_BAND_T _band; /* POLL_IN, POLL_OUT, POLL_MSG */
                         int _fd;
                 } _sigpoll;
+
+                /* SIGSYS */
+                struct {
+                        void __user *_call_addr; /* calling insn */
+                        int _syscall;   /* triggering system call number */
+                        unsigned int _arch;     /* AUDIT_ARCH_* of syscall */
+                } _sigsys;
         } _sifields;
 } siginfo_t;
 
+/* If the arch shares siginfo, then it has SIGSYS. */
+#define __ARCH_SIGSYS
 #endif
 
 /*
@@ -116,6 +125,11 @@ typedef struct siginfo {
 #define si_addr_lsb     _sifields._sigfault._addr_lsb
 #define si_band         _sifields._sigpoll._band
 #define si_fd           _sifields._sigpoll._fd
+#ifdef __ARCH_SIGSYS
+#define si_call_addr    _sifields._sigsys._call_addr
+#define si_syscall      _sifields._sigsys._syscall
+#define si_arch         _sifields._sigsys._arch
+#endif
 
 #ifdef __KERNEL__
 #define __SI_MASK       0xffff0000u
@@ -126,6 +140,7 @@ typedef struct siginfo {
 #define __SI_CHLD       (4 << 16)
 #define __SI_RT         (5 << 16)
 #define __SI_MESGQ      (6 << 16)
+#define __SI_SYS        (7 << 16)
 #define __SI_CODE(T,N)  ((T) | ((N) & 0xffff))
 #else
 #define __SI_KILL       0
@@ -135,6 +150,7 @@ typedef struct siginfo {
 #define __SI_CHLD       0
 #define __SI_RT         0
 #define __SI_MESGQ      0
+#define __SI_SYS        0
 #define __SI_CODE(T,N)  (N)
 #endif
 
@@ -232,6 +248,12 @@ typedef struct siginfo {
 #define NSIGPOLL        6
 
 /*
+ * SIGSYS si_codes
+ */
+#define SYS_SECCOMP             (__SI_SYS|1)    /* seccomp triggered */
+#define NSIGSYS 1
+
+/*
  * sigevent definitions
  * 
  * It seems likely that SIGEV_THREAD will have to be handled from