ptrace,seccomp: Add PTRACE_SECCOMP support

This change adds support for a new ptrace option, PTRACE_O_TRACESECCOMP,
and a new return value for seccomp BPF programs, SECCOMP_RET_TRACE.

When a tracer specifies the PTRACE_O_TRACESECCOMP ptrace option, the
tracer will be notified, via PTRACE_EVENT_SECCOMP, for any syscall that
results in a BPF program returning SECCOMP_RET_TRACE.  The 16-bit
SECCOMP_RET_DATA mask of the BPF program return value will be passed as
the ptrace_message and may be retrieved using PTRACE_GETEVENTMSG.

If the subordinate process is not using seccomp filter, then no
system call notifications will occur even if the option is specified.

If there is no tracer with PTRACE_O_TRACESECCOMP when SECCOMP_RET_TRACE
is returned, the system call will not be executed and an -ENOSYS errno
will be returned to userspace.

This change adds a dependency on the system call slow path.  Any future
efforts to use the system call fast path for seccomp filter will need to
address this restriction.

Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Eric Paris <eparis@redhat.com>

v18: - rebase
     - comment fatal_signal check
     - acked-by
     - drop secure_computing_int comment
v17: - ...
v16: - update PT_TRACE_MASK to 0xbf4 so that STOP isn't clear on SETOPTIONS call (indan@nul.nu)
       [note PT_TRACE_MASK disappears in linux-next]
v15: - add audit support for non-zero return codes
     - clean up style (indan@nul.nu)
v14: - rebase/nochanges
v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
       (Brings back a change to ptrace.c and the masks.)
v12: - rebase to linux-next
     - use ptrace_event and update arch/Kconfig to mention slow-path dependency
     - drop all tracehook changes and inclusion (oleg@redhat.com)
v11: - invert the logic to just make it a PTRACE_SYSCALL accelerator
       (indan@nul.nu)
v10: - moved to PTRACE_O_SECCOMP / PT_TRACE_SECCOMP
v9:  - n/a
v8:  - guarded PTRACE_SECCOMP use with an ifdef
v7:  - introduced
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 5c719627c2aa..597e4fdb97fe 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -58,6 +58,7 @@
 #define PTRACE_EVENT_EXEC       4
 #define PTRACE_EVENT_VFORK_DONE 5
 #define PTRACE_EVENT_EXIT       6
+#define PTRACE_EVENT_SECCOMP    7
 /* Extended result codes which enabled by means other than options.  */
 #define PTRACE_EVENT_STOP       128
 
@@ -69,8 +70,9 @@
 #define PTRACE_O_TRACEEXEC      (1 << PTRACE_EVENT_EXEC)
 #define PTRACE_O_TRACEVFORKDONE (1 << PTRACE_EVENT_VFORK_DONE)
 #define PTRACE_O_TRACEEXIT      (1 << PTRACE_EVENT_EXIT)
+#define PTRACE_O_TRACESECCOMP   (1 << PTRACE_EVENT_SECCOMP)
 
-#define PTRACE_O_MASK           0x0000007f
+#define PTRACE_O_MASK           0x000000ff
 
 #include <asm/ptrace.h>
 
@@ -98,6 +100,7 @@
 #define PT_TRACE_EXEC           PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
 #define PT_TRACE_VFORK_DONE     PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
 #define PT_TRACE_EXIT           PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
+#define PT_TRACE_SECCOMP        PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)
 
 /* single stepping state bits (used on ARM and PA-RISC) */
 #define PT_SINGLESTEP_BIT       31