powerpc/kernel: Add SIG_SYS support for compat tasks

SIG_SYS was added in commit a0727e8ce513 "signal, x86: add SIGSYS info
and make it synchronous."

Because we use the asm-generic struct siginfo, we got support for
SIG_SYS for free as part of that commit.

However there was no compat handling added for powerpc. That means we've
been advertising the existence of signfo._sifields._sigsys to compat
tasks, but not actually filling in the fields correctly.

Luckily it looks like no one has noticed, presumably because the only
user of SIGSYS in the kernel is seccomp filter, which we don't support
yet.

So before we enable seccomp filter, add compat handling for SIGSYS.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Kees Cook <keescook@chromium.org>

arch/powerpc/include/asm/compat.h

@@ -174,6 +174,13 @@ typedef struct compat_siginfo {
 			int _band;	/* POLL_IN, POLL_OUT, POLL_MSG */
 			int _fd;
 		} _sigpoll;
+
+		/* SIGSYS */
+		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;
 

arch/powerpc/kernel/signal_32.c

@@ -949,6 +949,11 @@ int copy_siginfo_to_user32(struct compat_siginfo __user *d, const siginfo_t *s)
 		err |= __put_user(s->si_overrun, &d->si_overrun);
 		err |= __put_user(s->si_int, &d->si_int);
 		break;
+	case __SI_SYS >> 16:
+		err |= __put_user(ptr_to_compat(s->si_call_addr), &d->si_call_addr);
+		err |= __put_user(s->si_syscall, &d->si_syscall);
+		err |= __put_user(s->si_arch, &d->si_arch);
+		break;
 	case __SI_RT >> 16: /* This is not generated by the kernel as of now.  */
 	case __SI_MESGQ >> 16:
 		err |= __put_user(s->si_int, &d->si_int);