fix wrong sigaction syscall ABI on mips*, or1k, microblaze, riscv64

we wrongly defined a dummy SA_RESTORER flag on these archs, despite
the kernel interface not actually having such a feature. on archs
which lack SA_RESTORER, the kernel sigaction structure also lacks the
restorer function pointer member, which means the signal mask appears
at a different offset. the kernel was thereby interpreting the bits of
the code address as part of the signal set to be masked while handling
the signal.

this patch removes the erroneous SA_RESTORER definitions from archs
which do not have it, makes access to the member conditional on
whether SA_RESTORER is defined for the arch, and removes the
now-unused asm for the affected archs.

because there are reportedly versions of qemu-user which also use the
wrong ABI here, the old ksigaction struct size is preserved with an
unused member at the end. this is harmless and mitigates the risk of
such a bug turning into a buffer overflow onto the sigaction
function's stack.

5 files changed, 9 insertions, 38 deletions

diff --git a/src/internal/ksigaction.h b/src/internal/ksigaction.h
index 8ebd5938..ef333f33 100644
--- a/src/internal/ksigaction.h
+++ b/src/internal/ksigaction.h
@@ -6,8 +6,13 @@
 struct k_sigaction {
 	void (*handler)(int);
 	unsigned long flags;
+#ifdef SA_RESTORER
 	void (*restorer)(void);
+#endif
 	unsigned mask[2];
+#ifndef SA_RESTORER
+	void *unused;
+#endif
 };
 
 hidden void __restore(), __restore_rt();
diff --git a/src/signal/mips/restore.s b/src/signal/mips/restore.s
deleted file mode 100644
index b6dadce0..00000000
--- a/src/signal/mips/restore.s
+++ /dev/null
@@ -1,15 +0,0 @@
-.set noreorder
-
-.global __restore_rt
-.hidden __restore_rt
-.type   __restore_rt,@function
-__restore_rt:
-	li $2, 4193
-	syscall
-
-.global __restore
-.hidden __restore
-.type   __restore,@function
-__restore:
-	li $2, 4119
-	syscall
diff --git a/src/signal/mips64/restore.s b/src/signal/mips64/restore.s
deleted file mode 100644
index 401f8e73..00000000
--- a/src/signal/mips64/restore.s
+++ /dev/null
@@ -1,11 +0,0 @@
-.set	noreorder
-.global	__restore_rt
-.global	__restore
-.hidden __restore_rt
-.hidden __restore
-.type	__restore_rt,@function
-.type	__restore,@function
-__restore_rt:
-__restore:
-	li	$2,5211
-	syscall
diff --git a/src/signal/mipsn32/restore.s b/src/signal/mipsn32/restore.s
deleted file mode 100644
index 4cd4e1b4..00000000
--- a/src/signal/mipsn32/restore.s
+++ /dev/null
@@ -1,11 +0,0 @@
-.set	noreorder
-.global	__restore_rt
-.global	__restore
-.hidden __restore_rt
-.hidden __restore
-.type	__restore_rt,@function
-.type	__restore,@function
-__restore_rt:
-__restore:
-	li	$2,6211
-	syscall
diff --git a/src/signal/sigaction.c b/src/signal/sigaction.c
index 2203471b..e45308fa 100644
--- a/src/signal/sigaction.c
+++ b/src/signal/sigaction.c
@@ -44,8 +44,11 @@ int __libc_sigaction(int sig, const struct sigaction *restrict sa, struct sigact
 			}
 		}
 		ksa.handler = sa->sa_handler;
-		ksa.flags = sa->sa_flags | SA_RESTORER;
+		ksa.flags = sa->sa_flags;
+#ifdef SA_RESTORER
+		ksa.flags |= SA_RESTORER;
 		ksa.restorer = (sa->sa_flags & SA_SIGINFO) ? __restore_rt : __restore;
+#endif
 		memcpy(&ksa.mask, &sa->sa_mask, _NSIG/8);
 	}
 	int r = __syscall(SYS_rt_sigaction, sig, sa?&ksa:0, old?&ksa_old:0, _NSIG/8);