From c0a6b811701bdbfe01fb72ed4246ca86eedef8aa Mon Sep 17 00:00:00 2001
From: anton <anton@openbsd.org>
Date: Mon, 9 Jan 2023 11:50:01 +0000
Subject: [PATCH] Fix the syscallwx target which is affected by both
 mimmutable(2) and xonly by using a new gadget routine written in assembler
 with the sole purpose of issuing a syscall. Since it needs to be copied to wx
 memory, place it in the rodata section.

---
 regress/usr.bin/lastcomm/Makefile    |  3 ++-
 regress/usr.bin/lastcomm/gadget.S    | 28 ++++++++++++++++++++++++++
 regress/usr.bin/lastcomm/syscallwx.c | 30 ++++++++++++++++------------
 3 files changed, 47 insertions(+), 14 deletions(-)
 create mode 100644 regress/usr.bin/lastcomm/gadget.S

diff --git a/regress/usr.bin/lastcomm/Makefile b/regress/usr.bin/lastcomm/Makefile
index f05b16e083d..b9a97649e73 100644
--- a/regress/usr.bin/lastcomm/Makefile
+++ b/regress/usr.bin/lastcomm/Makefile
@@ -1,4 +1,4 @@
-# $OpenBSD: Makefile,v 1.10 2021/09/28 08:51:18 kettenis Exp $
+# $OpenBSD: Makefile,v 1.11 2023/01/09 11:50:01 anton Exp $
 
 # Start with a clean /var/account/acct accounting file and turn on
 # process accounting with accton(8).  Each test executes a command
@@ -22,6 +22,7 @@ REGRESS_EXPECTED_FAILURES +=	run-callstack run-syscallwx
 
 PROGS=			crash trapstack callstack syscallwx unveil
 WARNINGS=		Yes
+SRCS_syscallwx=		syscallwx.c gadget.S
 LDADD_syscallwx=	-Wl,-z,wxneeded
 CLEANFILES=		regress-*
 
diff --git a/regress/usr.bin/lastcomm/gadget.S b/regress/usr.bin/lastcomm/gadget.S
new file mode 100644
index 00000000000..dc0ca6cc8bb
--- /dev/null
+++ b/regress/usr.bin/lastcomm/gadget.S
@@ -0,0 +1,28 @@
+/*	$OpenBSD: gadget.S,v 1.1 2023/01/09 11:50:01 anton Exp $	*/
+
+#include <sys/syscall.h>
+#include <machine/asm.h>
+
+#if !defined(_ASM_TYPE_FUNCTION)
+#define _ASM_TYPE_FUNCTION @function
+#endif
+
+        .section .rodata
+        .globl	gadget_getpid
+        .type	gadget_getpid,_ASM_TYPE_FUNCTION
+gadget_getpid:
+#if defined(__amd64__)
+	mov	$SYS_getpid, %eax
+	syscall
+	ret
+#elif defined(__aarch64__)
+	ldr	x8, #SYS_getpid
+	svc	0
+	dsb	nsh
+	isb
+	ret
+#else
+#error "Missing gadget."
+#endif
+
+	.space 4096
diff --git a/regress/usr.bin/lastcomm/syscallwx.c b/regress/usr.bin/lastcomm/syscallwx.c
index 0eff81e6ff5..cc1e276ca51 100644
--- a/regress/usr.bin/lastcomm/syscallwx.c
+++ b/regress/usr.bin/lastcomm/syscallwx.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: syscallwx.c,v 1.1 2019/09/23 08:34:07 bluhm Exp $	*/
+/*	$OpenBSD: syscallwx.c,v 1.2 2023/01/09 11:50:01 anton Exp $	*/
 /*
  * Copyright (c) 2018 Todd Mortimer <mortimer@openbsd.org>
  * Copyright (c) 2019 Alexander Bluhm <bluhm@openbsd.org>
@@ -20,30 +20,34 @@
 
 #include <err.h>
 #include <signal.h>
+#include <string.h>
 #include <unistd.h>
 
-void handler(int);
+extern void gadget_getpid(void);
+static void handler(int);
 
 int
 main(int argc, char *argv[])
 {
-	pid_t pid;
-
-	pid = getpid();
-	if (pid == -1)
-		err(1, "getpid");
-	/* map kill system call in libc writeable */
-	if (mprotect(kill, 100, PROT_EXEC | PROT_WRITE | PROT_READ) == -1)
-		err(1, "mprotect");
+	union {
+		void *p;
+		void (*gadget)(void);
+	} addr;
+	int psz = getpagesize();
 
 	if (signal(SIGSEGV, handler) == SIG_ERR)
 		err(1, "signal");
-	if (kill(pid, SIGABRT) == -1)
-		err(1, "kill");
+
+	addr.p = mmap(NULL, psz, PROT_READ | PROT_WRITE | PROT_EXEC,
+	    MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (addr.p == NULL)
+		err(1, "mmap");
+	memcpy(addr.p, gadget_getpid, psz);
+	addr.gadget();
 	return 3;
 }
 
-void
+static void
 handler(int signum)
 {
 	_exit(0);
-- 
2.20.1