add support for arbitrary syscalls

Thanks for the idea, sleirsgoevy

crt/Makefile

@@ -24,7 +24,7 @@ CFLAGS  += -mcmodel=large -fPIC -fno-plt -masm=intel
 
 all: crt1.o
 
-crt1.o: crt.o kernel.o sprx.o
+crt1.o: crt.o kernel.o sprx.o syscall.o
 	$(LD) -r -o $@ $^
 
 %.o: %.c

crt/syscall.c

@@ -0,0 +1,43 @@
+/* Copyright (C) 2023 John Törnblom
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; see the file COPYING. If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include "payload.h"
+
+
+static __attribute__ ((used)) long ptr_syscall;
+
+
+asm(".intel_syntax noprefix\n"
+    ".global syscall\n"
+    ".type syscall @function\n"
+    "syscall:\n"
+    "  mov rax, rdi\n"                      // sysno
+    "  mov rdi, rsi\n"                      // arg1
+    "  mov rsi, rdx\n"                      // arg2
+    "  mov rdx, rcx\n"                      // arg3
+    "  mov r10, r8\n"                       // arg4
+    "  mov r8,  r9\n"                       // arg5
+    "  mov r9,  qword ptr [rsp + 8]\n"      // arg6
+    "  jmp qword ptr [rip + ptr_syscall]\n" // syscall
+    "  ret\n"
+    );
+
+
+__attribute__((constructor(101))) static void
+constructor(const payload_args_t *args) {
+  *args->payloadout = args->sceKernelDlsym(0x2001, "getpid", &ptr_syscall);
+  ptr_syscall += 0xa; // jump directly to syscall instruction
+}

samples/arbitrary_syscall/.gitignore

@@ -0,0 +1,4 @@
+*.elf
+*.o
+*~
+

samples/arbitrary_syscall/Makefile

@@ -0,0 +1,45 @@
+#   Copyright (C) 2023 John Törnblom
+#
+# This file is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; see the file COPYING. If not see
+# <http://www.gnu.org/licenses/>.
+
+ifndef PS5_PAYLOAD_SDK
+    $(error PS5_PAYLOAD_SDK is undefined)
+endif
+
+PS5_HOST ?= ps5
+PS5_PORT ?= 9020
+
+ELF := arbitrary_syscall.elf
+
+CC := $(PS5_PAYLOAD_SDK)/host/x86_64-ps5-payload-cc
+LD := $(PS5_PAYLOAD_SDK)/host/x86_64-ps5-payload-ld
+
+CFLAGS := -O2
+LDADD  := -lSceLibcInternal
+
+all: $(ELF)
+
+%.o: %.c
+	$(CC) -c $(CFLAGS) -o $@ $^
+
+$(ELF): main.o
+	$(LD) $^ $(LDADD) -o $@
+
+clean:
+	rm -f *.o $(ELF)
+
+test: $(ELF)
+	nc -q0 $(PS5_HOST) $(PS5_PORT) < $^
+

samples/arbitrary_syscall/main.c

@@ -0,0 +1,26 @@
+/* Copyright (C) 2023 John Törnblom
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; see the file COPYING. If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+
+int main() {
+  printf("%d\n", (int)syscall(SYS_getuid));
+
+  return 0;
+}