mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 19:43:32 +00:00
107 lines
4.8 KiB
C
107 lines
4.8 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#define ShouldUseMsabiAttribute() 1
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#include "ape/sections.internal.h"
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#include "libc/dce.h"
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#include "libc/errno.h"
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#include "libc/intrin/asmflag.h"
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#include "libc/intrin/kprintf.h"
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#include "libc/nt/enum/pageflags.h"
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#include "libc/nt/memory.h"
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#include "libc/nt/thunk/msabi.h"
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#include "libc/runtime/runtime.h"
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#include "libc/sysv/consts/nr.h"
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#include "libc/sysv/consts/prot.h"
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__msabi extern typeof(VirtualProtect) *const __imp_VirtualProtect;
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__funline void __morph_mprotect(void *addr, size_t size, int prot, int ntprot) {
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#ifdef __x86_64__
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bool cf;
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int ax, dx;
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uint32_t op;
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if (!IsWindows()) {
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asm volatile(CFLAG_ASM("clc\n\t"
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"syscall")
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: CFLAG_CONSTRAINT(cf), "=a"(ax), "=d"(dx)
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: "1"(__NR_mprotect), "D"(addr), "S"(size), "2"(prot)
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: "rcx", "r8", "r9", "r10", "r11", "memory");
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#ifndef NDEBUG
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if (cf) ax = -ax;
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if (ax == -EPERM) {
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kprintf("error: need pledge(prot_exec) permission to code morph\n");
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}
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if (ax < 0) {
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kprintf("error: __morph_mprotect(%p, %#zx, %d) failed: errno=%d\n", addr,
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size, prot, -ax);
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}
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#endif
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} else {
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__imp_VirtualProtect(addr, size, ntprot, &op);
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}
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#elif defined(__aarch64__)
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register long r0 asm("x0") = (long)addr;
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register long r1 asm("x1") = (long)size;
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register long r2 asm("x2") = (long)prot;
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register long r8 asm("x8") = (long)__NR_mprotect;
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register long r16 asm("x16") = (long)__NR_mprotect;
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asm volatile("svc\t0"
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: "+r"(r0)
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: "r"(r1), "r"(r2), "r"(r8), "r"(r16)
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: "memory");
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#endif
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}
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/**
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* Begins code morphing executable.
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*
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* The following example
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*
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* #include <cosmo.h>
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* #include <stdlib.h>
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*
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* privileged int main() { // privileged code is unmodifiable
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* ShowCrashReports(); // print report if trapped
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* __morph_begin(0); // make executable code R+W
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* *(char *)exit = 0xCC; // turn exit() into an INT3 trap
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* __morph_end(); // make executable code R+X
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* exit(0); // won't actually exit
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* }
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*
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* shows how the exit() function can be recompiled at runtime to become
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* an int3 (x86-64) debugger trap. What makes it tricky is Cosmopolitan
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* maintains a R^X invariant, in order to support OpenBSD. So when code
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* wants to modify some part of the executable image in memory the vast
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* majority of the code stops being executable during that time, unless
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* it's been linked into a special privileged section of the binary. It
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* is only possible to code morph from privileged functions. Privileged
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* functions are also only allowed to call other privileged functions.
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*/
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privileged void __morph_begin(void) {
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__morph_mprotect(__executable_start, __privileged_start - __executable_start,
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PROT_READ | PROT_WRITE, kNtPageWritecopy);
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}
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/**
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* Finishes code morphing executable.
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*/
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privileged void __morph_end(void) {
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__morph_mprotect(__executable_start, __privileged_start - __executable_start,
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PROT_READ | PROT_EXEC, kNtPageExecuteRead);
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}
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