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Make execve() linger when it can't spoof parent

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It's now possible to use execve() when the parent process isn't built by
cosmo. In such cases, the current process will kill all threads and then
linger around, waiting for the newly created process to die, and then we
propagate its exit code to the parent. This should help bazel and others

Allocating private anonymous memory is now 5x faster on Windows. This is
thanks to VirtualAlloc() which is faster than the file mapping APIs. The
fork() function also now goes 30% faster, since we are able to avoid the
VirtualProtect() calls on mappings in most cases now.

Fixes #1253
This commit is contained in:
Justine Tunney 2025-01-04 21:11:53 -08:00
parent c97a858470
commit 42a3bb729a
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GPG key ID: BE714B4575D6E328
40 changed files with 612 additions and 656 deletions
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135
libc/intrin/mmap.c
View file

@ -18,6 +18,7 @@
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/calls/internal.h"
#include "libc/calls/state.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/calls/syscall_support-nt.internal.h"
#include "libc/dce.h"
@ -33,10 +34,14 @@
#include "libc/intrin/weaken.h"
#include "libc/limits.h"
#include "libc/macros.h"
#include "libc/nt/enum/filemapflags.h"
#include "libc/nt/enum/memflags.h"
#include "libc/nt/enum/pageflags.h"
#include "libc/nt/errors.h"
#include "libc/nt/memory.h"
#include "libc/nt/runtime.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/syslib.internal.h"
#include "libc/runtime/zipos.internal.h"
#include "libc/stdckdint.h"
#include "libc/stdio/sysparam.h"
@ -80,6 +85,11 @@
} while (0)
#endif
struct DirectMap {
void *addr;
int64_t hand;
};
int __maps_compare(const struct Tree *ra, const struct Tree *rb) {
const struct Map *a = (const struct Map *)MAP_TREE_CONTAINER(ra);
const struct Map *b = (const struct Map *)MAP_TREE_CONTAINER(rb);
@ -421,7 +431,7 @@ void __maps_insert(struct Map *map) {
__maps_check();
}
// adds interval to rbtree (no sys_mmap)
// adds interval to rbtree
bool __maps_track(char *addr, size_t size, int prot, int flags) {
struct Map *map;
if (!(map = __maps_alloc()))
@ -447,6 +457,125 @@ int __maps_untrack(char *addr, size_t size) {
return rc;
}
textwindows dontinline static struct DirectMap sys_mmap_nt(
void *addr, size_t size, int prot, int flags, int fd, int64_t off) {
struct DirectMap dm;
// it's 5x faster
if (IsWindows() && (flags & MAP_ANONYMOUS) &&
(flags & MAP_TYPE) != MAP_SHARED) {
if (!(dm.addr = VirtualAlloc(addr, size, kNtMemReserve | kNtMemCommit,
__prot2nt(prot, false)))) {
dm.addr = MAP_FAILED;
}
dm.hand = MAPS_VIRTUAL;
return dm;
}
int64_t file_handle;
if (flags & MAP_ANONYMOUS) {
file_handle = kNtInvalidHandleValue;
} else {
file_handle = g_fds.p[fd].handle;
}
// mark map handle as inheritable if fork might need it
const struct NtSecurityAttributes *mapsec;
if ((flags & MAP_TYPE) == MAP_SHARED) {
mapsec = &kNtIsInheritable;
} else {
mapsec = 0;
}
// nt will whine under many circumstances if we change the execute bit
// later using mprotect(). the workaround is to always request execute
// and then virtualprotect() it away until we actually need it. please
// note that open-nt.c always requests an kNtGenericExecute accessmask
int iscow = 0;
int page_flags;
int file_flags;
if (file_handle != -1) {
if ((flags & MAP_TYPE) != MAP_SHARED) {
// windows has cow pages but they can't propagate across fork()
// that means we only get copy-on-write for the root process :(
page_flags = kNtPageExecuteWritecopy;
file_flags = kNtFileMapCopy | kNtFileMapExecute;
iscow = 1;
} else {
if ((g_fds.p[fd].flags & O_ACCMODE) == O_RDONLY) {
page_flags = kNtPageExecuteRead;
file_flags = kNtFileMapRead | kNtFileMapExecute;
} else {
page_flags = kNtPageExecuteReadwrite;
file_flags = kNtFileMapWrite | kNtFileMapExecute;
}
}
} else {
page_flags = kNtPageExecuteReadwrite;
file_flags = kNtFileMapWrite | kNtFileMapExecute;
}
int e = errno;
TryAgain:
if ((dm.hand = CreateFileMapping(file_handle, mapsec, page_flags,
(size + off) >> 32, (size + off), 0))) {
if ((dm.addr = MapViewOfFileEx(dm.hand, file_flags, off >> 32, off, size,
addr))) {
uint32_t oldprot;
if (VirtualProtect(dm.addr, size, __prot2nt(prot, iscow), &oldprot))
return dm;
UnmapViewOfFile(dm.addr);
}
CloseHandle(dm.hand);
} else if (!(prot & PROT_EXEC) && //
(file_flags & kNtFileMapExecute) && //
GetLastError() == kNtErrorAccessDenied) {
// your file needs to have been O_CREAT'd with exec `mode` bits in
// order to be mapped with executable permission. we always try to
// get execute permission if the kernel will give it to us because
// win32 would otherwise forbid mprotect() from elevating later on
file_flags &= ~kNtFileMapExecute;
switch (page_flags) {
case kNtPageExecuteWritecopy:
page_flags = kNtPageWritecopy;
break;
case kNtPageExecuteReadwrite:
page_flags = kNtPageReadwrite;
break;
case kNtPageExecuteRead:
page_flags = kNtPageReadonly;
break;
default:
__builtin_unreachable();
}
errno = e;
goto TryAgain;
}
dm.hand = kNtInvalidHandleValue;
dm.addr = (void *)(intptr_t)-1;
return dm;
}
static struct DirectMap sys_mmap(void *addr, size_t size, int prot, int flags,
int fd, int64_t off) {
struct DirectMap d;
if (IsXnuSilicon()) {
long p = _sysret(__syslib->__mmap(addr, size, prot, flags, fd, off));
d.hand = kNtInvalidHandleValue;
d.addr = (void *)p;
} else if (IsWindows()) {
d = sys_mmap_nt(addr, size, prot, flags, fd, off);
} else if (IsMetal()) {
d.addr = sys_mmap_metal(addr, size, prot, flags, fd, off);
d.hand = kNtInvalidHandleValue;
} else {
d.addr = __sys_mmap(addr, size, prot, flags, fd, off, off);
d.hand = kNtInvalidHandleValue;
}
return d;
}
struct Map *__maps_alloc(void) {
struct Map *map;
uintptr_t tip = atomic_load_explicit(&__maps.freed, memory_order_relaxed);
@ -467,7 +596,7 @@ struct Map *__maps_alloc(void) {
if (sys.addr == MAP_FAILED)
return 0;
if (IsWindows())
CloseHandle(sys.maphandle);
CloseHandle(sys.hand);
struct MapSlab *slab = sys.addr;
while (!atomic_compare_exchange_weak(&__maps.slabs, &slab->next, slab)) {
}
@ -717,7 +846,7 @@ static void *__mmap_impl(char *addr, size_t size, int prot, int flags, int fd,
map->off = off;
map->prot = prot;
map->flags = flags;
map->hand = res.maphandle;
map->hand = res.hand;
if (IsWindows()) {
map->iscow = (flags & MAP_TYPE) != MAP_SHARED && fd != -1;
map->readonlyfile = (flags & MAP_TYPE) == MAP_SHARED && fd != -1 &&