8000 [RFC WIP] Apple whole dylib trampoline by jeremyhu · Pull Request #621 · libffi/libffi · GitHub
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[RFC WIP] Apple whole dylib trampoline #621

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[RFC WIP] Apple whole dylib trampoline #621

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5 changes: 5 additions & 0 deletions include/ffi.h.in
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Original file line number Diff line number Diff line change
Expand Up @@ -362,6 +362,11 @@ ffi_prep_closure_loc (ffi_closure*,
void *user_data,
void*codeloc);

#if defined(__x86_64__) || defined(__arm64__)
FFI_API ffi_closure *
ffi_find_closure_for_code(void *code);
#endif

#ifdef __sgi
# pragma pack 8
#endif
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20 changes: 20 additions & 0 deletions src/aarch64/ffi.c
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Expand Up @@ -813,7 +813,11 @@ ffi_prep_closure_loc (ffi_closure *closure,
#ifdef HAVE_PTRAUTH
codeloc = ptrauth_auth_data(codeloc, ptrauth_key_function_pointer, 0);
#endif
#ifdef FFI_TRAMPOLINE_WHOLE_DYLIB
void **config = (void **)((uint8_t *)codeloc - 2*PAGE_MAX_SIZE);
#else
void **config = (void **)((uint8_t *)codeloc - PAGE_MAX_SIZE);
#endif
config[0] = closure;
config[1] = start;
#endif
Expand Down Expand Up @@ -864,6 +868,22 @@ ffi_prep_closure_loc (ffi_closure *closure,
return FFI_OK;
}

ffi_closure *
ffi_find_closure_for_code(void *codeloc)
{
#if FFI_EXEC_TRAMPOLINE_TABLE
# ifdef FFI_TRAMPOLINE_WHOLE_DYLIB
void **config = (void **)((uint8_t *)codeloc - 2*PAGE_MAX_SIZE);
# else
void **config = (void **)((uint8_t *)codeloc - PAGE_MAX_SIZE);
# endif
return config[0];
#else
return (ffi_closure*)codeloc;
#endif
}


#ifdef FFI_GO_CLOSURES
extern void ffi_go_closure_SYSV (void) FFI_HIDDEN;
extern void ffi_go_closure_SYSV_V (void) FFI_HIDDEN;
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44 changes: 44 additions & 0 deletions src/aarch64/trampoline.S
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@@ -0,0 +1,44 @@
#ifdef __arm64__

#define LIBFFI_ASM
#include <fficonfig.h>
#include <ffi.h>
#include <ffi_cfi.h>
#include "internal.h"

#ifdef FFI_EXEC_TRAMPOLINE_TABLE

#ifdef __MACH__
#include <mach/machine/vm_param.h>
#endif

#ifdef HAVE_MACHINE_ASM_H
# include <machine/asm.h>
#else
# ifdef __USER_LABEL_PREFIX__
# define CONCAT1(a, b) CONCAT2(a, b)
# define CONCAT2(a, b) a ## b
# define CNAME(x) CONCAT1 (__USER_LABEL_PREFIX__, x)
# else
# define CNAME(x) x
# endif
#endif

.set page_max_size, PAGE_MAX_SIZE
.align PAGE_MAX_SHIFT
.text
.globl CNAME(ffi_closure_trampoline_table_page)
CNAME(ffi_closure_trampoline_table_page):
.rept PAGE_MAX_SIZE / FFI_TRAMPOLINE_SIZE
#ifdef FFI_TRAMPOLINE_WHOLE_DYLIB
adr x16, -(2 * PAGE_MAX_SIZE)
#else
adr x16, -PAGE_MAX_SIZE
#endif
ldp x17, x16, [x16]
BRANCH_TO_REG x16
nop /* each entry in the trampoline config page is 2*sizeof(void*) so the trampoline itself cannot be smaller that 16 bytes */
.endr

#endif /* FFI_EXEC_TRAMPOLINE_TABLE */
#endif /* __arm64__ */
67 changes: 58 additions & 9 deletions src/closures.c
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Expand Up @@ -164,7 +164,13 @@ ffi_tramp_is_present (__attribute__((unused)) void *ptr)
#include <stdio.h>
#include <stdlib.h>

#ifdef FFI_TRAMPOLINE_WHOLE_DYLIB
#include <assert.h>
#include <dispatch/dispatch.h>
#include <dlfcn.h>
#else
extern void *ffi_closure_trampoline_table_page;
#endif

typedef struct ffi_trampoline_table ffi_trampoline_table;
typedef struct ffi_trampoline_table_entry ffi_trampoline_table_entry;
Expand Down Expand Up @@ -192,6 +198,21 @@ struct ffi_trampoline_table_entry
/* Total number of trampolines that fit in one trampoline table */
#define FFI_TRAMPOLINE_COUNT (PAGE_MAX_SIZE / FFI_TRAMPOLINE_SIZE)

/* The trampoline dylib has one page for the MACHO_HEADER and one page for the
* trampolines. iOS 12.0 and later, and macOS on Apple Silicon require that
* the entire dylib needs to be remapped as a unit.
*
* arm (legacy): Allocate two pages -- a config page and a placeholder for the trampolines
* arm64 (modern): Allocate three pages -- a config page and two placeholders for the trampoline dylib
*/
#ifdef FFI_TRAMPOLINE_WHOLE_DYLIB
#define FFI_TRAMPOLINE_ALLOCATION_PAGE_COUNT 3
#define FFI_TRAMPOLINE_PAGE_SEGMENT_OFFSET PAGE_MAX_SIZE
#else
#define FFI_TRAMPOLINE_ALLOCATION_PAGE_COUNT 2
#define FFI_TRAMPOLINE_PAGE_SEGMENT_OFFSET 0
#endif

static pthread_mutex_t ffi_trampoline_lock = PTHREAD_MUTEX_INITIALIZER;
static ffi_trampoline_table *ffi_trampoline_tables = NULL;

Expand All @@ -207,35 +228,63 @@ ffi_trampoline_table_alloc (void)
kern_return_t kt;
uint16_t i;

/* Allocate two pages -- a config page and a placeholder page */
config_page = 0x0;
kt = vm_allocate (mach_task_self (), &config_page, PAGE_MAX_SIZE * 2,
/* The entire allocation is:
* config_page
* trampoline_segment
*
* trampoline_segment is:
* trampoline dylib mach-o header (if FFI_TRAMPOLINE_WHOLE_DYLIB)
* trampoline page
*/
kt = vm_allocate (mach_task_self (), &config_page, FFI_TRAMPOLINE_ALLOCATION_PAGE_COUNT * PAGE_MAX_SIZE,
VM_FLAGS_ANYWHERE);
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Note that ffi_trampoline_table_free() needs to be updated to avoid leaking memory, as it deallocates PAGE_MAX_SIZE * 2.

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@oleavr oleavr Aug 25, 2022 •
edited
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@jeremyhu Just took a quick look at ffi_closure_free() on macOS 12.5 using r2, and macOS' libffi does indeed have this memory leak:

Screenshot 2022-08-25 at 20 53 46

if (kt != KERN_SUCCESS)
return NULL;

/* Remap the trampoline table on top of the placeholder page */
trampoline_page = config_page + PAGE_MAX_SIZE;
static void *trampoline_table_page;

#ifdef FFI_TRAMPOLINE_WHOLE_DYLIB
static dispatch_once_t trampoline_template_init_once;

dispatch_once(&trampoline_template_init_once, ^{
void * const trampoline_handle = dlopen("/usr/lib/libffi-trampolines.dylib", RTLD_NOW | RTLD_LOCAL | RTLD_FIRST);
assert(trampoline_handle);

trampoline_table_page = dlsym(trampoline_handle, "ffi_closure_trampoline_table_page");
assert(trampoline_table_page);
});
#else
trampoline_table_page = &ffi_closure_trampoline_table_page;
#endif

#ifdef HAVE_PTRAUTH
trampoline_page_template = (vm_address_t)(uintptr_t)ptrauth_auth_data((void *)&ffi_closure_trampoline_table_page, ptrauth_key_function_pointer, 0);
trampoline_page_template = (uintptr_t)ptrauth_auth_data(trampoline_table_page, ptrauth_key_function_pointer, 0);
#else
trampoline_page_template = (vm_address_t)&ffi_closure_trampoline_table_page;
trampoline_page_template = (uintptr_t)trampoline_table_page;
#endif

#ifdef __arm__
/* ffi_closure_trampoline_table_page can be thumb-biased on some ARM archs */
trampoline_page_template &= ~1UL;
#endif
kt = vm_remap (mach_task_self (), &trampoline_page, PAGE_MAX_SIZE, 0x0,
VM_FLAGS_OVERWRITE, mach_task_self (), trampoline_page_template,

vm_address_t trampoline_segment_template = trampoline_page_template - FFI_TRAMPOLINE_PAGE_SEGMENT_OFFSET;
vm_size_t trampoline_segment_size = (FFI_TRAMPOLINE_ALLOCATION_PAGE_COUNT - 1) * PAGE_MAX_SIZE;

/* Remap the trampoline table on top of the placeholder page */
vm_address_t trampoline_segment = config_page + PAGE_MAX_SIZE;
kt = vm_remap (mach_task_self(), &trampoline_segment, trampoline_segment_size, 0x0,
VM_FLAGS_FIXED | VM_FLAGS_OVERWRITE, mach_task_self(), trampoline_segment_template,
FALSE, &cur_prot, &max_prot, VM_INHERIT_SHARE);
if (kt != KERN_SUCCESS || !(cur_prot & VM_PROT_EXECUTE))
{
vm_deallocate (mach_task_self (), config_page, PAGE_MAX_SIZE * 2);
vm_deallocate (mach_task_self (), config_page, FFI_TRAMPOLINE_ALLOCATION_PAGE_COUNT * PAGE_MAX_SIZE);
return NULL;
}

trampoline_page = trampoline_segment + FFI_TRAMPOLINE_PAGE_SEGMENT_OFFSET;

/* We have valid trampoline and config pages */
table = calloc (1, sizeof (ffi_trampoline_table));
table->free_count = FFI_TRAMPOLINE_COUNT;
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6 changes: 6 additions & 0 deletions src/x86/ffi64.c
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Expand Up @@ -788,6 +788,12 @@ ffi_prep_closure_loc (ffi_closure* closure,
return FFI_OK;
}

ffi_closure *
ffi_find_closure_for_code(void *code)
{
return (ffi_closure *) code;
}

int FFI_HIDDEN
ffi_closure_unix64_inner(ffi_cif *cif,
void (*fun)(ffi_cif*, void*, void**, void*),
Expand Down
0