ffitarget.h

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Hash : 9ba55921
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Date : 2021-03-05T10:07:30

Static tramp v5 (#624) * Static Trampolines Closure Trampoline Security Issue ================================= Currently, the trampoline code used in libffi is not statically defined in a source file (except for MACH). The trampoline is either pre-defined machine code in a data buffer. Or, it is generated at runtime. In order to execute a trampoline, it needs to be placed in a page with executable permissions. Executable data pages are attack surfaces for attackers who may try to inject their own code into the page and contrive to have it executed. The security settings in a system may prevent various tricks used in user land to write code into a page and to have it executed somehow. On such systems, libffi trampolines would not be able to run. Static Trampoline ================= To solve this problem, the trampoline code needs to be defined statically in a source file, compiled and placed in the text segment so it can be mapped and executed naturally without any tricks. However, the trampoline needs to be able to access the closure pointer at runtime. PC-relative data referencing ============================ The solution implemented in this patch set uses PC-relative data references. The trampoline is mapped in a code page. Adjacent to the code page, a data page is mapped that contains the parameters of the trampoline: - the closure pointer - pointer to the ABI handler to jump to The trampoline code uses an offset relative to its current PC to access its data. Some architectures support PC-relative data references in the ISA itself. E.g., X64 supports RIP-relative references. For others, the PC has to somehow be loaded into a general purpose register to do PC-relative data referencing. To do this, we need to define a get_pc() kind of function and call it to load the PC in a desired register. There are two cases: 1. The call instruction pushes the return address on the stack. In this case, get_pc() will extract the return address from the stack and load it in the desired register and return. 2. The call instruction stores the return address in a designated register. In this case, get_pc() will copy the return address to the desired register and return. Either way, the PC next to the call instruction is obtained. Scratch register ================ In order to do its job, the trampoline code would need to use a scratch register. Depending on the ABI, there may not be a register available for scratch. This problem needs to be solved so that all ABIs will work. The trampoline will save two values on the stack: - the closure pointer - the original value of the scratch register This is what the stack will look like: sp before trampoline ------> -------------------- | closure pointer | -------------------- | scratch register | sp after trampoline -------> -------------------- The ABI handler can do the following as needed by the ABI: - the closure pointer can be loaded in a desired register - the scratch register can be restored to its original value - the stack pointer can be restored to its original value (the value when the trampoline was invoked) To do this, I have defined prolog code for each ABI handler. The legacy trampoline jumps to the ABI handler directly. But the static trampoline defined in this patch jumps tp the prolog code which performs the above actions before jumping to the ABI handler. Trampoline Table ================ In order to reduce the trampoline memory footprint, the trampoline code would be defined as a code array in the text segment. This array would be mapped into the address space of the caller. The mapping would, therefore, contain a trampoline table. Adjacent to the trampoline table mapping, there will be a data mapping that contains a parameter table, one parameter block for each trampoline. The parameter block will contain: - a pointer to the closure - a pointer to the ABI handler The static trampoline code would finally look like this: - Make space on the stack for the closure and the scratch register by moving the stack pointer down - Store the original value of the scratch register on the stack - Using PC-relative reference, get the closure pointer - Store the closure pointer on the stack - Using PC-relative reference, get the ABI handler pointer - Jump to the ABI handler Mapping size ============ The size of the code mapping that contains the trampoline table needs to be determined on a per architecture basis. If a particular architecture supports multiple base page sizes, then the largest supported base page size needs to be chosen. E.g., we choose 16K for ARM64. Trampoline allocation and free ============================== Static trampolines are allocated in ffi_closure_alloc() and freed in ffi_closure_free(). Normally, applications use these functions. But there are some cases out there where the user of libffi allocates and manages its own closure memory. In such cases, static trampolines cannot be used. These will fall back to using legacy trampolines. The user has to make sure that the memory is executable. ffi_closure structure ===================== I did not want to make any changes to the size of the closure structure for this feature to guarantee compatibility. But the opaque static trampoline handle needs to be stored in the closure. I have defined it as follows: - char tramp[FFI_TRAMPOLINE_SIZE]; + union { + char tramp[FFI_TRAMPOLINE_SIZE]; + void *ftramp; + }; If static trampolines are used, then tramp[] is not needed to store a dynamic trampoline. That space can be reused to store the handle. Hence, the union. Architecture Support ==================== Support has been added for x64, i386, aarch64 and arm. Support for other architectures can be added very easily in the future. OS Support ========== Support has been added for Linux. Support for other OSes can be added very easily. Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> * x86: Support for Static Trampolines - Define the arch-specific initialization function ffi_tramp_arch () that returns trampoline size information to common code. - Define the trampoline code mapping and data mapping sizes. - Define the trampoline code table statically. Define two tables, actually, one with CET and one without. - Introduce a tiny prolog for each ABI handling function. The ABI handlers addressed are: - ffi_closure_unix64 - ffi_closure_unix64_sse - ffi_closure_win64 The prolog functions are called: - ffi_closure_unix64_alt - ffi_closure_unix64_sse_alt - ffi_closure_win64_alt The legacy trampoline jumps to the ABI handler. The static trampoline jumps to the prolog function. The prolog function uses the information provided by the static trampoline, sets things up for the ABI handler and then jumps to the ABI handler. - Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to initialize static trampoline parameters. Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> * i386: Support for Static Trampolines - Define the arch-specific initialization function ffi_tramp_arch () that returns trampoline size information to common code. - Define the trampoline code table statically. Define two tables, actually, one with CET and one without. - Define the trampoline code table statically. - Introduce a tiny prolog for each ABI handling function. The ABI handlers addressed are: - ffi_closure_i386 - ffi_closure_STDCALL - ffi_closure_REGISTER The prolog functions are called: - ffi_closure_i386_alt - ffi_closure_STDCALL_alt - ffi_closure_REGISTER_alt The legacy trampoline jumps to the ABI handler. The static trampoline jumps to the prolog function. The prolog function uses the information provided by the static trampoline, sets things up for the ABI handler and then jumps to the ABI handler. - Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to initialize static trampoline parameters. Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> * arm64: Support for Static Trampolines - Define the arch-specific initialization function ffi_tramp_arch () that returns trampoline size information to common code. - Define the trampoline code mapping and data mapping sizes. - Define the trampoline code table statically. - Introduce a tiny prolog for each ABI handling function. The ABI handlers addressed are: - ffi_closure_SYSV - ffi_closure_SYSV_V The prolog functions are called: - ffi_closure_SYSV_alt - ffi_closure_SYSV_V_alt The legacy trampoline jumps to the ABI handler. The static trampoline jumps to the prolog function. The prolog function uses the information provided by the static trampoline, sets things up for the ABI handler and then jumps to the ABI handler. - Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to initialize static trampoline parameters. Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com> * arm: Support for Static Trampolines - Define the arch-specific initialization function ffi_tramp_arch () that returns trampoline size information to common code. - Define the trampoline code mapping and data mapping sizes. - Define the trampoline code table statically. - Introduce a tiny prolog for each ABI handling function. The ABI handlers addressed are: - ffi_closure_SYSV - ffi_closure_VFP The prolog functions are called: - ffi_closure_SYSV_alt - ffi_closure_VFP_alt The legacy trampoline jumps to the ABI handler. The static trampoline jumps to the prolog function. The prolog function uses the information provided by the static trampoline, sets things up for the ABI handler and then jumps to the ABI handler. - Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to initialize static trampoline parameters. Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>

src/x86/ffitarget.h

/* -----------------------------------------------------------------*-C-*-
   ffitarget.h - Copyright (c) 2012, 2014, 2018  Anthony Green
                 Copyright (c) 1996-2003, 2010  Red Hat, Inc.
                 Copyright (C) 2008  Free Software Foundation, Inc.

   Target configuration macros for x86 and x86-64.

   Permission is hereby granted, free of charge, to any person obtaining
   a copy of this software and associated documentation files (the
   ``Software''), to deal in the Software without restriction, including
   without limitation the rights to use, copy, modify, merge, publish,
   distribute, sublicense, and/or sell copies of the Software, and to
   permit persons to whom the Software is furnished to do so, subject to
   the following conditions:

   The above copyright notice and this permission notice shall be included
   in all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND,
   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
   DEALINGS IN THE SOFTWARE.

   ----------------------------------------------------------------------- */

#ifndef LIBFFI_TARGET_H
#define LIBFFI_TARGET_H

#ifndef LIBFFI_H
#error "Please do not include ffitarget.h directly into your source.  Use ffi.h instead."
#endif

/* ---- System specific configurations ----------------------------------- */

/* For code common to all platforms on x86 and x86_64. */
#define X86_ANY

#if defined (X86_64) && defined (__i386__)
#undef X86_64
#define X86
#endif

#ifdef X86_WIN64
#define FFI_SIZEOF_ARG 8
#define USE_BUILTIN_FFS 0 /* not yet implemented in mingw-64 */
#endif

#define FFI_TARGET_SPECIFIC_STACK_SPACE_ALLOCATION
#ifndef _MSC_VER
#define FFI_TARGET_HAS_COMPLEX_TYPE
#endif

/* ---- Generic type definitions ----------------------------------------- */

#ifndef LIBFFI_ASM
#ifdef X86_WIN64
#ifdef _MSC_VER
typedef unsigned __int64       ffi_arg;
typedef __int64                ffi_sarg;
#else
typedef unsigned long long     ffi_arg;
typedef long long              ffi_sarg;
#endif
#else
#if defined __x86_64__ && defined __ILP32__
#define FFI_SIZEOF_ARG 8
#define FFI_SIZEOF_JAVA_RAW  4
typedef unsigned long long     ffi_arg;
typedef long long              ffi_sarg;
#else
typedef unsigned long          ffi_arg;
typedef signed long            ffi_sarg;
#endif
#endif

typedef enum ffi_abi {
#if defined(X86_WIN64)
  FFI_FIRST_ABI = 0,
  FFI_WIN64,            /* sizeof(long double) == 8  - microsoft compilers */
  FFI_GNUW64,           /* sizeof(long double) == 16 - GNU compilers */
  FFI_LAST_ABI,
#ifdef __GNUC__
  FFI_DEFAULT_ABI = FFI_GNUW64
#else  
  FFI_DEFAULT_ABI = FFI_WIN64
#endif  

#elif defined(X86_64) || (defined (__x86_64__) && defined (X86_DARWIN))
  FFI_FIRST_ABI = 1,
  FFI_UNIX64,
  FFI_WIN64,
  FFI_EFI64 = FFI_WIN64,
  FFI_GNUW64,
  FFI_LAST_ABI,
  FFI_DEFAULT_ABI = FFI_UNIX64

#elif defined(X86_WIN32)
  FFI_FIRST_ABI = 0,
  FFI_SYSV      = 1,
  FFI_STDCALL   = 2,
  FFI_THISCALL  = 3,
  FFI_FASTCALL  = 4,
  FFI_MS_CDECL  = 5,
  FFI_PASCAL    = 6,
  FFI_REGISTER  = 7,
  FFI_LAST_ABI,
  FFI_DEFAULT_ABI = FFI_MS_CDECL
#else
  FFI_FIRST_ABI = 0,
  FFI_SYSV      = 1,
  FFI_THISCALL  = 3,
  FFI_FASTCALL  = 4,
  FFI_STDCALL   = 5,
  FFI_PASCAL    = 6,
  FFI_REGISTER  = 7,
  FFI_MS_CDECL  = 8,
  FFI_LAST_ABI,
  FFI_DEFAULT_ABI = FFI_SYSV
#endif
} ffi_abi;
#endif

/* ---- Definitions for closures ----------------------------------------- */

#define FFI_CLOSURES 1
#define FFI_GO_CLOSURES 1

#define FFI_TYPE_SMALL_STRUCT_1B (FFI_TYPE_LAST + 1)
#define FFI_TYPE_SMALL_STRUCT_2B (FFI_TYPE_LAST + 2)
#define FFI_TYPE_SMALL_STRUCT_4B (FFI_TYPE_LAST + 3)
#define FFI_TYPE_MS_STRUCT       (FFI_TYPE_LAST + 4)

#if defined (X86_64) || defined(X86_WIN64) \
    || (defined (__x86_64__) && defined (X86_DARWIN))
/* 4 bytes of ENDBR64 + 7 bytes of LEA + 6 bytes of JMP + 7 bytes of NOP
   + 8 bytes of pointer.  */
# define FFI_TRAMPOLINE_SIZE 32
# define FFI_NATIVE_RAW_API 0
#else
/* 4 bytes of ENDBR32 + 5 bytes of MOV + 5 bytes of JMP + 2 unused
   bytes.  */
# define FFI_TRAMPOLINE_SIZE 16
# define FFI_NATIVE_RAW_API 1  /* x86 has native raw api support */
#endif

#if !defined(GENERATE_LIBFFI_MAP) && defined(__CET__)
# include <cet.h>
# if (__CET__ & 1) != 0
#   define ENDBR_PRESENT
# endif
# define _CET_NOTRACK notrack
#else
# define _CET_ENDBR
# define _CET_NOTRACK
#endif

#endif

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