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liblzma: Remove ifunc support. 

This is *NOT* done for security reasons even though the backdoor
relied on the ifunc code. Instead, the reason is that in this
project ifunc provides little benefits but it's quite a bit of
extra code to support it. The only case where ifunc *might* matter
for performance is if the CRC functions are used directly by an
application. In normal compression use it's completely irrelevant.
This commit is contained in:
Lasse Collin 2024-04-09 17:43:16 +03:00
parent 6b4c859059
commit 689ae24273
7 changed files with 8 additions and 247 deletions
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79
CMakeLists.txt
View File

@ -1099,85 +1099,6 @@ if(USE_WIN95_THREADS AND ENABLE_SMALL AND NOT HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR)
endif() endif()
# Check for __attribute__((__ifunc__())) support.
# Supported values for USE_ATTR_IFUNC:
#
# auto (default) - Detect ifunc support with a compile test.
# ON - Always enable ifunc.
# OFF - Disable ifunc usage.
set(USE_ATTR_IFUNC "auto" CACHE STRING "Use __attribute__((__ifunc__())).")
set(SUPPORTED_USE_ATTR_IFUNC auto ON OFF)
if(NOT USE_ATTR_IFUNC IN_LIST SUPPORTED_USE_ATTR_IFUNC)
message(FATAL_ERROR "'${USE_ATTR_IFUNC}' is not a supported value for"
"USE_ATTR_IFUNC")
endif()
# When USE_ATTR_IFUNC is 'auto', allow the use of __attribute__((__ifunc__()))
# if compiler support is detected and we are building for GNU/Linux (glibc)
# or FreeBSD. uClibc and musl don't support ifunc in their dynamic linkers
# but some compilers still accept the attribute when compiling for these
# C libraries, which results in broken binaries. That's why we need to
# check which libc is being used.
if(USE_ATTR_IFUNC STREQUAL "auto")
cmake_push_check_state()
set(CMAKE_REQUIRED_FLAGS "-Werror")
check_c_source_compiles("
/*
* Force a compilation error when not using glibc on Linux
* or if we are not using FreeBSD. uClibc will define
* __GLIBC__ but does not support ifunc, so we must have
* an extra check to disable with uClibc.
*/
#if defined(__linux__)
# include <features.h>
# if !defined(__GLIBC__) || defined(__UCLIBC__)
compile error
# endif
#elif !defined(__FreeBSD__)
compile error
#endif
static void func(void) { return; }
/*
* The attribute __no_profile_instrument_function__ is
* needed with GCC to prevent improper instrumentation in
* the ifunc resolver.
*/
__attribute__((__no_profile_instrument_function__))
static void (*resolve_func(void)) (void) { return func; }
void func_ifunc(void)
__attribute__((__ifunc__(\"resolve_func\")));
int main(void) { return 0; }
/*
* 'clang -Wall' incorrectly warns that resolve_func is
* unused (-Wunused-function). Correct assembly output is
* still produced. This problem exists at least in Clang
* versions 4 to 17. The following silences the bogus warning:
*/
void make_clang_quiet(void);
void make_clang_quiet(void) { resolve_func()(); }
"
SYSTEM_SUPPORTS_IFUNC)
cmake_pop_check_state()
endif()
if(USE_ATTR_IFUNC STREQUAL "ON" OR SYSTEM_SUPPORTS_IFUNC)
tuklib_add_definitions(liblzma HAVE_FUNC_ATTRIBUTE_IFUNC)
if(CMAKE_C_FLAGS MATCHES "-fsanitize=")
message(SEND_ERROR
"CMAKE_C_FLAGS or the environment variable CFLAGS "
"contains '-fsanitize=' which is incompatible "
"with ifunc. Use -DUSE_ATTR_IFUNC=OFF "
"as an argument to 'cmake' when using '-fsanitize'.")
endif()
endif()
# cpuid.h # cpuid.h
check_include_file(cpuid.h HAVE_CPUID_H) check_include_file(cpuid.h HAVE_CPUID_H)
tuklib_add_definition_if(liblzma HAVE_CPUID_H) tuklib_add_definition_if(liblzma HAVE_CPUID_H)

8
INSTALL
View File

@ -518,14 +518,6 @@ XZ Utils Installation
calls any liblzma functions from more than calls any liblzma functions from more than
one thread, something bad may happen. one thread, something bad may happen.
--enable-ifunc
Use __attribute__((__ifunc__())) in liblzma. This is
enabled by default on GNU/Linux and FreeBSD.
The ifunc attribute is incompatible with
-fsanitize=address. --disable-ifunc must be used
if any -fsanitize= option is specified in CFLAGS.
--enable-sandbox=METHOD --enable-sandbox=METHOD
There is limited sandboxing support in the xz and xzdec There is limited sandboxing support in the xz and xzdec
tools. If built with sandbox support, xz uses it tools. If built with sandbox support, xz uses it

79
configure.ac
View File

@ -893,85 +893,6 @@ if test "x$enable_small$enable_threads$have_func_attribute_constructor" \
__attribute__((__constructor__))]) __attribute__((__constructor__))])
fi fi
# __attribute__((__ifunc__())) can be used to choose between different
# implementations of the same function at runtime. This is slightly more
# efficient than using __attribute__((__constructor__)) and setting
# a function pointer.
AC_ARG_ENABLE([ifunc], [AS_HELP_STRING([--enable-ifunc],
[Use __attribute__((__ifunc__())). Enabled by default on
GNU/Linux (glibc) and FreeBSD.])],
[], [enable_ifunc=auto])
# When enable_ifunc is 'auto', allow the use of __attribute__((__ifunc__()))
# if compiler support is detected and we are building for GNU/Linux (glibc)
# or FreeBSD. uClibc and musl don't support ifunc in their dynamic linkers
# but some compilers still accept the attribute when compiling for these
# C libraries, which results in broken binaries. That's why we need to
# check which libc is being used.
if test "x$enable_ifunc" = xauto ; then
OLD_CFLAGS="$CFLAGS"
CFLAGS="$CFLAGS -Werror"
AC_MSG_CHECKING([if __attribute__((__ifunc__())) can be used])
AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
/*
* Force a compilation error when not using glibc on Linux
* or if we are not using FreeBSD. uClibc will define
* __GLIBC__ but does not support ifunc, so we must have
* an extra check to disable with uClibc.
*/
#if defined(__linux__)
# include <features.h>
# if !defined(__GLIBC__) || defined(__UCLIBC__)
compile error
# endif
#elif !defined(__FreeBSD__)
compile error
#endif
static void func(void) { return; }
/*
* The attribute __no_profile_instrument_function__ is
* needed with GCC to prevent improper instrumentation in
* the ifunc resolver.
*/
__attribute__((__no_profile_instrument_function__))
static void (*resolve_func (void)) (void) { return func; }
void func_ifunc (void)
__attribute__((__ifunc__("resolve_func")));
/*
* 'clang -Wall' incorrectly warns that resolve_func is
* unused (-Wunused-function). Correct assembly output is
* still produced. This problem exists at least in Clang
* versions 4 to 17. The following silences the bogus warning:
*/
void make_clang_quiet(void);
void make_clang_quiet(void) { resolve_func()(); }
]])], [
enable_ifunc=yes
], [
enable_ifunc=no
])
AC_MSG_RESULT([$enable_ifunc])
CFLAGS="$OLD_CFLAGS"
fi
if test "x$enable_ifunc" = xyes ; then
AC_DEFINE([HAVE_FUNC_ATTRIBUTE_IFUNC], [1],
[Define to 1 if __attribute__((__ifunc__()))
is supported for functions.])
# ifunc explicitly does not work with -fsanitize=address.
# If configured, it will result in a liblzma build that will fail
# when liblzma is loaded at runtime (when the ifunc resolver
# executes).
AS_CASE([$CFLAGS], [*-fsanitize=*], [AC_MSG_ERROR([
CFLAGS contains '-fsanitize=' which is incompatible with ifunc.
Use --disable-ifunc when using '-fsanitize'.])])
fi
############################################################################### ###############################################################################
# Checks for library functions. # Checks for library functions.

48
src/liblzma/check/crc32_fast.c
View File

@ -97,24 +97,14 @@ crc32_generic(const uint8_t *buf, size_t size, uint32_t crc)
// If both the generic and arch-optimized implementations are built, then // If both the generic and arch-optimized implementations are built, then
// the function to use is selected at runtime because the system running // the function to use is selected at runtime because the system running
// the binary might not have the arch-specific instruction set extension(s) // the binary might not have the arch-specific instruction set extension(s)
// available. The three dispatch methods in order of priority: // available. The dispatch methods in order of priority:
// //
// 1. Indirect function (ifunc). This method is slightly more efficient // 1. Constructor. This method uses __attribute__((__constructor__)) to
// than the constructor method because it will change the entry in the
// Procedure Linkage Table (PLT) for the function either at load time or
// at the first call. This avoids having to call the function through a
// function pointer and will treat the function call like a regular call
// through the PLT. ifuncs are created by using
// __attribute__((__ifunc__("resolver"))) on a function which has no
// body. The "resolver" is the name of the function that chooses at
// runtime which implementation to use.
//
// 2. Constructor. This method uses __attribute__((__constructor__)) to
// set crc32_func at load time. This avoids extra computation (and any // set crc32_func at load time. This avoids extra computation (and any
// unlikely threading bugs) on the first call to lzma_crc32() to decide // unlikely threading bugs) on the first call to lzma_crc32() to decide
// which implementation should be used. // which implementation should be used.
// //
// 3. First Call Resolution. On the very first call to lzma_crc32(), the // 2. First Call Resolution. On the very first call to lzma_crc32(), the
// call will be directed to crc32_dispatch() instead. This will set the // call will be directed to crc32_dispatch() instead. This will set the
// appropriate implementation function and will not be called again. // appropriate implementation function and will not be called again.
// This method does not use any kind of locking but is safe because if // This method does not use any kind of locking but is safe because if
@ -124,22 +114,7 @@ crc32_generic(const uint8_t *buf, size_t size, uint32_t crc)
typedef uint32_t (*crc32_func_type)( typedef uint32_t (*crc32_func_type)(
const uint8_t *buf, size_t size, uint32_t crc); const uint8_t *buf, size_t size, uint32_t crc);
// Clang 16.0.0 and older has a bug where it marks the ifunc resolver // This resolver is shared between all dispatch methods.
// function as unused since it is static and never used outside of
// __attribute__((__ifunc__())).
#if defined(CRC_USE_IFUNC) && defined(__clang__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wunused-function"
#endif
// This resolver is shared between all three dispatch methods. It serves as
// the ifunc resolver if ifunc is supported, otherwise it is called as a
// regular function by the constructor or first call resolution methods.
// The __no_profile_instrument_function__ attribute support is checked when
// determining if ifunc can be used, so it is safe to use here.
#ifdef CRC_USE_IFUNC
__attribute__((__no_profile_instrument_function__))
#endif
static crc32_func_type static crc32_func_type
crc32_resolve(void) crc32_resolve(void)
{ {
@ -147,11 +122,6 @@ crc32_resolve(void)
? &crc32_arch_optimized : &crc32_generic; ? &crc32_arch_optimized : &crc32_generic;
} }
#if defined(CRC_USE_IFUNC) && defined(__clang__)
# pragma GCC diagnostic pop
#endif
#ifndef CRC_USE_IFUNC
#ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR #ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
// Constructor method. // Constructor method.
@ -176,8 +146,7 @@ crc32_set_func(void)
static uint32_t static uint32_t
crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc) crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc)
{ {
// When __attribute__((__ifunc__(...))) and // When __attribute__((__constructor__)) isn't supported, set the
// __attribute__((__constructor__)) isn't supported, set the
// function pointer without any locking. If multiple threads run // function pointer without any locking. If multiple threads run
// the detection code in parallel, they will all end up setting // the detection code in parallel, they will all end up setting
// the pointer to the same value. This avoids the use of // the pointer to the same value. This avoids the use of
@ -189,14 +158,8 @@ crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc)
#endif #endif
#endif #endif
#endif
#ifdef CRC_USE_IFUNC
extern LZMA_API(uint32_t)
lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
__attribute__((__ifunc__("crc32_resolve")));
#else
extern LZMA_API(uint32_t) extern LZMA_API(uint32_t)
lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc) lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
{ {
@ -239,4 +202,3 @@ lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
return crc32_generic(buf, size, crc); return crc32_generic(buf, size, crc);
#endif #endif
} }
#endif

21
src/liblzma/check/crc64_fast.c
View File

@ -93,14 +93,6 @@ crc64_generic(const uint8_t *buf, size_t size, uint64_t crc)
typedef uint64_t (*crc64_func_type)( typedef uint64_t (*crc64_func_type)(
const uint8_t *buf, size_t size, uint64_t crc); const uint8_t *buf, size_t size, uint64_t crc);
#if defined(CRC_USE_IFUNC) && defined(__clang__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wunused-function"
#endif
#ifdef CRC_USE_IFUNC
__attribute__((__no_profile_instrument_function__))
#endif
static crc64_func_type static crc64_func_type
crc64_resolve(void) crc64_resolve(void)
{ {
@ -108,12 +100,6 @@ crc64_resolve(void)
? &crc64_arch_optimized : &crc64_generic; ? &crc64_arch_optimized : &crc64_generic;
} }
#if defined(CRC_USE_IFUNC) && defined(__clang__)
# pragma GCC diagnostic pop
#endif
#ifndef CRC_USE_IFUNC
#ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR #ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
# define CRC64_SET_FUNC_ATTR __attribute__((__constructor__)) # define CRC64_SET_FUNC_ATTR __attribute__((__constructor__))
static crc64_func_type crc64_func; static crc64_func_type crc64_func;
@ -142,14 +128,8 @@ crc64_dispatch(const uint8_t *buf, size_t size, uint64_t crc)
} }
#endif #endif
#endif #endif
#endif
#ifdef CRC_USE_IFUNC
extern LZMA_API(uint64_t)
lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
__attribute__((__ifunc__("crc64_resolve")));
#else
extern LZMA_API(uint64_t) extern LZMA_API(uint64_t)
lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc) lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
{ {
@ -174,4 +154,3 @@ lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
return crc64_generic(buf, size, crc); return crc64_generic(buf, size, crc);
#endif #endif
} }
#endif

9
src/liblzma/check/crc_common.h
View File

@ -67,8 +67,6 @@
#undef CRC32_ARM64 #undef CRC32_ARM64
#undef CRC64_ARM64_CLMUL #undef CRC64_ARM64_CLMUL
#undef CRC_USE_IFUNC
#undef CRC_USE_GENERIC_FOR_SMALL_INPUTS #undef CRC_USE_GENERIC_FOR_SMALL_INPUTS
// ARM64 CRC32 instruction is only useful for CRC32. Currently, only // ARM64 CRC32 instruction is only useful for CRC32. Currently, only
@ -109,9 +107,6 @@
# define CRC64_ARCH_OPTIMIZED 1 # define CRC64_ARCH_OPTIMIZED 1
# define CRC_X86_CLMUL 1 # define CRC_X86_CLMUL 1
# ifdef HAVE_FUNC_ATTRIBUTE_IFUNC
# define CRC_USE_IFUNC 1
# endif
/* /*
// The generic code is much faster with 1-8-byte inputs and // The generic code is much faster with 1-8-byte inputs and
// has similar performance up to 16 bytes at least in // has similar performance up to 16 bytes at least in
@ -121,9 +116,7 @@
// for bigger inputs. It saves a little in code size since // for bigger inputs. It saves a little in code size since
// the special cases for 0-16-byte inputs will be omitted // the special cases for 0-16-byte inputs will be omitted
// from the CLMUL code. // from the CLMUL code.
# ifndef CRC_USE_IFUNC # define CRC_USE_GENERIC_FOR_SMALL_INPUTS 1
# define CRC_USE_GENERIC_FOR_SMALL_INPUTS 1
# endif
*/ */
# endif # endif
#endif #endif

11
src/liblzma/check/crc_x86_clmul.h
View File

@ -385,15 +385,8 @@ crc64_arch_optimized(const uint8_t *buf, size_t size, uint64_t crc)
#endif // BUILDING_CRC64_CLMUL #endif // BUILDING_CRC64_CLMUL
// is_arch_extension_supported() must be inlined in this header file because // Inlining this function duplicates the function body in crc32_resolve() and
// the ifunc resolver function may not support calling a function in another // crc64_resolve(), but this is acceptable because this is a tiny function.
// translation unit. Depending on compiler-toolchain and flags, a call to
// a function defined in another translation unit could result in a
// reference to the PLT, which is unsafe to do in an ifunc resolver. The
// ifunc resolver runs very early when loading a shared library, so the PLT
// entries may not be setup at that time. Inlining this function duplicates
// the function body in crc32_resolve() and crc64_resolve(), but this is
// acceptable because the function results in very few instructions.
static inline bool static inline bool
is_arch_extension_supported(void) is_arch_extension_supported(void)
{ {