mirror of https://git.tukaani.org/xz.git
liblzma: Disable external SHA-256 by default.
This is the sane thing to do. The conflict with OpenSSL on some OSes and especially that the OS-provided versions can be significantly slower makes it clear that it was a mistake to have the external SHA-256 support enabled by default. Those who want it can now pass --enable-external-sha256 to configure. INSTALL was updated with notes about OSes where this can be a bad idea. The SHA-256 detection code in configure.ac had some bugs that could lead to a build failure in some situations. These were fixed, although it doesn't matter that much now that the external SHA-256 is disabled by default. MINIX >= 3.2.0 uses NetBSD's libc and thus has SHA256_Init in libc instead of libutil. Support for the libutil version was removed.
This commit is contained in:
Lasse Collin
parent
6fd5ecb589
commit
ac398c3baf
36
INSTALL
36
INSTALL
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@ -246,6 +246,42 @@ XZ Utils Installation
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the liblzma ABI, so this option should be used only when
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it is known to not cause problems.
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--enable-external-sha256
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Try to use SHA-256 code from the operating system libc
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or similar base system libraries. This doesn't try to
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use OpenSSL or libgcrypt or such libraries.
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The reasons to use this option:
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- It makes liblzma slightly smaller.
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- It might improve SHA-256 speed if the implementation
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in the operating is very good (but see below).
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External SHA-256 is disabled by default for two reasons:
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- On some operating systems the symbol names of the
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SHA-256 functions conflict with OpenSSL's libcrypto.
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This causes weird problems such as decompression
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errors if an application is linked against both
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liblzma and libcrypto. This problem affects at least
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FreeBSD 10 and older and MINIX 3.3.0 and older, but
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other OSes that provide a function "SHA256_Init" might
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also be affected. FreeBSD 11 has the problem fixed.
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NetBSD had the problem but it was fixed it in 2009
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already. OpenBSD uses "SHA256Init" and thus never had
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a conflict with libcrypto.
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- The SHA-256 code in liblzma is faster than the SHA-256
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code provided by some operating systems. If you are
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curious, build two copies of xz (internal and external
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SHA-256) and compare the decompression (xz --test)
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times:
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dd if=/dev/zero bs=1024k count=1024 \
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| xz -v -0 -Csha256 > foo.xz
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time xz --test foo.xz
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--disable-xz
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--disable-xzdec
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--disable-lzmadec
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72
configure.ac
72
configure.ac
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@ -275,6 +275,20 @@ m4_foreach([NAME], [SUPPORTED_CHECKS],
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[AM_CONDITIONAL(COND_CHECK_[]m4_toupper(NAME), test "x$enable_check_[]NAME" = xyes)
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])dnl
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AC_MSG_CHECKING([if external SHA-256 should be used])
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AC_ARG_ENABLE([external-sha256], AS_HELP_STRING([--enable-external-sha256],
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[Use SHA-256 code from the operating system.
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See INSTALL for possible subtle problems.]),
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[], [enable_external_sha256=no])
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if test "x$enable_check_sha256" != "xyes"; then
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enable_external_sha256=no
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fi
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if test "x$enable_external_sha256" = xyes; then
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AC_MSG_RESULT([yes])
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else
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AC_MSG_RESULT([no])
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fi
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###########################
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# Assembler optimizations #
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@ -669,48 +683,34 @@ TUKLIB_PHYSMEM
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TUKLIB_CPUCORES
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TUKLIB_MBSTR
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# Check for system-provided SHA-256. The supported implementations are listed
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# below. The detection for the ones marked with [*] has been intentionally
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# disabled because they have symbol name conflicts with OpenSSL's libcrypto
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# which can cause weird problems (clean namespaces would make things too
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# boring, I guess).
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# If requsted, check for system-provided SHA-256. At least the following
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# implementations are supported:
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#
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# OS Headers Library Type Function
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# FreeBSD sys/types.h + sha256.h libmd SHA256_CTX SHA256_Init [*]
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# FreeBSD sys/types.h + sha256.h libmd SHA256_CTX SHA256_Init
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# NetBSD sys/types.h + sha2.h SHA256_CTX SHA256_Init
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# OpenBSD sys/types.h + sha2.h SHA2_CTX SHA256Init
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# Solaris sys/types.h + sha2.h libmd SHA256_CTX SHA256Init
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# MINIX 3 sys/types.h + minix/sha2.h libutil SHA256_CTX SHA256_Init [*]
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# MINIX 3 sys/types.h + sha2.h SHA256_CTX SHA256_Init
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# Darwin CommonCrypto/CommonDigest.h CC_SHA256_CTX CC_SHA256_Init
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#
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# Notes:
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#
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# - NetBSD's SHA256_Init doesn't conflict with libcrypto because
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# libcrypto on NetBSD was made to use the libc implementation to avoid
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# this exact symbol conflict problem:
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# http://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2009-012.txt.asc
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#
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# - As of 2016-03-10, FreeBSD seems to have the issue fixed in SVN head
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# but not in the FreeBSD 10 branch.
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#
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# - Darwin's CC_SHA256_Update takes buffer size as uint32_t instead
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# Note that Darwin's CC_SHA256_Update takes buffer size as uint32_t instead
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# of size_t.
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#
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# We don't check for e.g. OpenSSL or libgcrypt because we don't want
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# to introduce dependencies to other packages by default. Maybe such
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# libraries could be supported via additional configure options though.
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#
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if test "x$enable_check_sha256" = "xyes"; then
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sha256_header_found=no
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sha256_type_found=no
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sha256_func_found=no
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if test "x$enable_external_sha256" = "xyes"; then
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# Test for Common Crypto before others, because Darwin has sha256.h
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# too and we don't want to use that, because on older versions it
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# uses OpenSSL functions, whose SHA256_Init is not guaranteed to
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# succeed.
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sha256_header_found=no
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AC_CHECK_HEADERS(
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[CommonCrypto/CommonDigest.h sha256.h sha2.h minix/sha2.h],
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[CommonCrypto/CommonDigest.h sha256.h sha2.h],
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[sha256_header_found=yes ; break])
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if test "x$sha256_header_found" = xyes; then
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AC_CHECK_TYPES([CC_SHA256_CTX, SHA256_CTX, SHA2_CTX], [], [],
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AC_CHECK_TYPES([CC_SHA256_CTX, SHA256_CTX, SHA2_CTX],
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[sha256_type_found=yes], [],
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[[#ifdef HAVE_SYS_TYPES_H
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# include <sys/types.h>
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#endif
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@ -722,21 +722,19 @@ if test "x$enable_check_sha256" = "xyes"; then
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#endif
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#ifdef HAVE_SHA2_H
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# include <sha2.h>
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#endif
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#ifdef HAVE_MINIX_SHA2_H
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# include <minix/sha2.h>
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#endif]])
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dnl Omit detection of the FreeBSD and MINIX 3 versions:
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dnl AC_SEARCH_LIBS([SHA256_Init], [md util])
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if test "x$sha256_type_found" = xyes ; then
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AC_SEARCH_LIBS([SHA256Init], [md])
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AC_CHECK_FUNCS([CC_SHA256_Init SHA256_Init SHA256Init],
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[break])
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AC_SEARCH_LIBS([SHA256_Init], [md])
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AC_CHECK_FUNCS([CC_SHA256_Init SHA256Init SHA256_Init],
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[sha256_func_found=yes ; break])
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fi
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fi
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fi
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AM_CONDITIONAL([COND_INTERNAL_SHA256],
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[test "x$ac_cv_func_SHA256_Init" != xyes \
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&& test "x$ac_cv_func_SHA256Init" != xyes \
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&& test "x$ac_cv_func_CC_SHA256_Init" != xyes])
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AM_CONDITIONAL([COND_INTERNAL_SHA256], [test "x$sha256_func_found" = xno])
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if test "x$enable_external_sha256$sha256_func_found" = xyesno; then
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AC_MSG_ERROR([--enable-external-sha256 was specified but no supported external SHA-256 implementation was found])
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fi
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# Check for SSE2 intrinsics.
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AC_CHECK_DECL([_mm_movemask_epi8],
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@ -15,11 +15,10 @@
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#include "common.h"
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// If either the data type or the function for external SHA-256 is missing,
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// use the internal SHA-256 code.
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#if !(defined(HAVE_CC_SHA256_CTX) || defined(HAVE_SHA256_CTX) \
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|| defined(HAVE_SHA2_CTX)) \
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|| !(defined(HAVE_CC_SHA256_INIT) \
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// If the function for external SHA-256 is missing, use the internal SHA-256
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// code. Due to how configure works, these defines can only get defined when
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// both a usable header and a type have already been found.
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#if !(defined(HAVE_CC_SHA256_INIT) \
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|| defined(HAVE_SHA256_INIT) \
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|| defined(HAVE_SHA256INIT))
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# define HAVE_INTERNAL_SHA256 1
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@ -35,9 +34,6 @@
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#elif defined(HAVE_SHA2_H)
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# include <sys/types.h>
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# include <sha2.h>
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#elif defined(HAVE_MINIX_SHA2_H)
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# include <sys/types.h>
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# include <minix/sha2.h>
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#endif
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#if defined(HAVE_INTERNAL_SHA256)
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