Extract hardening CFLAGS to a special $hardenflags variable

This changes the automatic detection of -fstack-protector,
-D_FORTIFY_SOURCE, and -mbranch-protection to write to $hardenflags
instead of $XCFLAGS. The definition of $cflags is changed to
"$hardenflags $orig_cflags $optflags $debugflags $warnflags" to match.

Furthermore, these flags are _prepended_ to $hardenflags, rather than
appended.

The implications of doing this are as follows:

* If a CRuby builder specifies cflags="-mbranch-protection=foobar" at
  the ./configure script, and the configure script detects that
  -mbranch-protection=pac-ret is accepted, then GCC will be invoked as
  "gcc -mbranch-protection=pac-ret -mbranch-protection=foobar". Since
  the last flags take precedence, that means that user-supplied values
  of these flags in $cflags will take priority.
* Likewise, if a CRuby builder explicitly specifies
  "hardenflags=-mbranch-protection=foobar", because we _prepend_ to
  $hardenflags in our autoconf script, we will still invoke GCC as
  "gcc -mbranch-protection=pac-ret -mbranch-protection=foobar".
* If a CRuby builder specifies CFLAGS="..." at the configure line,
  automatic detection of hardening flags is ignored as before.
* C extensions will _also_ be built with hardening flags now as well
  (this was not the case by default before because the detected flags
  went into $XCFLAGS).

Additionally, as part of this work, I changed how the detection of
PAC/BTI in Context.S works. Rather than appending the autodetected
option to ASFLAGS, we simply compile a set of test programs with the
actual CFLAGS in use to determine what PAC/BTI settings were actually
chosen by the builder. Context.S is made aware of these choices through
some custom macros.

The result of this work is that:

* Ruby will continue to choose some sensible defaults for hardening
  options for the C compiler
* Distributors are able to specify CFLAGS that are consistent with their
  distribution and override these defaults
* Context.S will react to whatever -mbranch-protection is actually in
  use, not what was autodetected
* Extensions get built with hardening flags too.

[Bug #20154]
[Bug #20520]
This commit is contained in:
KJ Tsanaktsidis 2024-06-09 21:15:39 +10:00
parent 6086bae5c8
commit 0ccb80d6bf
5 changed files with 100 additions and 17 deletions

View File

@ -360,7 +360,7 @@ test -z "$warnflags" ||
AS_IF([test -z "${CFLAGS+set}"], [
cflags=`echo " $cflags " | sed "$cflagspat;s/^ *//;s/ *$//"`
orig_cflags="$cflags"
cflags="$cflags "'${optflags} ${debugflags} ${warnflags}'
cflags='${hardenflags} '"$cflags "'${optflags} ${debugflags} ${warnflags}'
])
dnl AS_IF([test -z "${CXXFLAGS+set}"], [
dnl cxxflags=`echo " $cxxflags " | sed "$cflagspat;s/^ *//;s/ *$//"`
@ -813,7 +813,7 @@ AS_IF([test "$GCC" = yes], [
[fortify_source=$enableval])
AS_IF([test "x$fortify_source" != xno], [
RUBY_TRY_CFLAGS([$optflags -D_FORTIFY_SOURCE=2],
[RUBY_APPEND_OPTION(XCFLAGS, -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2)], [],
[RUBY_PREPEND_OPTION(hardenflags, -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2)], [],
[@%:@include <stdio.h>])
])
@ -834,20 +834,24 @@ AS_IF([test "$GCC" = yes], [
AC_MSG_CHECKING([for -fstack-protector])
AC_MSG_RESULT(["$stack_protector"])
AS_CASE(["$stack_protector"], [-*], [
RUBY_APPEND_OPTION(XCFLAGS, $stack_protector)
RUBY_APPEND_OPTION(XLDFLAGS, $stack_protector)
RUBY_APPEND_OPTION(LDFLAGS, $stack_protector)
RUBY_PREPEND_OPTION(hardenflags, $stack_protector)
RUBY_APPEND_OPTION(XLDFLAGS, $stack_protector)
RUBY_APPEND_OPTION(LDFLAGS, $stack_protector)
])
# aarch64 branch protection
AS_CASE(["$target_cpu"], [aarch64], [
AS_FOR(option, opt, [-mbranch-protection=pac-ret -msign-return-address=all], [
RUBY_TRY_CFLAGS(option, [branch_protection=yes], [branch_protection=no])
# Try these flags in the _prepended_ position - i.e. we want to try building a program
# with CFLAGS="-mbranch-protection=pac-ret $CFLAGS". If the builder has provided different
# branch protection flags in CFLAGS, we don't want to overwrite those. We just want to
# find some branch protection flags which work if none were provided.
RUBY_TRY_CFLAGS_PREPEND(option, [branch_protection=yes], [branch_protection=no])
AS_IF([test "x$branch_protection" = xyes], [
# C compiler and assembler must be consistent for -mbranch-protection
# since they both check `__ARM_FEATURE_PAC_DEFAULT` definition.
RUBY_APPEND_OPTION(XCFLAGS, option)
RUBY_APPEND_OPTION(ASFLAGS, option)
# _prepend_ the options to CFLAGS, so that user-provided flags will overwrite them.
# These CFLAGS are used during the configure script to compile further test programs;
# however, $harden_flags is prepended separately to CFLAGS at the end of the script.
RUBY_PREPEND_OPTION(hardenflags, $opt)
break
])
])
@ -995,6 +999,59 @@ AC_SUBST(incflags, "$INCFLAGS")
test -z "${ac_env_CFLAGS_set}" -a -n "${cflags+set}" && eval CFLAGS="\"$cflags $ARCH_FLAG\""
test -z "${ac_env_CXXFLAGS_set}" -a -n "${cxxflags+set}" && eval CXXFLAGS="\"$cxxflags $ARCH_FLAG\""
# The lines above expand out the $cflags/$optflags/$debugflags/$hardenflags variables into the
# CFLAGS variable. So, at this point, we have a $CFLAGS var with the actual compiler flags we're
# going to use.
# That means this is the right time to check what branch protection flags are going to be in use
# and define appropriate macros for use in Context.S based on this
AS_CASE(["$target_cpu"], [aarch64], [
AC_CACHE_CHECK([whether __ARM_FEATURE_BTI_DEFAULT is defined],
rb_cv_aarch64_bti_enabled,
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[
@%:@ifndef __ARM_FEATURE_BTI_DEFAULT
@%:@error "__ARM_FEATURE_BTI_DEFAULT not defined"
@%:@endif
]])],
[rb_cv_aarch64_bti_enabled=yes],
[rb_cv_aarch64_bti_enabled=no])
)
AS_IF([test "$rb_cv_aarch64_bti_enabled" = yes],
AC_DEFINE(RUBY_AARCH64_BTI_ENABLED, 1))
AC_CACHE_CHECK([whether __ARM_FEATURE_PAC_DEFAULT is defined],
rb_cv_aarch64_pac_enabled,
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[
@%:@ifndef __ARM_FEATURE_PAC_DEFAULT
@%:@error "__ARM_FEATURE_PAC_DEFAULT not defined"
@%:@endif
]])],
[rb_cv_aarch64_pac_enabled=yes],
[rb_cv_aarch64_pac_enabled=no])
)
AS_IF([test "$rb_cv_aarch64_pac_enabled" = yes],
AC_DEFINE(RUBY_AARCH64_PAC_ENABLED, 1))
# Context.S will only ever sign its return address with the A-key; it doesn't support
# the B-key at the moment.
AS_IF([test "$rb_cv_aarch64_pac_enabled" = yes], [
AC_CACHE_CHECK([whether __ARM_FEATURE_PAC_DEFAULT specifies the b-key bit 0x02],
rb_cv_aarch64_pac_b_key,
AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[
@%:@ifdef __ARM_FEATURE_PAC_DEFAULT
@%:@if __ARM_FEATURE_PAC_DEFAULT & 0x02
@%:@error "__ARM_FEATURE_PAC_DEFAULT specifies B key"
@%:@endif
@%:@endif
]])],
[rb_cv_aarch64_pac_b_key=no],
[rb_cv_aarch64_pac_b_key=yes])
)
AS_IF([test "$rb_cv_aarch64_pac_b_key" = yes],
AC_MSG_ERROR(-mbranch-protection flag specified b-key but Ruby's Context.S does not support this yet.))
])
])
AC_CACHE_CHECK([whether compiler has statement and declarations in expressions],
rb_cv_have_stmt_and_decl_in_expr,
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],[[ __extension__ ({ int a = 0; a; }); ]])],
@ -4226,12 +4283,13 @@ AS_IF([test "${ARCH_FLAG}"], [
rb_cv_warnflags=`echo "$rb_cv_warnflags" | sed 's/^ *//;s/ *$//'`
warnflags="$rb_cv_warnflags"
AC_SUBST(cppflags)dnl
AC_SUBST(cflags, ["${orig_cflags:+$orig_cflags }"'${optflags} ${debugflags} ${warnflags}'])dnl
AC_SUBST(cflags, ['${hardenflags} '"${orig_cflags:+$orig_cflags }"' ${optflags} ${debugflags} ${warnflags}'])dnl
AC_SUBST(cxxflags)dnl
AC_SUBST(optflags)dnl
AC_SUBST(debugflags)dnl
AC_SUBST(warnflags)dnl
AC_SUBST(strict_warnflags)dnl
AC_SUBST(hardenflags)dnl
AC_SUBST(XCFLAGS)dnl
AC_SUBST(XLDFLAGS)dnl
AC_SUBST(EXTLDFLAGS)dnl
@ -4691,6 +4749,7 @@ config_summary "DLDFLAGS" "$DLDFLAGS"
config_summary "optflags" "$optflags"
config_summary "debugflags" "$debugflags"
config_summary "warnflags" "$warnflags"
config_summary "hardenflags" "$hardenflags"
config_summary "strip command" "$STRIP"
config_summary "install doc" "$DOCTARGETS"
config_summary "YJIT support" "$YJIT_SUPPORT"

View File

@ -5,6 +5,8 @@
## Copyright, 2018, by Samuel Williams.
##
#include "ruby/config.h"
#define TOKEN_PASTE(x,y) x##y
#define PREFIXED_SYMBOL(prefix,name) TOKEN_PASTE(prefix,name)
@ -27,10 +29,10 @@
.global PREFIXED_SYMBOL(SYMBOL_PREFIX,coroutine_transfer)
PREFIXED_SYMBOL(SYMBOL_PREFIX,coroutine_transfer):
#if defined(__ARM_FEATURE_PAC_DEFAULT) && (__ARM_FEATURE_PAC_DEFAULT != 0)
#if defined(RUBY_AARCH64_PAC_ENABLED)
# paciasp (it also acts as BTI landing pad, so no need to insert BTI also)
hint #25
#elif defined(__ARM_FEATURE_BTI_DEFAULT) && (__ARM_FEATURE_BTI_DEFAULT != 0)
#elif defined(RUBY_AARCH64_BTI_ENABLED)
# For the case PAC is not enabled but BTI is.
# bti c
hint #34
@ -73,7 +75,7 @@ PREFIXED_SYMBOL(SYMBOL_PREFIX,coroutine_transfer):
# Pop stack frame
add sp, sp, 0xa0
#if defined(__ARM_FEATURE_PAC_DEFAULT) && (__ARM_FEATURE_PAC_DEFAULT != 0)
#if defined(RUBY_AARCH64_PAC_ENABLED)
# autiasp: Authenticate x30 (LR) with SP and key A
hint #29
#endif
@ -85,18 +87,18 @@ PREFIXED_SYMBOL(SYMBOL_PREFIX,coroutine_transfer):
.section .note.GNU-stack,"",%progbits
#endif
#if __ARM_FEATURE_BTI_DEFAULT != 0 || __ARM_FEATURE_PAC_DEFAULT != 0
#if defined(RUBY_AARCH64_BTI_ENABLED) || defined(RUBY_AARCH64_PAC_ENABLED)
/* See "ELF for the Arm 64-bit Architecture (AArch64)"
https://github.com/ARM-software/abi-aa/blob/2023Q3/aaelf64/aaelf64.rst#program-property */
# define GNU_PROPERTY_AARCH64_FEATURE_1_BTI (1<<0)
# define GNU_PROPERTY_AARCH64_FEATURE_1_PAC (1<<1)
# if __ARM_FEATURE_BTI_DEFAULT != 0
# if defined(RUBY_AARCH64_BTI_ENABLED)
# define BTI_FLAG GNU_PROPERTY_AARCH64_FEATURE_1_BTI
# else
# define BTI_FLAG 0
# endif
# if __ARM_FEATURE_PAC_DEFAULT != 0
# if defined(RUBY_AARCH64_PAC_ENABLED)
# define PAC_FLAG GNU_PROPERTY_AARCH64_FEATURE_1_PAC
# else
# define PAC_FLAG 0

View File

@ -89,6 +89,7 @@ cflags = @cflags@
optflags = @optflags@
debugflags = @debugflags@
warnflags = @warnflags@ @strict_warnflags@
hardenflags = @hardenflags@
cppflags = @cppflags@
incflags = @incflags@
RUBY_DEVEL = @RUBY_DEVEL@ # "yes" or empty

View File

@ -3,3 +3,7 @@ AC_DEFUN([RUBY_APPEND_OPTION],
[# RUBY_APPEND_OPTION($1)
AS_CASE([" [$]{$1-} "],
[*" $2 "*], [], [' '], [ $1="$2"], [ $1="[$]$1 $2"])])dnl
AC_DEFUN([RUBY_PREPEND_OPTION],
[# RUBY_APPEND_OPTION($1)
AS_CASE([" [$]{$1-} "],
[*" $2 "*], [], [' '], [ $1="$2"], [ $1="$2 [$]$1"])])dnl

View File

@ -22,3 +22,20 @@ AC_DEFUN([RUBY_TRY_CFLAGS], [
AC_MSG_RESULT(no)],
[$4], [$5])
])dnl
AC_DEFUN([_RUBY_TRY_CFLAGS_PREPEND], [
RUBY_WERROR_FLAG([
CFLAGS="$1 [$]CFLAGS"
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[$4]], [[$5]])],
[$2], [$3])
])dnl
])dnl
AC_DEFUN([RUBY_TRY_CFLAGS_PREPEND], [
AC_MSG_CHECKING([whether ]$1[ is accepted as CFLAGS])dnl
_RUBY_TRY_CFLAGS_PREPEND([$1],
[$2
AC_MSG_RESULT(yes)],
[$3
AC_MSG_RESULT(no)],
[$4], [$5])
])dnl