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aarch64: configure check for pac-ret code generation 

Return address signing requires unwinder support, which is
present in libgcc since >=gcc-7, however due to bugs the
support may be broken in <gcc-10 (and similarly there may
be issues in custom unwinders), so pac-ret is not always
safe to use. So in assembly code glibc should only use
pac-ret if the compiler uses it too. Unfortunately there
is no predefined feature macro for it set by the compiler
so pac-ret is inferred from the code generation.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
This commit is contained in:
Szabolcs Nagy 2020-05-07 18:30:12 +01:00
parent de9301c02e
commit 9e1751e6d6
3 changed files with 63 additions and 0 deletions
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3
config.h.in
View File

@ -112,6 +112,9 @@
/* AArch64 BTI support enabled. */ /* AArch64 BTI support enabled. */
#define HAVE_AARCH64_BTI 0 #define HAVE_AARCH64_BTI 0
/* AArch64 PAC-RET code generation is enabled. */
#define HAVE_AARCH64_PAC_RET 0
/* C-SKY ABI version. */ /* C-SKY ABI version. */
#undef CSKYABI #undef CSKYABI

39
sysdeps/aarch64/configure vendored
View File

@ -216,3 +216,42 @@ if test $libc_cv_aarch64_bti = yes; then
$as_echo "#define HAVE_AARCH64_BTI 1" >>confdefs.h $as_echo "#define HAVE_AARCH64_BTI 1" >>confdefs.h
fi fi
# Check if glibc is built with return address signing, i.e.
# if -mbranch-protection=pac-ret is on. We need this because
# pac-ret relies on unwinder support so it's not safe to use
# it in assembly code unconditionally, but there is no
# feature test macro for it in gcc.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if pac-ret is enabled" >&5
$as_echo_n "checking if pac-ret is enabled... " >&6; }
if ${libc_cv_aarch64_pac_ret+:} false; then :
$as_echo_n "(cached) " >&6
else
cat > conftest.c <<EOF
int bar (void);
int foo (void) { return bar () + 1; }
EOF
libc_cv_aarch64_pac_ret=no
if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -S -o conftest.s conftest.c'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; } \
&& { ac_try='grep -q -E '\''(hint( | )+25|paciasp)'\'' conftest.s'
{ { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
(eval $ac_try) 2>&5
ac_status=$?
$as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
test $ac_status = 0; }; }
then
libc_cv_aarch64_pac_ret=yes
fi
rm -rf conftest.*
fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_aarch64_pac_ret" >&5
$as_echo "$libc_cv_aarch64_pac_ret" >&6; }
if test $libc_cv_aarch64_pac_ret = yes; then
$as_echo "#define HAVE_AARCH64_PAC_RET 1" >>confdefs.h
fi

21
sysdeps/aarch64/configure.ac
View File

@ -40,3 +40,24 @@ LIBC_CONFIG_VAR([aarch64-bti], [$libc_cv_aarch64_bti])
if test $libc_cv_aarch64_bti = yes; then if test $libc_cv_aarch64_bti = yes; then
AC_DEFINE(HAVE_AARCH64_BTI) AC_DEFINE(HAVE_AARCH64_BTI)
fi fi
# Check if glibc is built with return address signing, i.e.
# if -mbranch-protection=pac-ret is on. We need this because
# pac-ret relies on unwinder support so it's not safe to use
# it in assembly code unconditionally, but there is no
# feature test macro for it in gcc.
AC_CACHE_CHECK([if pac-ret is enabled], [libc_cv_aarch64_pac_ret], [dnl
cat > conftest.c <<EOF
int bar (void);
int foo (void) { return bar () + 1; }
EOF
libc_cv_aarch64_pac_ret=no
if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS -S -o conftest.s conftest.c]) \
&& AC_TRY_COMMAND([grep -q -E '\''(hint( | )+25|paciasp)'\'' conftest.s])
then
libc_cv_aarch64_pac_ret=yes
fi
rm -rf conftest.*])
if test $libc_cv_aarch64_pac_ret = yes; then
AC_DEFINE(HAVE_AARCH64_PAC_RET)
fi