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From: Szabolcs Nagy <nsz@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/nsz/pacbti-v7] aarch64: configure check for pac-ret code generation Date: Wed, 8 Jul 2020 12:09:23 +0000 (GMT) [thread overview] Message-ID: <20200708120923.3D18D38618AF@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=edd17bfbbbb6a7bfbd4150f71153f4c477a2fcf5 commit edd17bfbbbb6a7bfbd4150f71153f4c477a2fcf5 Author: Szabolcs Nagy <szabolcs.nagy@arm.com> Date: Thu May 7 18:30:12 2020 +0100 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> Diff: --- config.h.in | 3 +++ sysdeps/aarch64/configure | 39 +++++++++++++++++++++++++++++++++++++++ sysdeps/aarch64/configure.ac | 21 +++++++++++++++++++++ 3 files changed, 63 insertions(+) diff --git a/config.h.in b/config.h.in index 67169e5d01..7921917ad2 100644 --- a/config.h.in +++ b/config.h.in @@ -112,6 +112,9 @@ /* AArch64 BTI support enabled. */ #define HAVE_AARCH64_BTI 0 +/* AArch64 PAC-RET code generation is enabled. */ +#define HAVE_AARCH64_PAC_RET 0 + /* C-SKY ABI version. */ #undef CSKYABI diff --git a/sysdeps/aarch64/configure b/sysdeps/aarch64/configure index c637540436..ac3cf6fd36 100644 --- a/sysdeps/aarch64/configure +++ b/sysdeps/aarch64/configure @@ -216,3 +216,42 @@ if test $libc_cv_aarch64_bti = yes; then $as_echo "#define HAVE_AARCH64_BTI 1" >>confdefs.h 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 + $as_echo "#define HAVE_AARCH64_PAC_RET 1" >>confdefs.h + +fi diff --git a/sysdeps/aarch64/configure.ac b/sysdeps/aarch64/configure.ac index 2c2817514d..8b042d6d05 100644 --- a/sysdeps/aarch64/configure.ac +++ b/sysdeps/aarch64/configure.ac @@ -40,3 +40,24 @@ LIBC_CONFIG_VAR([aarch64-bti], [$libc_cv_aarch64_bti]) if test $libc_cv_aarch64_bti = yes; then AC_DEFINE(HAVE_AARCH64_BTI) fi + +# Check if glibc is built with return address signing, i.e. +# if -mbranch-protection=pac-ret is on. We need this because +# pac-ret relies on unwinder support so it's not safe to use +# it in assembly code unconditionally, but there is no +# feature test macro for it in gcc. +AC_CACHE_CHECK([if pac-ret is enabled], [libc_cv_aarch64_pac_ret], [dnl + cat > conftest.c <<EOF +int bar (void); +int foo (void) { return bar () + 1; } +EOF + libc_cv_aarch64_pac_ret=no + if AC_TRY_COMMAND([${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
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