115 lines
4.8 KiB
Diff
115 lines
4.8 KiB
Diff
From 2c6bf28619c9b3bf713f7f5319c5d750a6c297ae Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?S=C3=B6ren=20Tempel?= <soeren@soeren-tempel.net>
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Date: Fri, 21 Jan 2022 19:22:46 +0000
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Subject: [PATCH] Disable -fsplit-stack support on non-glibc targets
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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The -fsplit-stack option requires the pthread_t TCB definition in the
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libc to provide certain struct fields at specific hardcoded offsets. As
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far as I know, only glibc provides these fields at the required offsets.
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Most notably, musl libc does not have these fields. However, since gcc
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accesses the fields using a fixed offset, this does not cause a
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compile-time error, but instead results in a silent memory corruption at
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run-time with musl libc. For example, on s390x libgcc's
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__stack_split_initialize CTOR will overwrite the cancel field in the
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pthread_t TCB on musl.
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The -fsplit-stack option is used within the gcc code base itself by
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gcc-go (if available). On musl-based systems with split-stack support
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(i.e. s390x or x86) this causes Go programs compiled with gcc-go to
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misbehave at run-time.
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This patch fixes gcc-go on musl by disabling -fsplit-stack in gcc itself
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since it is not supported on non-glibc targets anyhow. This is achieved
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by checking if gcc targets a glibc-based system. This check has been
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added for x86 and s390x, the rs6000 config already checks for
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TARGET_GLIBC_MAJOR. Other architectures do not have split-stack
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support. With this patch applied, the gcc-go configure script will
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detect that -fsplit-stack support is not available and will not use it.
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See https://www.openwall.com/lists/musl/2012/10/16/12
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This patch was written under the assumption that glibc is the only libc
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implementation which supports the required fields at the required
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offsets in the pthread_t TCB. The patch has been tested on Alpine Linux
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Edge on the s390x and x86 architectures by bootstrapping Google's Go
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implementation with gcc-go.
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Signed-off-by: Sören Tempel <soeren@soeren-tempel.net>
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gcc/ChangeLog:
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* common/config/s390/s390-common.c (s390_supports_split_stack):
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Only support split-stack on glibc targets.
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* config/i386/gnu-user-common.h (STACK_CHECK_STATIC_BUILTIN): Ditto.
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* config/i386/gnu.h (defined): Ditto.
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---
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gcc/common/config/s390/s390-common.c | 14 ++++++++++----
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gcc/config/i386/gnu-user-common.h | 5 +++--
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gcc/config/i386/gnu.h | 5 ++++-
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3 files changed, 17 insertions(+), 7 deletions(-)
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diff --git a/gcc/common/config/s390/s390-common.c b/gcc/common/config/s390/s390-common.c
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index b6bc8501742..8c1e590322d 100644
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--- a/gcc/common/config/s390/s390-common.c
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+++ b/gcc/common/config/s390/s390-common.c
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@@ -116,13 +116,19 @@ s390_handle_option (struct gcc_options *opts ATTRIBUTE_UNUSED,
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/* -fsplit-stack uses a field in the TCB, available with glibc-2.23.
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We don't verify it, since earlier versions just have padding at
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- its place, which works just as well. */
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+ its place, which works just as well. For other libc implementations
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+ we disable the feature entirely to avoid corrupting the TCB. */
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static bool
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-s390_supports_split_stack (bool report ATTRIBUTE_UNUSED,
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- struct gcc_options *opts ATTRIBUTE_UNUSED)
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+s390_supports_split_stack (bool report,
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+ struct gcc_options *opts)
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{
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- return true;
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+ if (opts->x_linux_libc == LIBC_GLIBC)
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+ return true;
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+
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+ if (report)
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+ error ("%<-fsplit-stack%> currently only supported on GNU/Linux");
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+ return false;
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}
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#undef TARGET_DEFAULT_TARGET_FLAGS
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diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
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index 00226f5a455..6e13315b5a3 100644
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--- a/gcc/config/i386/gnu-user-common.h
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+++ b/gcc/config/i386/gnu-user-common.h
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@@ -66,7 +66,8 @@ along with GCC; see the file COPYING3. If not see
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#define STACK_CHECK_STATIC_BUILTIN 1
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/* We only build the -fsplit-stack support in libgcc if the
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- assembler has full support for the CFI directives. */
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-#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE
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+ assembler has full support for the CFI directives and
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+ targets glibc. */
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+#if HAVE_GAS_CFI_PERSONALITY_DIRECTIVE && OPTION_GLIBC
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#define TARGET_CAN_SPLIT_STACK
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#endif
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diff --git a/gcc/config/i386/gnu.h b/gcc/config/i386/gnu.h
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index 25fbc07f58c..afd3e8e8841 100644
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--- a/gcc/config/i386/gnu.h
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+++ b/gcc/config/i386/gnu.h
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@@ -35,7 +35,10 @@ along with GCC. If not, see <http://www.gnu.org/licenses/>.
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crti.o%s %{static:crtbeginT.o%s;shared|pie:crtbeginS.o%s;:crtbegin.o%s}"
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#endif
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-#ifdef TARGET_LIBC_PROVIDES_SSP
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+/* -fsplit-stack uses a field in the TCB at a fixed offset. This
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+ field is only available for glibc. Disable -fsplit-stack for
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+ other libc implementations to avoid silent TCB corruptions. */
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+#if defined (TARGET_LIBC_PROVIDES_SSP) && OPTION_GLIBC
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/* i386 glibc provides __stack_chk_guard in %gs:0x14. */
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#define TARGET_THREAD_SSP_OFFSET 0x14
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--
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2.35.1
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