From: Greg Hackmann Date: Tue, 4 Dec 2018 10:23:53 -0800 Subject: [LTP] [PATCH] cve/stack_clash: inhibit test-breaking optimizations Message-ID: <20181204182353.86453-1-ghackmann@google.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ltp@lists.linux.it stack_clash relies on the compiler doing fairly specific things with the stack pointer. We've run into a couple of places where clang optimized away the intended behavior: (1) exhaust_stack_into_sigsegv() tries to grow the stack via infinite recursion. Since this happens through a tail call, the compiler may transform this into an iterative equivalent which loops forever without growing the stack. -fno-optimize-sibling-calls explicitly blocks this optimization on both gcc and clang. (2) If preallocate_stack() is inlined, its ~1 MB stack frame may not be released until the parent function returns. This can cause the stack pointer to cross the stack guard in the middle of do_child(), before the SIGSEGV handler has actually been set up. Prevent this by marking the function noinline. Signed-off-by: Greg Hackmann --- testcases/cve/Makefile | 2 ++ testcases/cve/stack_clash.c | 2 +- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/testcases/cve/Makefile b/testcases/cve/Makefile index 3a05dd4fe..6dc401cff 100644 --- a/testcases/cve/Makefile +++ b/testcases/cve/Makefile @@ -19,6 +19,8 @@ include $(top_srcdir)/include/mk/testcases.mk CFLAGS += -D_GNU_SOURCE +stack_clash: CFLAGS += -fno-optimize-sibling-calls + cve-2016-7042: LDLIBS += $(KEYUTILS_LIBS) cve-2016-7117: CFLAGS += -pthread diff --git a/testcases/cve/stack_clash.c b/testcases/cve/stack_clash.c index f25e19b3f..ac4a31af6 100644 --- a/testcases/cve/stack_clash.c +++ b/testcases/cve/stack_clash.c @@ -136,7 +136,7 @@ void dump_proc_self_maps(void) tst_run_cmd(cmd, NULL, NULL, 0); } -void preallocate_stack(unsigned long required) +void __attribute__((noinline)) preallocate_stack(unsigned long required) { volatile char *garbage; -- 2.20.0.rc1.387.gf8505762e3-goog