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authorDaniele Buono <dbuono@linux.vnet.ibm.com>2020-05-29 16:51:19 -0400
committerStefan Hajnoczi <stefanha@redhat.com>2020-06-23 15:46:05 +0100
commit58ebc2c31337734a8a79b0566b31b19040deb2ea (patch)
tree0d085b3db59d811a055a23bea18537aa60da5d14 /util/coroutine-ucontext.c
parentddd633e525fec68437d04b074130aedc9d461331 (diff)
coroutine: support SafeStack in ucontext backend
LLVM's SafeStack instrumentation does not yet support programs that make use of the APIs in ucontext.h With the current implementation of coroutine-ucontext, the resulting binary is incorrect, with different coroutines sharing the same unsafe stack and producing undefined behavior at runtime. This fix allocates an additional unsafe stack area for each coroutine, and sets the new unsafe stack pointer before calling swapcontext() in qemu_coroutine_new. This is the only place where the pointer needs to be manually updated, since sigsetjmp/siglongjmp are already instrumented by LLVM to properly support SafeStack. The additional stack is then freed in qemu_coroutine_delete. Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com> Message-id: 20200529205122.714-2-dbuono@linux.vnet.ibm.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'util/coroutine-ucontext.c')
-rw-r--r--util/coroutine-ucontext.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c
index 613f4c118e..f0b66320e1 100644
--- a/util/coroutine-ucontext.c
+++ b/util/coroutine-ucontext.c
@@ -45,6 +45,11 @@ typedef struct {
Coroutine base;
void *stack;
size_t stack_size;
+#ifdef CONFIG_SAFESTACK
+ /* Need an unsafe stack for each coroutine */
+ void *unsafe_stack;
+ size_t unsafe_stack_size;
+#endif
sigjmp_buf env;
void *tsan_co_fiber;
@@ -179,6 +184,10 @@ Coroutine *qemu_coroutine_new(void)
co = g_malloc0(sizeof(*co));
co->stack_size = COROUTINE_STACK_SIZE;
co->stack = qemu_alloc_stack(&co->stack_size);
+#ifdef CONFIG_SAFESTACK
+ co->unsafe_stack_size = COROUTINE_STACK_SIZE;
+ co->unsafe_stack = qemu_alloc_stack(&co->unsafe_stack_size);
+#endif
co->base.entry_arg = &old_env; /* stash away our jmp_buf */
uc.uc_link = &old_uc;
@@ -203,6 +212,22 @@ Coroutine *qemu_coroutine_new(void)
COROUTINE_YIELD,
&fake_stack_save,
co->stack, co->stack_size, co->tsan_co_fiber);
+
+#ifdef CONFIG_SAFESTACK
+ /*
+ * Before we swap the context, set the new unsafe stack
+ * The unsafe stack grows just like the normal stack, so start from
+ * the last usable location of the memory area.
+ * NOTE: we don't have to re-set the usp afterwards because we are
+ * coming back to this context through a siglongjmp.
+ * The compiler already wrapped the corresponding sigsetjmp call with
+ * code that saves the usp on the (safe) stack before the call, and
+ * restores it right after (which is where we return with siglongjmp).
+ */
+ void *usp = co->unsafe_stack + co->unsafe_stack_size;
+ __safestack_unsafe_stack_ptr = usp;
+#endif
+
swapcontext(&old_uc, &uc);
}
@@ -235,6 +260,9 @@ void qemu_coroutine_delete(Coroutine *co_)
#endif
qemu_free_stack(co->stack, co->stack_size);
+#ifdef CONFIG_SAFESTACK
+ qemu_free_stack(co->unsafe_stack, co->unsafe_stack_size);
+#endif
g_free(co);
}