[PATCH v4 03/71] tcg: Manage splitwx in tc_ptr_to_region_tree by hand

[Richard Henderson]

The use in tcg_tb_lookup is given a random pc that comes from the pc
of a signal handler.  Do not assert that the pointer is already within
the code gen buffer at all, much less the writable mirror of it.

Fixes: db0c51a3803
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---

For TCI, this indicates a bug in handle_cpu_signal, in that we
are taking PC from the host signal frame.  Which is, nearly,
unrelated to TCI at all.

The TCI "pc" is tci_tb_ptr (fixed in the next patch to at least
be thread-local).  We update this only on calls, since we don't
expect SEGV during the interpretation loop.  Which works ok for
softmmu, in which we pass down pc by hand to the helpers, but
is not ok for user-only, where we simply perform the raw memory
operation.

I don't know how to fix this, exactly.  Probably by storing to
tci_tb_ptr before each qemu_ld/qemu_st operation, with barriers.
Then Doing the Right Thing in handle_cpu_signal.  And perhaps
by clearing tci_tb_ptr whenever we're not expecting a SEGV on
behalf of the guest (and thus anything left is a qemu host bug).

---
v2: Retain full struct initialization
---
 tcg/tcg.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/tcg/tcg.c b/tcg/tcg.c
index bbe3dcee03..2991112829 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -513,11 +513,21 @@ static void tcg_region_trees_init(void)
     }
 }
 
-static struct tcg_region_tree *tc_ptr_to_region_tree(const void *cp)
+static struct tcg_region_tree *tc_ptr_to_region_tree(const void *p)
 {
-    void *p = tcg_splitwx_to_rw(cp);
     size_t region_idx;
 
+    /*
+     * Like tcg_splitwx_to_rw, with no assert.  The pc may come from
+     * a signal handler over which the caller has no control.
+     */
+    if (!in_code_gen_buffer(p)) {
+        p -= tcg_splitwx_diff;
+        if (!in_code_gen_buffer(p)) {
+            return NULL;
+        }
+    }
+
     if (p < region.start_aligned) {
         region_idx = 0;
     } else {
@@ -536,6 +546,7 @@ void tcg_tb_insert(TranslationBlock *tb)
 {
     struct tcg_region_tree *rt = tc_ptr_to_region_tree(tb->tc.ptr);
 
+    g_assert(rt != NULL);
     qemu_mutex_lock(&rt->lock);
     g_tree_insert(rt->tree, &tb->tc, tb);
     qemu_mutex_unlock(&rt->lock);
@@ -545,6 +556,7 @@ void tcg_tb_remove(TranslationBlock *tb)
 {
     struct tcg_region_tree *rt = tc_ptr_to_region_tree(tb->tc.ptr);
 
+    g_assert(rt != NULL);
     qemu_mutex_lock(&rt->lock);
     g_tree_remove(rt->tree, &tb->tc);
     qemu_mutex_unlock(&rt->lock);
@@ -561,6 +573,10 @@ TranslationBlock *tcg_tb_lookup(uintptr_t tc_ptr)
     TranslationBlock *tb;
     struct tb_tc s = { .ptr = (void *)tc_ptr };
 
+    if (rt == NULL) {
+        return NULL;
+    }
+
     qemu_mutex_lock(&rt->lock);
     tb = g_tree_lookup(rt->tree, &s);
     qemu_mutex_unlock(&rt->lock);
-- 
2.25.1