Richard Henderson <richard.hender...@linaro.org> writes:
> 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. Surely we are asserting that - or at least you can find a rt entry for the pointer passed (which we always expect to work)? > > Fixes: db0c51a3803 > Signed-off-by: Richard Henderson <richard.hender...@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); -- Alex Bennée