h2g() will assert if passed an address that's not a valid guest address,
so handle_cpu_signal() needs to check before passing "data address
which caused a segfault" to it, since for a misbehaving guest
that could be anything. If the address isn't a valid guest address
then we can simply skip the attempt to unprotect a guest page
which was made read-only to catch self-modifying code.
This assertion probably fires more readily now than it used to
do because of recent changes to default to reserving guest address
space.
Signed-off-by: Peter Maydell<address@hidden>
---
I've tentatively marked this as for-1.1 as it's pretty safe, although
it doesn't buy you a great deal: misbehaving guest binaries will
die cleanly with a segfault rather than qemu asserting and then
locking up (assert() in qemu's linux-user code doesn't really behave
very nicely...)
user-exec.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/user-exec.c b/user-exec.c
index be6bc4f..d8c2ad9 100644
--- a/user-exec.c
+++ b/user-exec.c
@@ -97,7 +97,8 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned
long address,
pc, address, is_write, *(unsigned long *)old_set);
#endif
/* XXX: locking issue */
- if (is_write&& page_unprotect(h2g(address), pc, puc)) {
+ if (is_write&& h2g_valid(address)
+&& page_unprotect(h2g(address), pc, puc)) {
return 1;
}