In user-mode emulation Translation Block can consist of 2 guest pages.
In that case QEMU also mprotects 2 host pages that are dedicated for
guest memory, containing instructions. QEMU detects self-modifying code
with SEGFAULT signal processing.
In case if instruction in 1st page is modifying memory of 2nd
page (or vice versa) QEMU will mark 2nd page with PAGE_WRITE,
invalidate TB, generate new TB contatining 1 guest instruction and
exit to CPU loop. QEMU won't call mprotect, and new TB will cause
same SEGFAULT. Page will have both PAGE_WRITE_ORG and PAGE_WRITE
flags, so QEMU will handle the signal as guest binary problem,
and exit with guest SEGFAULT.
Solution is retranslate TB before marking pages as PAGE_WRITE,
and remove protection with mprotect on second SEGFAULT.
Signed-off-by: Stanislav Shmarov <snar...@gmail.com>
---
v2: Moved setting PAGE_WRITE flag to separte loop, to cover cases,
pointed by Sergey Fedorov.
translate-all.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/translate-all.c b/translate-all.c
index eaa95e4..fb3743f 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -2020,13 +2020,8 @@ int page_unprotect(target_ulong address, uintptr_t pc)
host_start = address & qemu_host_page_mask;
host_end = host_start + qemu_host_page_size;
- prot = 0;
for (addr = host_start ; addr < host_end ; addr += TARGET_PAGE_SIZE) {
- p = page_find(addr >> TARGET_PAGE_BITS);
- p->flags |= PAGE_WRITE;
- prot |= p->flags;
-
- /* and since the content will be modified, we must invalidate
+ /* Since the content will be modified, we must invalidate
the corresponding translated code. */
if (tb_invalidate_phys_page(addr, pc)) {
mmap_unlock();
@@ -2036,6 +2031,16 @@ int page_unprotect(target_ulong address, uintptr_t pc)
tb_invalidate_check(addr);
#endif
}
+
+ /* If we got here, current TB have been retranslated (in case of
+ * self-modifying code), now it's safe to remove page protection.
+ */
+ prot = 0;
+ for (addr = host_start ; addr < host_end ; addr += TARGET_PAGE_SIZE) {
+ p = page_find(addr >> TARGET_PAGE_BITS);
+ p->flags |= PAGE_WRITE;
+ prot |= p->flags;
+ }
mprotect((void *)g2h(host_start), qemu_host_page_size,
prot & PAGE_BITS);
--
1.9.3
