On 06/07/16 10:54, Stanislav Shmarov wrote:
> 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>
Reviewed-by: Sergey Fedorov <sergey.fedo...@linaro.org>
> ---
> 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);
>
