From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37790) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bKjy4-00030i-Et for qemu-devel@nongnu.org; Wed, 06 Jul 2016 06:22:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bKjxy-0005XS-E0 for qemu-devel@nongnu.org; Wed, 06 Jul 2016 06:22:07 -0400 Received: from mail-lf0-x22c.google.com ([2a00:1450:4010:c07::22c]:35343) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bKjxy-0005XN-5X for qemu-devel@nongnu.org; Wed, 06 Jul 2016 06:22:02 -0400 Received: by mail-lf0-x22c.google.com with SMTP id l188so151490442lfe.2 for ; Wed, 06 Jul 2016 03:22:01 -0700 (PDT) References: <1467791668-2937838-1-git-send-email-snarpix@gmail.com> From: Sergey Fedorov Message-ID: <577CDBC7.605@linaro.org> Date: Wed, 6 Jul 2016 13:21:59 +0300 MIME-Version: 1.0 In-Reply-To: <1467791668-2937838-1-git-send-email-snarpix@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2] translate-all: Bugfix for user-mode self-modifying code in 2 page long TB List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stanislav Shmarov , qemu-devel@nongnu.org Cc: Paolo Bonzini , Peter Crosthwaite , Richard Henderson 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 Reviewed-by: Sergey Fedorov > --- > 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); >