From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38135) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aTZg2-0005Fd-ET for qemu-devel@nongnu.org; Wed, 10 Feb 2016 13:39:47 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aTZfz-00057t-5A for qemu-devel@nongnu.org; Wed, 10 Feb 2016 13:39:46 -0500 Received: from mout.kundenserver.de ([217.72.192.73]:51782) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aTZfy-00057g-Ry for qemu-devel@nongnu.org; Wed, 10 Feb 2016 13:39:43 -0500 References: <1455033431-24034-1-git-send-email-peter.maydell@linaro.org> From: Laurent Vivier Message-ID: <56BB83E2.10108@vivier.eu> Date: Wed, 10 Feb 2016 19:39:30 +0100 MIME-Version: 1.0 In-Reply-To: <1455033431-24034-1-git-send-email-peter.maydell@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] linux-user: Don't assert if guest tries shmdt(0) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell , qemu-devel@nongnu.org Cc: Pavel Shamis , Riku Voipio , patches@linaro.org Le 09/02/2016 16:57, Peter Maydell a écrit : > Our implementation of shmat() and shmdt() for linux-user was > using "zero guest address" as its marker for "entry in the > shm_regions[] array is not in use". This meant that if the > guest did a shmdt(0) we would match on an unused array entry Is shmdt(0) valid ? I mean, if shmat() is called with shmaddr equal to 0: "the system chooses a suitable (unused) address at which to attach the segment." and "The to-be-detached segment must be currently attached with shmaddr equal to the value returned by the attaching shmat() call." Did you check shmat() can return 0 ? (I think our mmap_find_vma() cannot return 0) Why don't you fail on shmdt(0) (EINVAL) ? > and call page_set_flags() with both start and end addresses zero, > which causes an assertion failure. > > Use an explicit in_use flag to manage the shm_regions[] array, > so that we avoid this problem. > > Signed-off-by: Peter Maydell > Reported-by: Pavel Shamis > --- > linux-user/syscall.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/linux-user/syscall.c b/linux-user/syscall.c > index 54ce14a..f46abf7 100644 > --- a/linux-user/syscall.c > +++ b/linux-user/syscall.c > @@ -2598,8 +2598,9 @@ static abi_long do_socketcall(int num, abi_ulong vptr) > #define N_SHM_REGIONS 32 > > static struct shm_region { > - abi_ulong start; > - abi_ulong size; > + abi_ulong start; > + abi_ulong size; > + bool in_use; > } shm_regions[N_SHM_REGIONS]; > > struct target_semid_ds > @@ -3291,7 +3292,8 @@ static inline abi_ulong do_shmat(int shmid, abi_ulong shmaddr, int shmflg) > ((shmflg & SHM_RDONLY)? 0 : PAGE_WRITE)); > > for (i = 0; i < N_SHM_REGIONS; i++) { > - if (shm_regions[i].start == 0) { > + if (!shm_regions[i].in_use) { > + shm_regions[i].in_use = true; > shm_regions[i].start = raddr; > shm_regions[i].size = shm_info.shm_segsz; > break; > @@ -3308,8 +3310,8 @@ static inline abi_long do_shmdt(abi_ulong shmaddr) > int i; > > for (i = 0; i < N_SHM_REGIONS; ++i) { > - if (shm_regions[i].start == shmaddr) { > - shm_regions[i].start = 0; > + if (shm_regions[i].in_use && shm_regions[i].start == shmaddr) { > + shm_regions[i].in_use = false; > page_set_flags(shmaddr, shmaddr + shm_regions[i].size, 0); > break; > } >