From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49391) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cRas5-0000B7-FA for qemu-devel@nongnu.org; Thu, 12 Jan 2017 03:36:35 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cRas0-0001ID-Tm for qemu-devel@nongnu.org; Thu, 12 Jan 2017 03:36:33 -0500 References: <1484167250-16089-1-git-send-email-thuth@redhat.com> <87tw94em1e.fsf@dusky.pond.sub.org> From: Thomas Huth Message-ID: Date: Thu, 12 Jan 2017 09:36:25 +0100 MIME-Version: 1.0 In-Reply-To: <87tw94em1e.fsf@dusky.pond.sub.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] monitor: Fix crashes when using HMP commands without CPU List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , qemu-trivial@nongnu.org On 12.01.2017 09:10, Markus Armbruster wrote: > Thomas Huth writes: >=20 >> When running certain HMP commands ("info registers", "info cpustats" >> or dumping virtual memory) with the "none" machine, QEMU crashes >> with a segmentation fault. This happens because the "none" machine doe= s >> not have any CPUs by default, >=20 > "Sachen gibt's!" >=20 >> but these HMP commands did not check for >> a valid CPU pointer yet. Add such a check now and print a message >> about the missing CPU instead. >=20 > Have you checked uses of first_cpu elsewhere? Out of scope for this > patch, of course. I only looked at monitor.c so far, and that's the only spot that uses this variable there. But it seems like gdbstub.c has the same bug, too. If I start the "none" machine and attach a remote gdb, QEMU segfaults here, too. I've put this on my TODO-list... (I think it should be fixed with a separate patch). >> Signed-off-by: Thomas Huth >> --- >> monitor.c | 29 +++++++++++++++++++++++++---- >> 1 file changed, 25 insertions(+), 4 deletions(-) >> >> diff --git a/monitor.c b/monitor.c >> index 0841d43..0103979 100644 >> --- a/monitor.c >> +++ b/monitor.c >> @@ -1025,6 +1025,9 @@ int monitor_set_cpu(int cpu_index) >> CPUState *mon_get_cpu(void) >> { >> if (!cur_mon->mon_cpu) { >> + if (!first_cpu) { >> + return NULL; >> + } >> monitor_set_cpu(first_cpu->cpu_index); >> } >> cpu_synchronize_state(cur_mon->mon_cpu); >=20 > Why are the following dereferences safe? >=20 > CPUArchState *mon_get_cpu_env(void) > { > return mon_get_cpu()->env_ptr; > } >=20 > int monitor_get_cpu_index(void) > { > return mon_get_cpu()->cpu_index; > } Oh, they are apparently not safe either. The HMP commands "nmi" and "memsave", which use these functions, are crashing on the "none" machine, too... I'll send a v2 of my patch to fix these, too ... Thanks for the review! Thomas