LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Wei Liu <wei.liu@kernel.org>
To: Michael Kelley <mikelley@microsoft.com>
Cc: Sasha Levin <sashal@kernel.org>, Wei Liu <wei.liu@kernel.org>,
	vkuznets <vkuznets@redhat.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"bp@alien8.de" <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stable@kernel.org" <stable@kernel.org>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>
Subject: Re: [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others()
Date: Mon, 5 Oct 2020 14:58:51 +0000	[thread overview]
Message-ID: <20201005145851.hdyaeqo3celt2wtr@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <MW2PR2101MB105242653A8D5C7DD9DF1062D70E0@MW2PR2101MB1052.namprd21.prod.outlook.com>

On Sat, Oct 03, 2020 at 05:40:15PM +0000, Michael Kelley wrote:
> From: Sasha Levin <sashal@kernel.org>  Sent: Thursday, October 1, 2020 6:04 AM
> > 
> > On Thu, Oct 01, 2020 at 11:53:59AM +0000, Wei Liu wrote:
> > >On Thu, Oct 01, 2020 at 11:40:04AM +0200, Vitaly Kuznetsov wrote:
> > >> Sasha Levin <sashal@kernel.org> writes:
> > >>
> > >> > cpumask can change underneath us, which is generally safe except when we
> > >> > call into hv_cpu_number_to_vp_number(): if cpumask ends up empty we pass
> > >> > num_cpu_possible() into hv_cpu_number_to_vp_number(), causing it to read
> > >> > garbage. As reported by KASAN:
> > >> >
> > >> > [   83.504763] BUG: KASAN: slab-out-of-bounds in hyperv_flush_tlb_others
> > (include/asm-generic/mshyperv.h:128 arch/x86/hyperv/mmu.c:112)
> > >> > [   83.908636] Read of size 4 at addr ffff888267c01370 by task kworker/u8:2/106
> > >> > [   84.196669] CPU: 0 PID: 106 Comm: kworker/u8:2 Tainted: G        W         5.4.60 #1
> > >> > [   84.196669] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine,
> > BIOS 090008  12/07/2018
> > >> > [   84.196669] Workqueue: writeback wb_workfn (flush-8:0)
> > >> > [   84.196669] Call Trace:
> > >> > [   84.196669] dump_stack (lib/dump_stack.c:120)
> > >> > [   84.196669] print_address_description.constprop.0 (mm/kasan/report.c:375)
> > >> > [   84.196669] __kasan_report.cold (mm/kasan/report.c:507)
> > >> > [   84.196669] kasan_report (arch/x86/include/asm/smap.h:71
> > mm/kasan/common.c:635)
> > >> > [   84.196669] hyperv_flush_tlb_others (include/asm-generic/mshyperv.h:128
> > arch/x86/hyperv/mmu.c:112)
> > >> > [   84.196669] flush_tlb_mm_range (arch/x86/include/asm/paravirt.h:68
> > arch/x86/mm/tlb.c:798)
> > >> > [   84.196669] ptep_clear_flush (arch/x86/include/asm/tlbflush.h:586 mm/pgtable-
> > generic.c:88)
> > >> >
> > >> > Fixes: 0e4c88f37693 ("x86/hyper-v: Use cheaper
> > HVCALL_FLUSH_VIRTUAL_ADDRESS_{LIST,SPACE} hypercalls when possible")
> > >> > Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> > >> > Cc: stable@kernel.org
> > >> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > >> > ---
> > >> >  arch/x86/hyperv/mmu.c | 4 +++-
> > >> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >> >
> > >> > diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
> > >> > index 5208ba49c89a9..b1d6afc5fc4a3 100644
> > >> > --- a/arch/x86/hyperv/mmu.c
> > >> > +++ b/arch/x86/hyperv/mmu.c
> > >> > @@ -109,7 +109,9 @@ static void hyperv_flush_tlb_others(const struct cpumask
> > *cpus,
> > >> >  		 * must. We will also check all VP numbers when walking the
> > >> >  		 * supplied CPU set to remain correct in all cases.
> > >> >  		 */
> > >> > -		if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64)
> > >> > +		int last = cpumask_last(cpus);
> > >> > +
> > >> > +		if (last < num_possible_cpus() && hv_cpu_number_to_vp_number(last) >=
> > 64)
> > >> >  			goto do_ex_hypercall;
> > >>
> > >> In case 'cpus' can end up being empty (I'm genuinely suprised it can)
> > 
> > I was just as surprised as you and spent the good part of a day
> > debugging this. However, a:
> > 
> > 	WARN_ON(cpumask_empty(cpus));
> > 
> > triggers at that line of code even though we check for cpumask_empty()
> > at the entry of the function.
> 
> What does the call stack look like when this triggers?  I'm curious about
> the path where the 'cpus' could be changing while the flush call is in
> progress.
> 
> I wonder if CPUs could ever be added to the mask?  Removing CPUs can
> be handled with some care because an unnecessary flush doesn't hurt
> anything.   But adding CPUs has serious correctness problems.
> 

The cpumask_empty check is done before disabling irq. Is it possible
the mask is modified by an interrupt?

If there is a reliable way to trigger this bug, we may be able to test
the following patch.

diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
index 5208ba49c89a..23fa08d24c1a 100644
--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -66,11 +66,13 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,
        if (!hv_hypercall_pg)
                goto do_native;

-       if (cpumask_empty(cpus))
-               return;
-
        local_irq_save(flags);

+       if (cpumask_empty(cpus)) {
+               local_irq_restore(flags);
+               return;
+       }
+
        flush_pcpu = (struct hv_tlb_flush **)
                     this_cpu_ptr(hyperv_pcpu_input_arg);


  reply	other threads:[~2020-10-05 14:58 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01  1:38 Sasha Levin
2020-10-01  9:40 ` Vitaly Kuznetsov
2020-10-01 11:53   ` Wei Liu
2020-10-01 13:04     ` Sasha Levin
2020-10-03 17:40       ` Michael Kelley
2020-10-05 14:58         ` Wei Liu [this message]
2021-01-05 16:59           ` Michael Kelley
2021-01-05 17:10             ` Wei Liu
2021-01-08 15:22             ` Sasha Levin
2020-10-01 13:10     ` Vitaly Kuznetsov
2021-08-04 11:23 David Mozes
2021-08-05 18:08 ` Michael Kelley
     [not found] <CA+qYZY3a-FHfWNL2=na6O8TRJYu9kaeyp80VNDxaDTi2EBGoog@mail.gmail.com>
2021-08-06 10:43 ` Michael Kelley
2021-08-06 17:35   ` David Mozes
     [not found]     ` <CAHkVu0-ZCXDRZL92d_G3oKpPuKvmY=YEbu9nbx9vkZHnhHFD8Q@mail.gmail.com>
2021-08-06 21:51       ` Michael Kelley
2021-08-07  5:00         ` David Moses
2021-08-17  9:16           ` David Mozes
2021-08-17 11:29             ` Wei Liu
2021-08-19 11:05               ` David Mozes
     [not found]               ` <CA+qYZY1U04SkyHo7X+rDeE=nUy_X5nxLfShyuLJFzXnFp2A6uw@mail.gmail.com>
     [not found]                 ` <VI1PR0401MB24153DEC767B0126B1030E07F1C09@VI1PR0401MB2415.eurprd04.prod.outlook.com>
2021-08-22 15:24                   ` Wei Liu
2021-08-22 16:25                     ` David Mozes
2021-08-22 17:32                       ` Wei Liu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201005145851.hdyaeqo3celt2wtr@liuwe-devbox-debian-v2 \
    --to=wei.liu@kernel.org \
    --cc=bp@alien8.de \
    --cc=haiyangz@microsoft.com \
    --cc=hpa@zytor.com \
    --cc=kys@microsoft.com \
    --cc=linux-hyperv@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mikelley@microsoft.com \
    --cc=mingo@redhat.com \
    --cc=sashal@kernel.org \
    --cc=stable@kernel.org \
    --cc=sthemmin@microsoft.com \
    --cc=tglx@linutronix.de \
    --cc=vkuznets@redhat.com \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others()' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).