From: Wei Liu <wei.liu@kernel.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Sasha Levin <sashal@kernel.org>,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
x86@kernel.org, hpa@zytor.com, mikelley@microsoft.com,
linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@kernel.org, kys@microsoft.com, haiyangz@microsoft.com,
sthemmin@microsoft.com, wei.liu@kernel.org
Subject: Re: [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others()
Date: Thu, 1 Oct 2020 11:53:59 +0000 [thread overview]
Message-ID: <20201001115359.6jhhrybemnhizgok@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <87o8lm9te3.fsf@vitty.brq.redhat.com>
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)
> the check is mandatory indeed. I would, however, just return directly in
> this case:
>
> if (last < num_possible_cpus())
> return;
I think you want
last >= num_possible_cpus()
here?
A more important question is, if the mask can change willy-nilly, what
is stopping it from changing between these checks? I.e. is there still a
windows that hv_cpu_number_to_vp_number(last) can return garbage?
Wei.
>
> if (hv_cpu_number_to_vp_number(last) >= 64)
> goto do_ex_hypercall;
>
> as there's nothing to flush, no need to call into
> hyperv_flush_tlb_others_ex().
>
> Anyway, the fix seems to be correct, so
>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>
> >
> > for_each_cpu(cpu, cpus) {
>
> --
> Vitaly
>
next prev parent reply other threads:[~2020-10-01 11:54 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 1:38 [PATCH] x86/hyper-v: guard against cpu mask changes in hyperv_flush_tlb_others() Sasha Levin
2020-10-01 9:40 ` Vitaly Kuznetsov
2020-10-01 11:53 ` Wei Liu [this message]
2020-10-01 13:04 ` Sasha Levin
2020-10-03 17:40 ` Michael Kelley
2020-10-05 14:58 ` Wei Liu
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
[not found] <VI1PR0401MB24150B31A1D63176BBB788D2F1F19@VI1PR0401MB2415.eurprd04.prod.outlook.com>
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
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