linux-hyperv.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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
> 

  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 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

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=20201001115359.6jhhrybemnhizgok@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).