From: Christoph Hellwig <hch@lst.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>, Dexuan Cui <decui@microsoft.com>,
vkuznets <vkuznets@redhat.com>,
Stephen Hemminger <stephen@networkplumber.org>,
Andy Lutomirski <luto@kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Michael Kelley <mikelley@microsoft.com>,
Ju-Hyoung Lee <juhlee@microsoft.com>,
"x86@kernel.org" <x86@kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
KY Srinivasan <kys@microsoft.com>,
Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: hv_hypercall_pg page permissios
Date: Tue, 16 Jun 2020 12:24:12 +0200 [thread overview]
Message-ID: <20200616102412.GB29684@lst.de> (raw)
In-Reply-To: <20200616102350.GA29684@lst.de>
On Tue, Jun 16, 2020 at 12:23:50PM +0200, Christoph Hellwig wrote:
> On Tue, Jun 16, 2020 at 12:18:07PM +0200, Peter Zijlstra wrote:
> > > It does. But it also means every other user of PAGE_KERNEL_EXEC
> > > should trigger this, of which there are a few (kexec, tboot, hibernate,
> > > early xen pv mapping, early SEV identity mapping)
> >
> > There are only 3 users in the entire tree afaict:
> >
> > arch/arm64/kernel/probes/kprobes.c: page = vmalloc_exec(PAGE_SIZE);
> > arch/x86/hyperv/hv_init.c: hv_hypercall_pg = vmalloc_exec(PAGE_SIZE);
> > kernel/module.c: return vmalloc_exec(size);
> >
> > And that last one is a weak function that any arch that has STRICT_RWX
> > ought to override.
> >
> > > We really shouldn't create mappings like this by default. Either we
> > > need to flip PAGE_KERNEL_EXEC itself based on the needs of the above
> > > users, or add another define to overload vmalloc_exec as there is no
> > > other user of that for x86.
> >
> > We really should get rid of the two !module users of this though; both
> > x86 and arm64 have STRICT_RWX and sufficient primitives to DTRT.
> >
> > What is HV even trying to do with that page? AFAICT it never actually
> > writes to it, it seens to give the physica address to an MSR (which I
> > suspect then writes crud into the page for us from host context).
> >
> > Suggesting the page really only needs to be RX.
> >
> > On top of that, vmalloc_exec() gets us a page from the entire vmalloc
> > range, which can be outside of the 2G executable range, which seems to
> > suggest vmalloc_exec() is wrong too and all this works by accident.
> >
> > How about something like this:
> >
> >
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index a54c6a401581..82a3a4a9481f 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -375,12 +375,15 @@ void __init hyperv_init(void)
> > guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
> > wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
> >
> > - hv_hypercall_pg = vmalloc_exec(PAGE_SIZE);
> > + hv_hypercall_pg = module_alloc(PAGE_SIZE);
> > if (hv_hypercall_pg == NULL) {
> > wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
> > goto remove_cpuhp_state;
> > }
> >
> > + set_memory_ro((unsigned long)hv_hypercall_pg, 1);
> > + set_memory_x((unsigned long)hv_hypercall_pg, 1);
>
> The changing of the permissions sucks. I thought about adding
> a module_alloc_prot with an explicit pgprot_t argument. On x86
> alone at least ftrace would also benefit from that.
The above is also missing a set_vm_flush_reset_perms.
next prev parent reply other threads:[~2020-06-16 10:24 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-07 6:55 hv_hypercall_pg page permissios Christoph Hellwig
2020-04-07 7:28 ` Vitaly Kuznetsov
2020-04-07 7:38 ` Christoph Hellwig
2020-04-07 21:01 ` Andy Lutomirski
2020-06-12 7:48 ` Dexuan Cui
2020-06-15 8:35 ` Vitaly Kuznetsov
2020-06-15 17:41 ` Dexuan Cui
2020-06-15 19:49 ` Dexuan Cui
2020-06-16 7:23 ` Christoph Hellwig
2020-06-16 10:18 ` Peter Zijlstra
2020-06-16 10:23 ` Christoph Hellwig
2020-06-16 10:24 ` Christoph Hellwig [this message]
2020-06-16 10:31 ` Peter Zijlstra
2020-06-16 10:33 ` Christoph Hellwig
2020-06-16 10:40 ` Peter Zijlstra
2020-06-16 10:42 ` Christoph Hellwig
2020-06-16 10:52 ` Christoph Hellwig
2020-06-16 11:24 ` Peter Zijlstra
2020-06-16 14:39 ` Christoph Hellwig
2020-06-16 9:29 ` Vitaly Kuznetsov
2020-06-16 9:33 ` Christoph Hellwig
2020-06-16 9:55 ` Christoph Hellwig
2020-06-16 10:08 ` Christoph Hellwig
2020-06-16 10:50 ` Vitaly Kuznetsov
2020-06-16 10:20 ` Peter Zijlstra
2020-04-07 18:10 ` Dexuan Cui
2020-04-07 20:42 ` Wei Liu
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