Re: [PATCH] KVM: arm64: Prevent kmemleak from accessing pKVM memory

From: Marc Zyngier <maz@kernel.org>
To: Quentin Perret <qperret@google.com>
Cc: kernel-team@android.com, Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, Mike Rapoport <rppt@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] KVM: arm64: Prevent kmemleak from accessing pKVM memory
Date: Fri, 17 Jun 2022 09:50:44 +0100	[thread overview]
Message-ID: <fa3b5bb1caeaaf98b8a754504c3c9be1@kernel.org> (raw)
In-Reply-To: <Yqw/PI6jF5HZTvxB@google.com>

On 2022-06-17 09:45, Quentin Perret wrote:
> On Friday 17 Jun 2022 at 11:38:14 (+0300), Mike Rapoport wrote:
>> On Fri, Jun 17, 2022 at 09:21:31AM +0100, Marc Zyngier wrote:
>> > On Thu, 16 Jun 2022 16:11:34 +0000, Quentin Perret wrote:
>> > > Commit a7259df76702 ("memblock: make memblock_find_in_range method
>> > > private") changed the API using which memory is reserved for the pKVM
>> > > hypervisor. However, it seems that memblock_phys_alloc() differs
>> > > from the original API in terms of kmemleak semantics -- the old one
>> > > excluded the reserved regions from kmemleak scans when the new one
>> > > doesn't seem to. Unfortunately, when protected KVM is enabled, all
>> > > kernel accesses to pKVM-private memory result in a fatal exception,
>> > > which can now happen because of kmemleak scans:
>> > >
>> > > [...]
>> >
>> > Applied to fixes, thanks!
>> >
>> > [1/1] KVM: arm64: Prevent kmemleak from accessing pKVM memory
>> >       commit: 9e5afa8a537f742bccc2cd91bc0bef4b6483ee98
>> 
>> I'd really like to update the changelog to this:
>> 
>> Commit a7259df76702 ("memblock: make memblock_find_in_range method
>> private") changed the API using which memory is reserved for the pKVM
>> hypervisor. However, memblock_phys_alloc() differs from the original 
>> API in
>> terms of kmemleak semantics -- the old one didn't report the reserved
>> regions to kmemleak while the new one does. Unfortunately, when 
>> protected
>> KVM is enabled, all kernel accesses to pKVM-private memory result in a
>> fatal exception, which can now happen because of kmemleak scans:
>> 
>> $ echo scan > /sys/kernel/debug/kmemleak
>> [   34.991354] kvm [304]: nVHE hyp BUG at: [<ffff800008fa3750>] 
>> __kvm_nvhe_handle_host_mem_abort+0x270/0x290!
>> ...
>> 
>> Fix this by explicitly excluding the hypervisor's memory pool from
>> kmemleak like we already do for the hyp BSS.
> 
> Looks good to me, thanks.

Now updated. Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...
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