linux-kernel - Re: [PATCH 02/16] KVM: arm64: Don't issue CMOs when the physical address is invalid

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YPWzykpDMOhT2yh8@google.com>
Date:   Mon, 19 Jul 2021 18:18:02 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org, will@...nel.org,
        dbrazdil@...gle.com, Srivatsa Vaddagiri <vatsa@...eaurora.org>,
        Shanker R Donthineni <sdonthineni@...dia.com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH 02/16] KVM: arm64: Don't issue CMOs when the physical
 address is invalid

On Thursday 15 Jul 2021 at 17:31:45 (+0100), Marc Zyngier wrote:
> Make sure we don't issue CMOs when mapping something that
> is not a memory address in the S2 page tables.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  arch/arm64/kvm/hyp/pgtable.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 05321f4165e3..a5874ebd0354 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -619,12 +619,16 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
>  	}
>  
>  	/* Perform CMOs before installation of the guest stage-2 PTE */
> -	if (mm_ops->dcache_clean_inval_poc && stage2_pte_cacheable(pgt, new))
> -		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(new, mm_ops),
> -						granule);
> -
> -	if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
> -		mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule);
> +	if (kvm_phys_is_valid(phys)) {
> +		if (mm_ops->dcache_clean_inval_poc &&
> +		    stage2_pte_cacheable(pgt, new))
> +			mm_ops->dcache_clean_inval_poc(kvm_pte_follow(new,
> +								      mm_ops),
> +						       granule);
> +		if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
> +			mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops),
> +						 granule);
> +	}

Hrmpf so this makes me realize we have a problem here, not really caused
by your patch though.

Specifically, calling kvm_pgtable_stage2_set_owner() can lead to
overriding valid mappings with invalid mappings, which is effectively an
unmap operation. In this case we should issue CMOs when unmapping a
cacheable page to ensure it is clean to the PoC, like the
kvm_pgtable_stage2_unmap() does.

Note that you patch is already an improvement over the current state of
things, because calling stage2_pte_cacheable(pgt, new),
kvm_pte_follow(new, mm_ops) and friends is bogus when 'new' is invalid
...

Thanks,
Quentin