From: joel.schopp@amd•com (Joel Schopp)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v3] arm64: fix VTTBR_BADDR_MASK
Date: Mon, 11 Aug 2014 15:21:41 -0500 [thread overview]
Message-ID: <53E925D5.4050102@amd.com> (raw)
In-Reply-To: <20140811191938.GJ10550@cbox>
>>> That said, I don't think this is doing the right thing. I think you
>>> want to refuse running the VM and avoid any stage-2 entried being
>>> created if this is not the case (actually, we may want to check this
>>> after set_vttbr_baddr_mask() or right aftert allocating the stage-2
>>> pgd), because otherwise I think we may be overwriting memory not
>>> belonging to us with concatenated page tables in a 42-bit 4KB system,
>>> for example.
>> My experience here was that the hardware actually catches the error on
>> the first instruction load of the guest kernel and does a stage 2
>> translation abort. However, to be extra safe we could just log the
>> error with the address of the vttbr and then zero out the pgd_phys part
>> of vttbr altogether, leaving only the vmid. The guest would then die of
>> natural causes and we wouldn't have to worry about the outside
>> possibility of memory getting overwritten.
> uh, putting zero in the pgd_phys part will just point to random memory
> if you happen to have memory based at address 0 though, right?
>
> I think we should check when we allocate the pgd that it is indeed of
> the right size and alignment, and if it isn't at this point, it truly is
> a BUG() and your kernel is terribly busted.
If I can't rely on 0 to be an invalid address I can't think of what I
could rely on to be invalid. I'll just change this to BUG_ON(pgd_phys &
~vttbr_baddr_mask); and give up on my dream of the host kernel surviving
the bug.
prev parent reply other threads:[~2014-08-11 20:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-04 14:38 [PATCH v3] arm64: fix VTTBR_BADDR_MASK Joel Schopp
2014-08-04 14:42 ` Joel Schopp
2014-08-04 15:18 ` Christoffer Dall
2014-08-08 20:46 ` Christoffer Dall
2014-08-11 15:20 ` Joel Schopp
2014-08-11 19:19 ` Christoffer Dall
2014-08-11 20:21 ` Joel Schopp [this message]
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