From: Mark Rutland <mark.rutland@arm.com>
To: Evgenii Stepanov <eugenis@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Jisheng Zhang <jszhang@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: extable: fix null deref in load_unaligned_zeropad.
Date: Tue, 25 Jan 2022 15:50:01 +0000 [thread overview]
Message-ID: <YfAcKZpDWmKMZy8q@FVFF77S0Q05N> (raw)
In-Reply-To: <YfAV6FTN5g6jZGj7@FVFF77S0Q05N>
On Tue, Jan 25, 2022 at 03:23:20PM +0000, Mark Rutland wrote:
> On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote:
> > ex_handler_load_unaligned_zeropad extracts the source and data register
> > numbers from the wrong field of the exception table.
>
> Ouch. Did you find this by inspection, or did this show up in testing?
>
> Sorry about this.
>
> I think we should be a little more explicit as to exactly what goes wrong. How
> about:
>
> | In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
> | addr register indices from ex->type rather than ex->data. As ex->type will
> | contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
> |
> | * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
> | extracted from bits [9:5]. Thus, we may attempt to dereference an arbitrary
> | address as X0 may hold an arbitary value.
> |
> | * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
> | extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
> | behaviour within load_unaligned_zeropad() and its caller.
> |
> | Fix this by extracting both values from ex->data as originally intended.
>
> > Fixes: 753b3236
>
> That should be expanded, e.g.
>
> Fixes: 753b32368705c396 ("arm64: extable: add load_unaligned_zeropad() handler")
>
> With those changes:
>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Looking again, sicne this isn't jsut a null-deref, can we also rework the
title, something like:
| arm64: extable: fix load_unaligned_zeropad() reg indices
Thanks,
Mark.
next prev parent reply other threads:[~2022-01-25 15:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-22 2:34 [PATCH] arm64: extable: fix null deref in load_unaligned_zeropad Evgenii Stepanov
2022-01-24 9:56 ` Catalin Marinas
2022-01-25 15:23 ` Mark Rutland
2022-01-25 15:50 ` Mark Rutland [this message]
2022-01-25 16:59 ` Evgenii Stepanov
2022-01-25 17:07 ` Mark Rutland
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