linux-kernel - Re: [PATCH] libata: Avoid overflow in ata_tf_to_lba48() when tf->hba

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Message-ID: <7a9b5c320810290628q615285gb3b67230776ab4e1@mail.gmail.com>
Date:	Thu, 30 Oct 2008 02:28:16 +1300
From:	"Phillip O'Donnell" <phillip.odonnell@...il.com>
To:	"Roland Dreier" <rdreier@...co.com>
Cc:	jeff@...zik.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libata: Avoid overflow in ata_tf_to_lba48() when tf->hba_lbal > 127

Confirmed - HPA is no longer detected on boot.

Cheers,
Phillip

On Wed, Oct 29, 2008 at 12:52 PM, Roland Dreier <rdreier@...co.com> wrote:
> In ata_tf_to_lba48(), when evaluating
>
>        (tf->hob_lbal & 0xff) << 24
>
> the expression is promoted to signed int (since int can hold all values
> of u8).  However, if hob_lbal is 128 or more, then it is treated as a
> negative signed value and sign-extended when promoted to u64 to | into
> sectors, which leads to the MSB 32 bits of section getting set
> incorrectly.
>
> For example, Phillip O'Donnell <phillip.odonnell@...il.com> reported
> that a 1.5GB drive caused:
>
>    ata3.00: HPA detected: current 2930277168, native 18446744072344861488
>
> where 2930277168 == 0xAEA87B30 and 18446744072344861488 == 0xffffffffaea87b30
> which shows the problem when hob_lbal is 0xae.
>
> Fix this by adding a cast to u64, just as is used by for hob_lbah and
> hob_lbam in the function.
>
> Reported-by: Phillip O'Donnell <phillip.odonnell@...il.com>
> Signed-off-by: Roland Dreier <rolandd@...co.com>
> ---
> Phillip, this should fix at least your cosmetic issue; can you test it
> and report back?
>
> Thanks,
>  Roland
>
>  drivers/ata/libata-core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index bbb3cae..10424ff 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -1268,7 +1268,7 @@ u64 ata_tf_to_lba48(const struct ata_taskfile *tf)
>
>        sectors |= ((u64)(tf->hob_lbah & 0xff)) << 40;
>        sectors |= ((u64)(tf->hob_lbam & 0xff)) << 32;
> -       sectors |= (tf->hob_lbal & 0xff) << 24;
> +       sectors |= ((u64)(tf->hob_lbal & 0xff)) << 24;
>        sectors |= (tf->lbah & 0xff) << 16;
>        sectors |= (tf->lbam & 0xff) << 8;
>        sectors |= (tf->lbal & 0xff);
>
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