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Re: [Qemu-devel] [PATCH v1] i2c: pm_smbus: check smb_index before block
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v1] i2c: pm_smbus: check smb_index before block transfer write |
Date: |
Thu, 6 Dec 2018 08:58:08 -0500 |
On Thu, Dec 06, 2018 at 05:48:30PM +0530, P J P wrote:
> From: Prasad J Pandit <address@hidden>
>
> While performing block transfer write in smb_ioport_writeb(),
> 'smb_index' is incremented and used to index smb_data[] array.
> Check 'smb_index' value to avoid OOB access.
>
> Note that this bug is exploitable by a guest to escape
> from the virtual machine. However the commit which
> introduced the bug was only made after the 3.0 release,
> and so it is not present in any released QEMU versions.
>
> Fixes: 38ad4fae43 i2c: pm_smbus: Add block transfer capability
> Reported-by: Michael Hanselmann <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
Reviewed-by: Michael S. Tsirkin <address@hidden>
> ---
> hw/i2c/pm_smbus.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> Update v1: add note about issue being introduced after 3.0 release
> -> https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg01115.html
>
> diff --git a/hw/i2c/pm_smbus.c b/hw/i2c/pm_smbus.c
> index 685a2378ed..03062740cc 100644
> --- a/hw/i2c/pm_smbus.c
> +++ b/hw/i2c/pm_smbus.c
> @@ -240,6 +240,9 @@ static void smb_ioport_writeb(void *opaque, hwaddr addr,
> uint64_t val,
> uint8_t read = s->smb_addr & 0x01;
>
> s->smb_index++;
> + if (s->smb_index >= PM_SMBUS_MAX_MSG_SIZE) {
> + s->smb_index = 0;
> + }
when I see patterns like these I always think "what about spectre".
But not a new issue and not the only place, so we can leave this
for another day.
> if (!read && s->smb_index == s->smb_data0) {
> uint8_t prot = (s->smb_ctl >> 2) & 0x07;
> uint8_t cmd = s->smb_cmd;
> --
> 2.19.2