linux-kernel - Re: [PATCH v2 2/2] platform/x86/amd/pmf: Fix possible out-of-bound memory accesses

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Date: Tue, 27 Feb 2024 17:45:11 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Armin Wolf <W_Armin@....de>, Shyam-sundar.S-k@....com
cc: Hans de Goede <hdegoede@...hat.com>, platform-driver-x86@...r.kernel.org, 
    LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] platform/x86/amd/pmf: Fix possible out-of-bound
 memory accesses

Hi Shyam & Armin,

Shyam, please take a look at the question below.

On Tue, 27 Feb 2024, Armin Wolf wrote:

> The length of the policy buffer is not validated before accessing it,
> which means that multiple out-of-bounds memory accesses can occur.
> 
> This is especially bad since userspace can load policy binaries over
> debugfs.

> +	if (dev->policy_sz < POLICY_COOKIE_LEN + sizeof(length))
> +		return -EINVAL;
> +
>  	cookie = *(u32 *)(dev->policy_buf + POLICY_COOKIE_OFFSET);
>  	length = *(u32 *)(dev->policy_buf + POLICY_COOKIE_LEN);

This starts to feel like adding a struct for the header(?) would be better
course of action here as then one could compare against sizeof(*header) 
and avoid all those casts (IMO, just access the header fields directly 
w/o the local variables).

Shyam, do you think a struct makes sense here? There's some header in 
this policy, right?


There are more thing to address here...

1) amd_pmf_start_policy_engine() function returns -EINVAL & res that is 
   TA_PMF_* which inconsistent in type of the return value

2) Once 1) is fixed, the caller shadowing the return code can be fixed as 
   well:
        ret = amd_pmf_start_policy_engine(dev);
        if (ret)
                return -EINVAL;


-- 
 i.