linux-kernel - Re: potential null pointer dereference in setup_cpuid

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Message-ID: <20230807205746.GJZNFaytU85YvQCd3C@fat_crate.local>
Date:   Mon, 7 Aug 2023 22:57:46 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Colin King (gmail)" <colin.i.king@...il.com>
Cc:     Michael Roth <michael.roth@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: potential null pointer dereference in setup_cpuid_table

On Thu, Jul 27, 2023 at 03:22:42PM +0100, Colin King (gmail) wrote:
> Hi,
> 
> Static analysis with cppcheck found a potential null pointer dereference in
> function setup_cpuid_table in arch/x86/kernel/sev-shared.c as follows:
> 
>         if (!cc_info || !cc_info->cpuid_phys || cc_info->cpuid_len <
> PAGE_SIZE)
>                 sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);
> 
>         cpuid_table_fw = (const struct snp_cpuid_table
> *)cc_info->cpuid_phys;
> 
> 
> cc_info is being null checked, so it's potentially null,

You mean, it is not null if the check passes?

> however, the assignment to cpuid_table_fw is dereferencing cc_info.
> Either cc_info is never null and the null check is redundant, or there
> is a potential null pointer dereference.

I'm not sure what you're asking. It is checked for !NULL in the if
clause.

Or are you missing the fact that sev_es_terminate() actually terminates
the guest so that if it is NULL, it won't ever be dereferenced?

Or am I missing something?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette