linux-kernel - Re: [PATCH] x86/mm: Fix possible index overflow when creating page table mapping

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Message-ID: <3e754cf7-35f8-0163-a24a-063fa3d96718@intel.com>
Date:   Thu, 16 Jun 2022 07:02:56 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yuntao Wang <ytcoode@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, Baoquan He <bhe@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Fix possible index overflow when creating page
 table mapping

On 6/16/22 06:55, Yuntao Wang wrote:
> There are two issues in phys_p4d_init():
> 
> - The __kernel_physical_mapping_init() does not do boundary-checking for
>   paddr_end and passes it directly to phys_p4d_init(), phys_p4d_init() does
>   not do bounds checking either, so if the physical memory to be mapped is
>   large enough, 'p4d_page + p4d_index(vaddr)' will wrap around to the
>   beginning entry of the P4D table and its data will be overwritten.
> 
> - The for loop body will be executed only when 'vaddr < vaddr_end'
>   evaluates to true, but if that condition is true, 'paddr >= paddr_end'
>   will evaluate to false, thus the 'if (paddr >= paddr_end) {}' block will
>   never be executed and become dead code.

Could you explain a bit how you found this?  Was this encountered in
practice and debugged or was it found by inspection?