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Message-ID: <8e2c9b2b-d8ad-5e9a-7aa6-23e0c599c2e9@intel.com>
Date:   Thu, 16 Jun 2022 07:20:40 -0700
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Subject: Re: [PATCH] x86/mm: Fix possible index overflow when creating page
 table mapping
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To:     Yuntao Wang <ytcoode@gmail.com>
Cc:     bhe@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, kirill@shutemov.name, linux-kernel@vger.kernel.org,
        luto@kernel.org, mingo@redhat.com, peterz@infradead.org,
        stable@vger.kernel.org, tglx@linutronix.de, x86@kernel.org
References: <3e754cf7-35f8-0163-a24a-063fa3d96718@intel.com>
 <20220616141525.1790083-1-ytcoode@gmail.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20220616141525.1790083-1-ytcoode@gmail.com>
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On 6/16/22 07:15, Yuntao Wang wrote:
> On Thu, 16 Jun 2022 07:02:56 -0700, Dave Hansen wrote:
>> 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?
> I found it by inspection.

Dare I ask how this was tested?