linux-kernel - Re: [PATCH V3] x86/sgx: Add poison handling to reclaimer

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Date:   Wed, 16 Feb 2022 16:25:24 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     <tony.luck@...el.com>, <dave.hansen@...ux.intel.com>,
        <jarkko@...nel.org>, <tglx@...utronix.de>, <bp@...en8.de>,
        <luto@...nel.org>, <mingo@...hat.com>, <linux-sgx@...r.kernel.org>,
        <x86@...nel.org>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3] x86/sgx: Add poison handling to reclaimer

Dear Maintainers,

On 2/2/2022 11:41 AM, Reinette Chatre wrote:
> The SGX reclaimer code lacks page poison handling in its main
> free path. This can lead to avoidable machine checks if a
> poisoned page is freed and reallocated instead of being
> isolated.
> 
> A troublesome scenario is:
>  1. Machine check (#MC) occurs (asynchronous, !MF_ACTION_REQUIRED)
>  2. arch_memory_failure() is eventually called
>  3. (SGX) page->poison set to 1
>  4. Page is reclaimed
>  5. Page added to normal free lists by sgx_reclaim_pages()
>     ^ This is the bug (poison pages should be isolated on the
>     sgx_poison_page_list instead)
>  6. Page is reallocated by some innocent enclave, a second (synchronous)
>     in-kernel #MC is induced, probably during EADD instruction.
>     ^ This is the fallout from the bug
> 
> (6) is unfortunate and can be avoided by replacing the open coded
> enclave page freeing code in the reclaimer with sgx_free_epc_page()
> to obtain support for poison page handling that includes placing the
> poisoned page on the correct list.
> 
> Fixes: d6d261bded8a ("x86/sgx: Add new sgx_epc_page flag bit to mark free pages")
> Fixes: 992801ae9243 ("x86/sgx: Initial poison handling for dirty and free pages")
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>

Could you please consider this fix for inclusion?

Thank you very much

Reinette