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From: Jarkko Sakkinen <jarkko@kernel.org>
To: Reinette Chatre <reinette.chatre@intel.com>,
	tony.luck@intel.com, dave.hansen@linux.intel.com,
	tglx@linutronix.de, bp@alien8.de, luto@kernel.org,
	mingo@redhat.com, linux-sgx@vger.kernel.org, x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] x86/sgx: Add poison handling to reclaimer
Date: Thu, 20 Jan 2022 15:09:03 +0200	[thread overview]
Message-ID: <3bfe66204ee84a0bbccaf7cd20af0d8300fb9f26.camel@kernel.org> (raw)
In-Reply-To: <be5af586f667c7bcb8ef01286ce75675de5d100f.1642630582.git.reinette.chatre@intel.com>

On Wed, 2022-01-19 at 14:23 -0800, 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")

Same comment as for the first version: remove the first fixes tag.

BR, Jarkko

  reply	other threads:[~2022-01-20 13:09 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-19 22:23 [PATCH V2] x86/sgx: Add poison handling to reclaimer Reinette Chatre
2022-01-20 13:09 ` Jarkko Sakkinen [this message]
2022-01-20 18:20   ` Reinette Chatre
2022-01-22 23:27     ` Jarkko Sakkinen
2022-01-22 23:28       ` Jarkko Sakkinen

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