Re: [PATCH V2] x86/sgx: Add poison handling to reclaimer

[Jarkko Sakkinen]

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