From 0f0fcbdbffaa27a1419d03eef12f4d5d4e474375 Mon Sep 17 00:00:00 2001 From: Reinette Chatre Date: Wed, 2 Feb 2022 11:41:12 -0800 Subject: [PATCH] x86/sgx: Fix missing poison handling in reclaimer 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: 5aa8b3e7cf7c ("x86/sgx: Add new sgx_epc_page flag bit to mark free pages") Fixes: a1500f0d2d28 ("x86/sgx: Initial poison handling for dirty and free pages") Signed-off-by: Reinette Chatre Signed-off-by: Dave Hansen Reviewed-by: Jarkko Sakkinen Link: https://lkml.kernel.org/r/dcc95eb2aaefb042527ac50d0a50738c7c160dac.1643830353.git.reinette.chatre@intel.com --- arch/x86/kernel/cpu/sgx/main.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c index 4b41efc9e367a..8e4bc6453d263 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -344,10 +344,8 @@ static void sgx_reclaim_pages(void) { struct sgx_epc_page *chunk[SGX_NR_TO_SCAN]; struct sgx_backing backing[SGX_NR_TO_SCAN]; - struct sgx_epc_section *section; struct sgx_encl_page *encl_page; struct sgx_epc_page *epc_page; - struct sgx_numa_node *node; pgoff_t page_index; int cnt = 0; int ret; @@ -418,13 +416,7 @@ skip: kref_put(&encl_page->encl->refcount, sgx_encl_release); epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED; - section = &sgx_epc_sections[epc_page->section]; - node = section->node; - - spin_lock(&node->lock); - list_add_tail(&epc_page->list, &node->free_page_list); - spin_unlock(&node->lock); - atomic_long_inc(&sgx_nr_free_pages); + sgx_free_epc_page(epc_page); } } -- 2.39.5