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authorReinette Chatre <reinette.chatre@intel.com>2022-02-02 11:41:12 -0800
committerDave Hansen <dave.hansen@linux.intel.com>2022-02-17 10:24:50 -0800
commite5733d8c89c3b57c8fcd40b8acf508388fabaa42 (patch)
tree5446223bcbf580ed0cfb60b3a6c052b10bc28faf
parent8795359e35bc33bf86b6d0765aa7f37431db3b9c (diff)
downloadlwn-e5733d8c89c3b57c8fcd40b8acf508388fabaa42.tar.gz
lwn-e5733d8c89c3b57c8fcd40b8acf508388fabaa42.zip
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: 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") Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> Link: https://lkml.kernel.org/r/dcc95eb2aaefb042527ac50d0a50738c7c160dac.1643830353.git.reinette.chatre@intel.com
-rw-r--r--arch/x86/kernel/cpu/sgx/main.c10
1 files changed, 1 insertions, 9 deletions
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 4b41efc9e367..8e4bc6453d26 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);
}
}