| Message ID | dcc95eb2aaefb042527ac50d0a50738c7c160dac.1643830353.git.reinette.chatre@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V3] x86/sgx: Add poison handling to reclaimer | expand |
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@kernel.org> > Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> Could you please consider this fix for inclusion? Thank you very much Reinette
On 2/16/22 16:25, Reinette Chatre wrote: >> 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@kernel.org> >> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> > Could you please consider this fix for inclusion? Thanks for the reminder. It's merged here: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/urgent&id=e5733d8c89c3b5
On 2/17/2022 10:26 AM, Dave Hansen wrote: > On 2/16/22 16:25, Reinette Chatre wrote: >>> 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@kernel.org> >>> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> >> Could you please consider this fix for inclusion? > > Thanks for the reminder. It's merged here: > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/urgent&id=e5733d8c89c3b5 Thank you very much. Also thank you for improving the patch subject. Reinette
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 @@ static void sgx_reclaim_pages(void) 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); } }
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@kernel.org> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com> --- Changes since V2: - V2: https://lore.kernel.org/linux-sgx/be5af586f667c7bcb8ef01286ce75675de5d100f.1642630582.git.reinette.chatre@intel.com/ - Add Reviewed-by from Jarkko. - Remove unused variables. Changes since V1: - V1: https://lore.kernel.org/lkml/ef74bd9548df61f77e802e7505affcfb5159c48c.1642545829.git.reinette.chatre@intel.com/ - Complete rewrite of commit message with significant guidance from Dave who provided the summary as well as troublesome scenario. arch/x86/kernel/cpu/sgx/main.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-)