On Sat, Sep 03, 2022 at 09:01:07AM +0300, Jarkko Sakkinen wrote: > Unsanitized pages trigger WARN_ON() unconditionally, which can panic the > whole computer, if /proc/sys/kernel/panic_on_warn is set. > > In sgx_init(), if misc_register() fails or misc_register() succeeds but > neither sgx_drv_init() nor sgx_vepc_init() succeeds, then ksgxd will be > prematurely stopped. This may leave unsanitized pages, which will result a > false warning. > > Refine __sgx_sanitize_pages() to return: > > 1. Zero when the sanitization process is complete or ksgxd has been > requested to stop. > 2. The number of unsanitized pages otherwise. > > Use the return value as the criteria for triggering output, and tone down > the output to pr_err() to prevent the whole system to be taken down if for > some reason sanitization process does not complete. > > Link: https://lore.kernel.org/linux-sgx/20220825051827.246698-1-jarkko@xxxxxxxxxx/T/#u > Fixes: 51ab30eb2ad4 ("x86/sgx: Replace section->init_laundry_list with sgx_dirty_page_list") > Cc: stable@xxxxxxxxxxxxxxx # v5.13+ > Reported-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx> > Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > --- > v7: > - Rewrote commit message. > - Do not return -ECANCELED on premature stop. Instead use zero both > premature stop and complete sanitization. > > v6: > - Address Reinette's feedback: > https://lore.kernel.org/linux-sgx/Yw6%2FiTzSdSw%2FY%2FVO@xxxxxxxxxx/ > > v5: > - Add the klog dump and sysctl option to the commit message. > > v4: > - Explain expectations for dirty_page_list in the function header, instead > of an inline comment. > - Improve commit message to explain the conditions better. > - Return the number of pages left dirty to ksgxd() and print warning after > the 2nd call, if there are any. > > v3: > - Remove WARN_ON(). > - Tuned comments and the commit message a bit. > > v2: > - Replaced WARN_ON() with optional pr_info() inside > __sgx_sanitize_pages(). > - Rewrote the commit message. > - Added the fixes tag. > --- > arch/x86/kernel/cpu/sgx/main.c | 33 ++++++++++++++++++++++++++------- > 1 file changed, 26 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c > index 515e2a5f25bb..c0a5ce19c608 100644 > --- a/arch/x86/kernel/cpu/sgx/main.c > +++ b/arch/x86/kernel/cpu/sgx/main.c > @@ -49,17 +49,23 @@ static LIST_HEAD(sgx_dirty_page_list); > * Reset post-kexec EPC pages to the uninitialized state. The pages are removed > * from the input list, and made available for the page allocator. SECS pages > * prepending their children in the input list are left intact. > + * > + * Contents of the @dirty_page_list must be thread-local, i.e. > + * not shared by multiple threads. > + * > + * Return 0 when sanitization was successful or kthread was stopped, and the > + * number of unsanitized pages otherwise. > */ > -static void __sgx_sanitize_pages(struct list_head *dirty_page_list) > +static unsigned long __sgx_sanitize_pages(struct list_head *dirty_page_list) > { > + unsigned long left_dirty = 0; > struct sgx_epc_page *page; > LIST_HEAD(dirty); > int ret; > > - /* dirty_page_list is thread-local, no need for a lock: */ > while (!list_empty(dirty_page_list)) { > if (kthread_should_stop()) > - return; > + return 0; > > page = list_first_entry(dirty_page_list, struct sgx_epc_page, list); > > @@ -92,12 +98,14 @@ static void __sgx_sanitize_pages(struct list_head *dirty_page_list) > } else { > /* The page is not yet clean - move to the dirty list. */ > list_move_tail(&page->list, &dirty); > + left_dirty++; > } > > cond_resched(); > } > > list_splice(&dirty, dirty_page_list); > + return left_dirty; > } > > static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page) > @@ -388,17 +396,28 @@ void sgx_reclaim_direct(void) > > static int ksgxd(void *p) > { > + unsigned long left_dirty; > + > set_freezable(); > > /* > * Sanitize pages in order to recover from kexec(). The 2nd pass is > * required for SECS pages, whose child pages blocked EREMOVE. > */ > - __sgx_sanitize_pages(&sgx_dirty_page_list); > - __sgx_sanitize_pages(&sgx_dirty_page_list); > + left_dirty = __sgx_sanitize_pages(&sgx_dirty_page_list); > + pr_debug("%ld unsanitized pages\n", left_dirty); %lu > > - /* sanity check: */ > - WARN_ON(!list_empty(&sgx_dirty_page_list)); > + left_dirty = __sgx_sanitize_pages(&sgx_dirty_page_list); > + /* > + * Never expected to happen in a working driver. If it happens the bug > + * is expected to be in the sanitization process, but successfully > + * sanitized pages are still valid and driver can be used and most > + * importantly debugged without issues. To put short, the global state > + * of kernel is not corrupted so no reason to do any more complicated > + * rollback. > + */ > + if (left_dirty) > + pr_err("%ld unsanitized pages\n", left_dirty); %lu > > while (!kthread_should_stop()) { > if (try_to_freeze()) > -- > 2.37.2 > BR, Jarkko
