linux-kernel - Re: [PATCH v4] x86/sgx: Do not consider unsanitized pages an error

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Message-ID: <fd6f124d-1d7d-0e73-10bd-f7aaae45ee68@molgen.mpg.de>
Date:   Fri, 26 Aug 2022 14:51:15 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-sgx@...r.kernel.org
Cc:     Haitao Huang <haitao.huang@...ux.intel.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] x86/sgx: Do not consider unsanitized pages an error

Dear Jarkko,


Thank you for the patch.

Am 26.08.22 um 03:41 schrieb Jarkko Sakkinen:
> In sgx_init(), if misc_register() for the provision device fails, and
> neither sgx_drv_init() nor sgx_vepc_init() succeeds, then ksgxd will be
> prematurely stopped.
> 
> This triggers WARN_ON() because sgx_dirty_page_list ends up being
> non-empty. Ultimately this can crash the kernel, depending on the kernel
> command line, which is not correct behavior because SGX driver is not
> working incorrectly.

Maybe paste the WARN_ON trace, so `git log` can be searched for the 
trace too.

> Print simple warning instead, and improve the output by printing the
> number of unsanitized pages.

See below, but no warning seems to be logged in my case now. (I should 
test Linus’ current master too.)

> Link: https://lore.kernel.org/linux-sgx/20220825051827.246698-1-jarkko@kernel.org/T/#u
> Reported-by: Paul Menzel <pmenzel@...gen.mpg.de>
> Fixes: 51ab30eb2ad4 ("x86/sgx: Replace section->init_laundry_list with sgx_dirty_page_list")
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
> Cc: Haitao Huang <haitao.huang@...ux.intel.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Reinette Chatre <reinette.chatre@...el.com>
> 
> 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 | 19 +++++++++++++------
>   1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 515e2a5f25bb..903100fcfce3 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -49,17 +49,20 @@ 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.
>    */
> -static void __sgx_sanitize_pages(struct list_head *dirty_page_list)
> +static int __sgx_sanitize_pages(struct list_head *dirty_page_list)
>   {
>   	struct sgx_epc_page *page;
> +	int left_dirty = 0;
>   	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;
> +			break;
>   
>   		page = list_first_entry(dirty_page_list, struct sgx_epc_page, list);
>   
> @@ -92,12 +95,14 @@ 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)
> @@ -388,6 +393,8 @@ void sgx_reclaim_direct(void)
>   
>   static int ksgxd(void *p)
>   {
> +	int left_dirty;
> +
>   	set_freezable();
>   
>   	/*
> @@ -395,10 +402,10 @@ static int ksgxd(void *p)
>   	 * required for SECS pages, whose child pages blocked EREMOVE.
>   	 */
>   	__sgx_sanitize_pages(&sgx_dirty_page_list);
> -	__sgx_sanitize_pages(&sgx_dirty_page_list);
>   
> -	/* sanity check: */
> -	WARN_ON(!list_empty(&sgx_dirty_page_list));
> +	left_dirty = __sgx_sanitize_pages(&sgx_dirty_page_list);
> +	if (left_dirty)
> +		pr_warn("%d unsanitized pages\n", left_dirty);
>   
>   	while (!kthread_should_stop()) {
>   		if (try_to_freeze())

I tested this on top of commit 4c612826bec1 (Merge tag 'net-6.0-rc3' of 
git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net) and the 
warning trace is gone.

     [    0.255192] calling  sgx_init+0x0/0x409 @ 1
     [    0.255207] sgx: EPC section 0x40200000-0x45f7ffff
     [    0.255747] initcall sgx_init+0x0/0x409 returned -19 after 552 usecs

(OT: If -19 suggests something failed, a message, why sgx_init() failed 
would be nice.)

Please find the whole output of `dmesg` attached.


Kind regards,

Paul
View attachment "20220826--linux-6.0-rc2--dmesg.txt" of type "text/plain" (192145 bytes)