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SubjectRe: [PATCH v2 2/6] x86/sgx: Do not consider unsanitized pages an error
On Fri, Sep 02, 2022 at 02:57:01AM +0300, Jarkko Sakkinen wrote:
> > Understood that the goal is to only print the
> > number of unsanitized pages if ksgxd has not been
> > stopped prematurely.
>
> Yeah, and thus give as useful information for sysadmin/developer
> as we can.

I figured out how to get best of both worlds. See the
attached patch. I'll send formal series later on.

Keeps the accurancy, just postpones the exit.

BR, Jarkko
From 31c43c3276667cef0a7f0687d489552f26da877b Mon Sep 17 00:00:00 2001
From: Jarkko Sakkinen <jarkko@kernel.org>
Date: Thu, 25 Aug 2022 08:12:30 +0300
Subject: [PATCH] x86/sgx: Do not consider unsanitized pages an error

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 some unsanitized pages, which does
not matter, because SGX will be disabled for the whole power cycle.

This triggers WARN_ON() because sgx_dirty_page_list ends up being
non-empty, and dumps the call stack:

[ 0.268103] sgx: EPC section 0x40200000-0x45f7ffff
[ 0.268591] ------------[ cut here ]------------
[ 0.268592] WARNING: CPU: 6 PID: 83 at
arch/x86/kernel/cpu/sgx/main.c:401 ksgxd+0x1b7/0x1d0
[ 0.268598] Modules linked in:
[ 0.268600] CPU: 6 PID: 83 Comm: ksgxd Not tainted 6.0.0-rc2 #382
[ 0.268603] Hardware name: Dell Inc. XPS 13 9370/0RMYH9, BIOS 1.21.0
07/06/2022
[ 0.268604] RIP: 0010:ksgxd+0x1b7/0x1d0
[ 0.268607] Code: ff e9 f2 fe ff ff 48 89 df e8 75 07 0e 00 84 c0 0f
84 c3 fe ff ff 31 ff e8 e6 07 0e 00 84 c0 0f 85 94 fe ff ff e9 af fe ff
ff <0f> 0b e9 7f fe ff ff e8 dd 9c 95 00 66 66 2e 0f 1f 84 00 00 00 00
[ 0.268608] RSP: 0000:ffffb6c7404f3ed8 EFLAGS: 00010287
[ 0.268610] RAX: ffffb6c740431a10 RBX: ffff8dcd8117b400 RCX:
0000000000000000
[ 0.268612] RDX: 0000000080000000 RSI: ffffb6c7404319d0 RDI:
00000000ffffffff
[ 0.268613] RBP: ffff8dcd820a4d80 R08: ffff8dcd820a4180 R09:
ffff8dcd820a4180
[ 0.268614] R10: 0000000000000000 R11: 0000000000000006 R12:
ffffb6c74006bce0
[ 0.268615] R13: ffff8dcd80e63880 R14: ffffffffa8a60f10 R15:
0000000000000000
[ 0.268616] FS: 0000000000000000(0000) GS:ffff8dcf25580000(0000)
knlGS:0000000000000000
[ 0.268617] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.268619] CR2: 0000000000000000 CR3: 0000000213410001 CR4:
00000000003706e0
[ 0.268620] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 0.268621] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[ 0.268622] Call Trace:
[ 0.268624] <TASK>
[ 0.268627] ? _raw_spin_lock_irqsave+0x24/0x60
[ 0.268632] ? _raw_spin_unlock_irqrestore+0x23/0x40
[ 0.268634] ? __kthread_parkme+0x36/0x90
[ 0.268637] kthread+0xe5/0x110
[ 0.268639] ? kthread_complete_and_exit+0x20/0x20
[ 0.268642] ret_from_fork+0x1f/0x30
[ 0.268647] </TASK>
[ 0.268648] ---[ end trace 0000000000000000 ]---

Ultimately this can crash the kernel, if the following is set:

/proc/sys/kernel/panic_on_warn

In premature stop, print nothing, as the number is by practical means a
random number. Otherwise, it is an indicator of a bug in the driver, and
therefore print the number of unsanitized pages with pr_err().

Link: https://lore.kernel.org/linux-sgx/20220825051827.246698-1-jarkko@kernel.org/T/#u
Fixes: 51ab30eb2ad4 ("x86/sgx: Replace section->init_laundry_list with sgx_dirty_page_list")
Cc: stable@vger.kernel.org # v5.13+
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

v6:
- Address Reinette's feedback:
https://lore.kernel.org/linux-sgx/Yw6%2FiTzSdSw%2FY%2FVO@kernel.org/

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..f29dcaddd140 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)
{
struct sgx_epc_page *page;
+ long 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;
+ 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);

- /* 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 (ret)
+ pr_err("%ld unsanitized pages\n", left_dirty);

while (!kthread_should_stop()) {
if (try_to_freeze())
--
2.37.2
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