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    SubjectRe: [PATCH v4] x86/sgx: Do not consider unsanitized pages an error
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    Dear Jarkko,


    Am 26.08.22 um 14:51 schrieb Paul Menzel:

    […]

    > 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.)

    Just for the record, the problem still exists in Linus’ master branch:

    ```
    [ 0.000000] Linux version 6.0.0-rc2 (root@4beb429beb4a) (gcc (Debian
    11.3.0-3) 11.3.0, GNU ld (GNU Binutils for Debian) 2.38) #382 SMP
    PREEMPT_DYNAMIC Fri Aug 26 12:52:15 UTC 2022
    [ 0.000000] Command line: BOOT_IMAGE=/vmlinuz-6.0.0-rc2
    root=UUID=56f398e0-1e25-4fda-aa9f-611dece4b333 ro quiet
    module_blacklist=psmouse initcall_debug log_buf_len=4M cryptomgr.notests
    […]
    [ 0.268089] calling sgx_init+0x0/0x409 @ 1
    [ 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 ]---
    [ 0.268694] initcall sgx_init+0x0/0x409 returned -19 after 603 usecs
    ```

    Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>

    >> Link: https://lore.kernel.org/linux-sgx/20220825051827.246698-1-jarkko@kernel.org/T/#u
    >> Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
    >> Fixes: 51ab30eb2ad4 ("x86/sgx: Replace section->init_laundry_list with sgx_dirty_page_list")
    >> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
    >> ---
    >> Cc: Haitao Huang <haitao.huang@linux.intel.com>
    >> Cc: Dave Hansen <dave.hansen@linux.intel.com>
    >> Cc: Reinette Chatre <reinette.chatre@intel.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

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