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Date:   Fri, 25 Jun 2021 08:47:30 +0800
From:   Du Cheng <ducheng2@gmail.com>
To:     Jarkko Sakkinen <jarkko@kernel.org>
Cc:     Sean Christopherson <seanjc@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-sgx@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/sgx: Suppress WARN on inability to sanitize EPC if
 ksgxd is stopped
Message-ID: <YNUnoqUsU2b1GC2C@nuc>
References: <20210616004458.2192889-1-seanjc@google.com>
 <YMmUHRGwXSIYJTDf@nuc>
 <20210623133219.v6c62zwtj5qowib3@kernel.org>
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Le Wed, Jun 23, 2021 at 04:32:19PM +0300, Jarkko Sakkinen a écrit :
> On Wed, Jun 16, 2021 at 02:03:09PM +0800, Du Cheng wrote:
> > Le Tue, Jun 15, 2021 at 05:44:58PM -0700, Sean Christopherson a écrit :
> > > Don't WARN on having unsanitized EPC pages if ksgxd is stopped early,
> > > e.g. if sgx_init() realizes there will be no downstream consumers of EPC.
> > > If ksgxd is stopped early, EPC pages may be left on the dirty list, but
> > > that's ok because ksgxd is only stopped if SGX initialization failed or
> > > if the kernel is going down.  In either case, the EPC won't be used.
> > > 
> > > This bug was exposed by the addition of KVM support, but has existed and
> > > was hittable since the original sanitization code was added.  Prior to
> > > adding KVM support, if Launch Control was not fully enabled, e.g. when
> > > running on older hardware, sgx_init() bailed immediately before spawning
> > > ksgxd because X86_FEATURE_SGX was cleared if X86_FEATURE_SGX_LC was
> > > unsupported.
> > > 
> > > With KVM support, sgx_drv_init() handles the X86_FEATURE_SGX_LC check
> > > manually, so now there's any easy-to-hit case where sgx_init() will spawn
> > > ksgxd and _then_ fail to initialize, which results in sgx_init() stopping
> > > ksgxd before it finishes sanitizing the EPC.
> > > 
> > > Prior to KVM support, the bug was much harder to hit because it basically
> > > required char device registration to fail.
> > > 
> > > Reported-by: Du Cheng <ducheng2@gmail.com>
> > > Fixes: e7e0545299d8 ("x86/sgx: Initialize metadata for Enclave Page Cache (EPC) sections")
> > > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > > ---
> > > 
> > > Lightly tested due to lack of hardware.  I hacked the flow to verify that
> > > stopping early will leave work pending, and that rechecking should_stop()
> > > suppress the resulting WARN.
> > > 
> > >  arch/x86/kernel/cpu/sgx/main.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> > > index ad904747419e..fbad2b9625a5 100644
> > > --- a/arch/x86/kernel/cpu/sgx/main.c
> > > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > > @@ -425,7 +425,7 @@ static int ksgxd(void *p)
> > >  	__sgx_sanitize_pages(&sgx_dirty_page_list);
> > >  
> > >  	/* sanity check: */
> > > -	WARN_ON(!list_empty(&sgx_dirty_page_list));
> > > +	WARN_ON(!list_empty(&sgx_dirty_page_list) && !kthread_should_stop());
> > >  
> > >  	while (!kthread_should_stop()) {
> > >  		if (try_to_freeze())
> > > -- 
> > > 2.32.0.272.g935e593368-goog
> > > 
> > 
> > I applied this patch on 5.13-rc6, and it no longer causes to trigger WARN_ON()
> > on my NUC:
> > 
> > ```
> > 
> > [    0.669411] PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> > [    0.669412] software IO TLB: mapped [mem 0x0000000017cb9000-0x000000001bcb9000] (64MB)
> > [    0.672788] platform rtc_cmos: registered platform RTC device (no PNP device found)
> > [    0.672805] sgx: EPC section 0x30200000-0x35f7ffff
> > [    0.674239] Initialise system trusted keyrings
> > [    0.674254] Key type blacklist registered
> > 
> > ```
> > 
> > Regards,
> > Du Cheng
> 
> Can you thus give a tested-by for this?
> 
> /Jarkko

Certainly.

Tested-by: Du Cheng <ducheng2@gmail.com>