From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Jarkko Sakkinen" <jarkko@kernel.org>,
"Dmitrii Kuvaiskii" <dmitrii.kuvaiskii@intel.com>,
<dave.hansen@linux.intel.com>, <kai.huang@intel.com>,
<haitao.huang@linux.intel.com>, <reinette.chatre@intel.com>,
<linux-sgx@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: mona.vij@intel.com, kailun.qin@intel.com, stable@vger.kernel.org,
"Marcelina Kościelnicka" <mwk@invisiblethingslab.com>
Subject: Re: [PATCH v2 1/2] x86/sgx: Resolve EAUG race where losing thread returns SIGBUS
Date: Wed, 15 May 2024 16:56:30 +0300 [thread overview]
Message-ID: <D1A9QP6G0PW4.2HI60Q8GUT5YE@kernel.org> (raw)
In-Reply-To: <D1A9PC6LWL2S.38KB2X3EL9X79@kernel.org>
On Wed May 15, 2024 at 4:54 PM EEST, Jarkko Sakkinen wrote:
> On Wed May 15, 2024 at 4:12 PM EEST, Dmitrii Kuvaiskii wrote:
> > diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> > index 279148e72459..41f14b1a3025 100644
> > --- a/arch/x86/kernel/cpu/sgx/encl.c
> > +++ b/arch/x86/kernel/cpu/sgx/encl.c
> > @@ -382,8 +382,11 @@ static vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> > * If ret == -EBUSY then page was created in another flow while
> > * running without encl->lock
> > */
> > - if (ret)
> > + if (ret) {
> > + if (ret == -EBUSY)
> > + vmret = VM_FAULT_NOPAGE;
> > goto err_out_shrink;
> > + }
>
> I agree that there is a bug but it does not categorize as race
> condition.
>
> The bug is simply that for a valid page SIGBUS might be returned.
> The fix is correct but the claim is not.
>
> >
> > pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page);
> > pginfo.addr = encl_page->desc & PAGE_MASK;
> > @@ -419,7 +422,7 @@ static vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> > err_out_shrink:
> > sgx_encl_shrink(encl, va_page);
> > err_out_epc:
> > - sgx_encl_free_epc_page(epc_page);
> > + sgx_free_epc_page(epc_page);
> > err_out_unlock:
> > mutex_unlock(&encl->lock);
> > kfree(encl_page);
>
> Agree with code change 100% but not with the description.
>
> I'd cut out 90% of the description out and just make the argument of
> the wrong error code, and done. The sequence is great for showing
> how this could happen. The prose makes my head hurt tbh.
Also please remember that stable maintainers need to read all of that
if this is a bug fix (it is a bug fix!) :-) So shorted possible legit
argument, no prose and the sequence was awesome :-)
BR, Jarkko
next prev parent reply other threads:[~2024-05-15 13:56 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-15 13:12 [PATCH v2 0/2] x86/sgx: Fix two data races in EAUG/EREMOVE flows Dmitrii Kuvaiskii
2024-05-15 13:12 ` [PATCH v2 1/2] x86/sgx: Resolve EAUG race where losing thread returns SIGBUS Dmitrii Kuvaiskii
2024-05-15 13:54 ` Jarkko Sakkinen
2024-05-15 13:56 ` Jarkko Sakkinen [this message]
2024-05-15 14:15 ` Dave Hansen
2024-05-15 14:28 ` Jarkko Sakkinen
2024-05-15 15:58 ` Reinette Chatre
2024-05-15 16:39 ` Jarkko Sakkinen
2024-05-15 22:01 ` Haitao Huang
2024-05-15 13:12 ` [PATCH v2 2/2] x86/sgx: Resolve EREMOVE page vs EAUG page data race Dmitrii Kuvaiskii
2024-05-15 14:44 ` Jarkko Sakkinen
2024-05-15 15:52 ` Reinette Chatre
2024-05-15 21:59 ` Haitao Huang
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