From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
linux-sgx@vger.kernel.org, akpm@linux-foundation.org,
dave.hansen@intel.com, nhorman@redhat.com, npmccallum@redhat.com,
haitao.huang@intel.com, andriy.shevchenko@linux.intel.com,
tglx@linutronix.de, kai.svahn@intel.com, bp@alien8.de,
josh@joshtriplett.org, luto@kernel.org, kai.huang@intel.com,
rientjes@google.com, cedric.xing@intel.com,
puiterwijk@redhat.com, linux-mm@kvack.org,
Jethro Beekman <jethro@fortanix.com>,
Jordan Hand <jorhand@linux.microsoft.com>,
Chunyang Hui <sanqian.hcy@antfin.com>,
Seth Moore <sethmo@google.com>
Subject: Re: [PATCH v30 12/20] x86/sgx: Add a page reclaimer
Date: Thu, 21 May 2020 23:58:02 -0700 [thread overview]
Message-ID: <20200522065802.GC23459@linux.intel.com> (raw)
In-Reply-To: <20200515004410.723949-13-jarkko.sakkinen@linux.intel.com>
On Fri, May 15, 2020 at 03:44:02AM +0300, Jarkko Sakkinen wrote:
> +/**
> + * sgx_reclaim_pages() - Reclaim EPC pages from the consumers
> + *
> + * Take a fixed number of pages from the head of the active page pool and
> + * reclaim them to the enclave's private shmem files. Skip the pages, which
> + * have been accessed since the last scan. Move those pages to the tail of
> + * active page pool so that the pages get scanned in LRU like fashion.
> + */
> +void sgx_reclaim_pages(void)
> +{
> + struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
> + struct sgx_backing backing[SGX_NR_TO_SCAN];
> + struct sgx_epc_section *section;
> + struct sgx_encl_page *encl_page;
> + struct sgx_epc_page *epc_page;
> + int cnt = 0;
> + int ret;
> + int i;
> +
> + spin_lock(&sgx_active_page_list_lock);
> + for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> + if (list_empty(&sgx_active_page_list))
> + break;
> +
> + epc_page = list_first_entry(&sgx_active_page_list,
> + struct sgx_epc_page, list);
> + list_del_init(&epc_page->list);
> + encl_page = epc_page->owner;
> +
> + if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
> + chunk[cnt++] = epc_page;
> + else
> + /* The owner is freeing the page. No need to add the
> + * page back to the list of reclaimable pages.
> + */
> + epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> + }
> + spin_unlock(&sgx_active_page_list_lock);
> +
> + for (i = 0; i < cnt; i++) {
> + epc_page = chunk[i];
> + encl_page = epc_page->owner;
> +
> + if (!sgx_reclaimer_age(epc_page))
> + goto skip;
> +
> + ret = sgx_encl_get_backing(encl_page->encl,
> + SGX_ENCL_PAGE_INDEX(encl_page),
> + &backing[i]);
> + if (ret)
> + goto skip;
> +
> + mutex_lock(&encl_page->encl->lock);
> + encl_page->desc |= SGX_ENCL_PAGE_RECLAIMED;
> + mutex_unlock(&encl_page->encl->lock);
> + continue;
> +
> +skip:
> + kref_put(&encl_page->encl->refcount, sgx_encl_release);
> +
> + spin_lock(&sgx_active_page_list_lock);
> + list_add_tail(&epc_page->list, &sgx_active_page_list);
> + spin_unlock(&sgx_active_page_list_lock);
Ugh, this is wrong. If the above kref_put() drops the last reference and
releases the enclave, adding the page to the active page list will result
in a use-after-free as the enclave will have been freed. It also leaks the
EPC page because sgx_encl_destroy() skips pages that are in the process of
being reclaimed (as detected by list_empty()).
The "original" code did the put() after list_add_tail(), but was moved in
v15 to fix a bug where the put() could drop a reference to the wrong enclave
if the page was freed and reallocated by a different CPU between
list_add_tail() and put(). But, that particular bug only occurred because
the code at the time was:
sgx_encl_page_put(epc_page);
I.e. the backpointer in epc_page was consumed after dropping the spin lock.
So long as epc_page->owner (well, epc_page in general) isn't dereferenced,
I'm 99% certain this can be fixed simply by doing kref_put() after moving
the page back to the active page list.
> +
> + chunk[i] = NULL;
> + }
> +
> + for (i = 0; i < cnt; i++) {
> + epc_page = chunk[i];
> + if (epc_page)
> + sgx_reclaimer_block(epc_page);
> + }
> +
> + for (i = 0; i < cnt; i++) {
> + epc_page = chunk[i];
> + if (!epc_page)
> + continue;
> +
> + encl_page = epc_page->owner;
> + sgx_reclaimer_write(epc_page, &backing[i]);
> + sgx_encl_put_backing(&backing[i], true);
> +
> + kref_put(&encl_page->encl->refcount, sgx_encl_release);
> + epc_page->desc &= ~SGX_EPC_PAGE_RECLAIMABLE;
> +
> + section = sgx_epc_section(epc_page);
> + spin_lock(§ion->lock);
> + list_add_tail(&epc_page->list, §ion->page_list);
> + section->free_cnt++;
> + spin_unlock(§ion->lock);
> + }
> +}
next prev parent reply other threads:[~2020-05-22 6:58 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-15 0:43 [PATCH v30 00/20] Intel SGX foundations Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 01/20] x86/cpufeatures: x86/msr: Add Intel SGX hardware bits Jarkko Sakkinen
2020-05-20 12:16 ` Borislav Petkov
2020-05-20 14:00 ` Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 02/20] x86/cpufeatures: x86/msr: Intel SGX Launch Control " Jarkko Sakkinen
2020-05-20 12:23 ` Borislav Petkov
2020-05-20 14:04 ` Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 03/20] x86/mm: x86/sgx: Signal SIGSEGV with PF_SGX Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 04/20] x86/sgx: Add SGX microarchitectural data structures Jarkko Sakkinen
2020-05-20 18:47 ` Borislav Petkov
2020-05-20 21:04 ` Sean Christopherson
2020-05-22 15:54 ` Jarkko Sakkinen
2020-05-22 16:13 ` Sean Christopherson
2020-05-22 19:50 ` Jarkko Sakkinen
2020-05-25 8:20 ` Borislav Petkov
2020-05-27 19:43 ` Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 05/20] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 06/20] x86/cpu/intel: Detect SGX support Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 07/20] x86/sgx: Enumerate and track EPC sections Jarkko Sakkinen
2020-05-25 9:23 ` Borislav Petkov
2020-05-27 3:56 ` Sean Christopherson
2020-05-27 20:35 ` Borislav Petkov
2020-05-28 7:36 ` Jarkko Sakkinen
2020-05-28 5:25 ` Jarkko Sakkinen
2020-05-28 5:35 ` Jarkko Sakkinen
2020-05-28 6:14 ` Jarkko Sakkinen
2020-05-28 6:16 ` Jarkko Sakkinen
2020-05-28 5:13 ` Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 08/20] x86/sgx: Add functions to allocate and free EPC pages Jarkko Sakkinen
2020-05-26 12:52 ` Borislav Petkov
2020-05-27 4:21 ` Sean Christopherson
2020-05-27 20:46 ` Borislav Petkov
2020-05-28 0:52 ` Sean Christopherson
2020-05-28 6:51 ` Jarkko Sakkinen
2020-05-28 1:23 ` Jarkko Sakkinen
2020-05-28 1:36 ` Sean Christopherson
2020-05-28 6:52 ` Jarkko Sakkinen
2020-05-28 17:16 ` Borislav Petkov
2020-05-28 17:19 ` Sean Christopherson
2020-05-28 17:27 ` Borislav Petkov
2020-05-28 17:34 ` Sean Christopherson
2020-05-28 19:07 ` Jarkko Sakkinen
2020-05-28 19:59 ` Sean Christopherson
2020-05-29 3:28 ` Jarkko Sakkinen
2020-05-29 3:37 ` Sean Christopherson
2020-05-29 5:07 ` Jarkko Sakkinen
2020-05-29 8:12 ` Jarkko Sakkinen
2020-05-29 8:13 ` Jarkko Sakkinen
2020-05-29 3:38 ` Jarkko Sakkinen
2020-05-15 0:43 ` [PATCH v30 09/20] mm: Introduce vm_ops->may_mprotect() Jarkko Sakkinen
2020-05-29 12:10 ` Borislav Petkov
2020-05-29 18:18 ` Jarkko Sakkinen
2020-05-29 18:28 ` Dave Hansen
2020-05-31 23:12 ` Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 10/20] x86/sgx: Linux Enclave Driver Jarkko Sakkinen
2020-05-21 19:12 ` Sean Christopherson
2020-05-22 19:26 ` Jarkko Sakkinen
2020-05-22 19:39 ` Jarkko Sakkinen
2020-05-22 3:33 ` Sean Christopherson
2020-05-15 0:44 ` [PATCH v30 11/20] x86/sgx: Add provisioning Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 12/20] x86/sgx: Add a page reclaimer Jarkko Sakkinen
2020-05-22 6:58 ` Sean Christopherson [this message]
2020-05-22 19:57 ` Jarkko Sakkinen
2020-05-22 21:52 ` Sean Christopherson
2020-05-22 7:15 ` Sean Christopherson
2020-05-22 19:47 ` Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 13/20] x86/sgx: ptrace() support for the SGX driver Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 14/20] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 15/20] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 16/20] x86/traps: Attempt to fixup exceptions in vDSO before signaling Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 17/20] x86/vdso: Implement a vDSO for Intel SGX enclave call Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 18/20] selftests/x86: Add a selftest for SGX Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 19/20] docs: x86/sgx: Document SGX micro architecture and kernel internals Jarkko Sakkinen
2020-05-15 0:44 ` [PATCH v30 20/20] x86/sgx: Update MAINTAINERS Jarkko Sakkinen
2020-05-16 8:57 ` [PATCH] x86/cpu/intel: Add nosgx kernel parameter Jarkko Sakkinen
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