From: Jarkko Sakkinen <jarkko@kernel.org>
To: linux-sgx@vger.kernel.org
Cc: dave.hansen@intel.com, Jarkko Sakkinen <jarkko@kernel.org>,
Haitao Huang <haitao.huang@linux.intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Sean Christopherson <seanjc@google.com>,
Jethro Beekman <jethro@fortanix.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH v8] x86/sgx: Maintain encl->refcount for each encl->mm_list entry
Date: Mon, 8 Feb 2021 00:14:01 +0200 [thread overview]
Message-ID: <20210207221401.29933-1-jarkko@kernel.org> (raw)
This has been shown in tests:
[ +0.000008] WARNING: CPU: 3 PID: 7620 at kernel/rcu/srcutree.c:374 cleanup_srcu_struct+0xed/0x100
This is essentially a use-after free, although SRCU notices it as
an SRCU cleanup in an invalid context.
== Background ==
SGX has a data structure (struct sgx_encl_mm) which keeps per-mm SGX
metadata. This is separate from 'struct sgx_encl' because, in theory,
an enclave can be mapped from more than one mm. sgx_encl_mm includes
a pointer back to the sgx_encl.
This means that sgx_encl must have a longer lifetime than all of the
sgx_encl_mm's that point to it. That's usually the case: sgx_encl_mm
is freed only after the mmu_notifier is unregistered in sgx_release().
However, there's a race. If the process is exiting,
sgx_mmu_notifier_release() can be called in parallel with sgx_release()
instead of being called *by* it. The mmu_notifier path keeps encl_mm
alive past when sgx_encl can be freed. This inverts the lifetime rules
and means that sgx_mmu_notifier_release() can access a freed sgx_encl.
== Fix ==
Increase encl->refcount when encl_mm->encl is established. Release
this reference encl_mm is freed. This ensures that 'encl' outlives
'encl_mm'.
Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
Cc: Dave Hansen <dave.hansen@linux.intel.com
Reported-by: Haitao Huang <haitao.huang@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v8:
- Slight adjustments on call sites suggested by Dave, to make things
more clear and obvious. Otherwise, semantically same as v7:
https://lore.kernel.org/linux-sgx/b874673d-9d58-0d6f-ce2d-ef4d33ac5115@intel.com/
Contains also long description written by Dave.
v7:
- No changes from v6. Resend of
https://patchwork.kernel.org/project/intel-sgx/patch/20210204143845.39697-1-jarkko@kernel.org/
v6:
- Maintain refcount for each encl->mm_list entry.
v5:
- To make sure that the instance does not get deleted use kref_get()
kref_put(). This also removes the need for additional
synchronize_srcu().
v4:
- Rewrite the commit message.
- Just change the call order. *_expedited() is out of scope for this
bug fix.
v3: Fine-tuned tags, and added missing change log for v2.
v2: Switch to synchronize_srcu_expedited().
arch/x86/kernel/cpu/sgx/driver.c | 3 +++
arch/x86/kernel/cpu/sgx/encl.c | 5 +++++
2 files changed, 8 insertions(+)
diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index f2eac41bb4ff..8ce6d8371cfb 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -72,6 +72,9 @@ static int sgx_release(struct inode *inode, struct file *file)
synchronize_srcu(&encl->srcu);
mmu_notifier_unregister(&encl_mm->mmu_notifier, encl_mm->mm);
kfree(encl_mm);
+
+ /* 'encl_mm' is gone, put encl_mm->encl reference: */
+ kref_put(&encl->refcount, sgx_encl_release);
}
kref_put(&encl->refcount, sgx_encl_release);
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 20a2dd5ba2b4..7449ef33f081 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -473,6 +473,9 @@ static void sgx_mmu_notifier_free(struct mmu_notifier *mn)
{
struct sgx_encl_mm *encl_mm = container_of(mn, struct sgx_encl_mm, mmu_notifier);
+ /* 'encl_mm' is going away, put encl_mm->encl reference: */
+ kref_put(&encl_mm->encl->refcount, sgx_encl_release);
+
kfree(encl_mm);
}
@@ -526,6 +529,8 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm)
if (!encl_mm)
return -ENOMEM;
+ /* Grab a refcount for the encl_mm->encl reference: */
+ kref_get(&encl->refcount);
encl_mm->encl = encl;
encl_mm->mm = mm;
encl_mm->mmu_notifier.ops = &sgx_mmu_notifier_ops;
--
2.30.0
next reply other threads:[~2021-02-07 22:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-07 22:14 Jarkko Sakkinen [this message]
2021-02-07 22:37 ` [PATCH v8] x86/sgx: Maintain encl->refcount for each encl->mm_list entry Dave Hansen
2021-04-14 1:15 ` Haitao Huang
2021-04-14 15:51 ` Sean Christopherson
2021-04-14 16:58 ` Dave Hansen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210207221401.29933-1-jarkko@kernel.org \
--to=jarkko@kernel.org \
--cc=bp@alien8.de \
--cc=dave.hansen@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=haitao.huang@linux.intel.com \
--cc=hpa@zytor.com \
--cc=jethro@fortanix.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-sgx@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).