From: "Haitao Huang" <haitao.huang@linux.intel.com>
To: linux-sgx@vger.kernel.org, "Jarkko Sakkinen" <jarkko@kernel.org>
Cc: dave.hansen@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: Re: [PATCH v8] x86/sgx: Maintain encl->refcount for each encl->mm_list entry
Date: Tue, 13 Apr 2021 20:15:09 -0500 [thread overview]
Message-ID: <op.01te3jzwwjvjmi@mqcpg7oapc828.gar.corp.intel.com> (raw)
In-Reply-To: <20210207221401.29933-1-jarkko@kernel.org>
On Sun, 07 Feb 2021 16:14:01 -0600, Jarkko Sakkinen <jarkko@kernel.org>
wrote:
> 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.
>
The comments in code around this warning indicate a potential memory leak.
Not sure how use-after-free come into play. Anyway, this fix seems to work
for the warning above.
However, I still have doubts on another potential race. See below.
> 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);
Note here you are freeing the encl_mm, outside protection of
encl->refcount.
> +
> + /* '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);
Could this access to and kfree of encl_mm possibly be after the
kfree(encl_mm) noted above?
Also is there a reason we do kfree(encl_mm) in notifier_free not directly
in notifier_release?
Thanks
Haitao
next prev parent reply other threads:[~2021-04-14 1:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-07 22:14 [PATCH v8] x86/sgx: Maintain encl->refcount for each encl->mm_list entry Jarkko Sakkinen
2021-02-07 22:37 ` Dave Hansen
2021-04-14 1:15 ` Haitao Huang [this message]
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=op.01te3jzwwjvjmi@mqcpg7oapc828.gar.corp.intel.com \
--to=haitao.huang@linux.intel.com \
--cc=bp@alien8.de \
--cc=dave.hansen@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=jarkko@kernel.org \
--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).