From: Jarkko Sakkinen <jarkko@kernel.org>
To: Jakob Koschel <jkl820.git@gmail.com>
Cc: 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>,
linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org,
Pietro Borrello <borrello@diag.uniroma1.it>,
Cristiano Giuffrida <c.giuffrida@vu.nl>,
"Bos, H.J." <h.j.bos@vu.nl>
Subject: Re: [PATCH v2] x86/sgx: Avoid using iterator after loop in sgx_mmu_notifier_release()
Date: Thu, 2 Mar 2023 01:07:24 +0200 [thread overview]
Message-ID: <Y//arJZXs4JtqnHt@kernel.org> (raw)
In-Reply-To: <20230206-sgx-use-after-iter-v2-1-736ca621adc3@gmail.com>
On Wed, Mar 01, 2023 at 12:17:29PM +0100, Jakob Koschel wrote:
> If &encl_mm->encl->mm_list does not contain the searched 'encl_mm',
> 'tmp' will not point to a valid sgx_encl_mm struct.
>
> Linus proposed to avoid any use of the list iterator variable after the
> loop, in the attempt to move the list iterator variable declaration into
> the marcro to avoid any potential misuse after the loop.
> Using it in a pointer comparision after the loop is undefined behavior
> and should be omitted if possible [1].
>
> Instead we'll just use a 'found' boolean to indicate if an element
> was found.
>
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jkl820.git@gmail.com>
> ---
> Changes in v2:
> - refactor to use 'found' variable instead of moving code into the loop
> - add cover letter info into the patch
> - Link to v1: https://lore.kernel.org/r/20230206-sgx-use-after-iter-v1-1-c09fb5300b5e@gmail.com
> ---
> arch/x86/kernel/cpu/sgx/encl.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 2a0e90fe2abc..91fa70e51004 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -755,6 +755,7 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn,
> {
> struct sgx_encl_mm *encl_mm = container_of(mn, struct sgx_encl_mm, mmu_notifier);
> struct sgx_encl_mm *tmp = NULL;
> + bool found = false;
>
> /*
> * The enclave itself can remove encl_mm. Note, objects can't be moved
> @@ -764,12 +765,13 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn,
> list_for_each_entry(tmp, &encl_mm->encl->mm_list, list) {
> if (tmp == encl_mm) {
> list_del_rcu(&encl_mm->list);
> + found = true;
> break;
> }
> }
> spin_unlock(&encl_mm->encl->mm_lock);
>
> - if (tmp == encl_mm) {
> + if (found) {
> synchronize_srcu(&encl_mm->encl->srcu);
> mmu_notifier_put(mn);
> }
>
> ---
> base-commit: d2d11f342b179f1894a901f143ec7c008caba43e
> change-id: 20230206-sgx-use-after-iter-f584c1d64c87
>
> Best regards,
> --
> Jakob Koschel <jkl820.git@gmail.com>
>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
BR, Jarkko
prev parent reply other threads:[~2023-03-01 23:07 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-01 11:17 [PATCH v2] x86/sgx: Avoid using iterator after loop in sgx_mmu_notifier_release() Jakob Koschel
2023-03-01 23:07 ` Jarkko Sakkinen [this message]
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