linux-kernel - Re: [PATCH v9 28/42] x86/shstk: Add user-mode shadow stack support

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Message-ID: <76a87cdf-4d4f-4b3f-b01f-0540eab71ac7@sirena.org.uk>
Date:   Tue, 27 Jun 2023 18:20:21 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        david@...hat.com, debug@...osinc.com, szabolcs.nagy@....com,
        torvalds@...ux-foundation.org, Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v9 28/42] x86/shstk: Add user-mode shadow stack support

On Mon, Jun 12, 2023 at 05:10:54PM -0700, Rick Edgecombe wrote:

> +static void unmap_shadow_stack(u64 base, u64 size)
> +{
> +	while (1) {
> +		int r;
> +
> +		r = vm_munmap(base, size);
> +
> +		/*
> +		 * vm_munmap() returns -EINTR when mmap_lock is held by
> +		 * something else, and that lock should not be held for a
> +		 * long time.  Retry it for the case.
> +		 */
> +		if (r == -EINTR) {
> +			cond_resched();
> +			continue;
> +		}

This looks generic, not even shadow stack specific - was there any
discussion of making it a vm_munmap_retry() (that's not a great name...)
or similar?  I didn't see any in old versions of the thread but I
might've missed something.

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