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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <fb9b4f10-b824-4e3c-d29f-f8bbb030cd96@intel.com>
Date:   Tue, 27 Jun 2023 16:46:00 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Mark Brown <broonie@...nel.org>,
        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 6/27/23 10:20, Mark Brown wrote:
> 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.

Yeah, that looks odd.  Also odd is that none of the other users of
vm_munmap() bother to check the return value (except for one passthrough
in the nommu code).

I don't think the EINTR happens during contention, though.  It's really
there to be able break out in the face of SIGKILL.  I think that's why
nobody handles it: the task is dying anyway and nobody cares.

Rick, was this hunk here for a specific reason or were you just trying
to be diligent in handling errors?