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Date: Wed, 26 Jun 2019 19:04:12 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Andy Lutomirski <luto@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Linux API <linux-api@...r.kernel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-x86_64@...r.kernel.org, linux-arch <linux-arch@...r.kernel.org>, Kees Cook <keescook@...omium.org>, "Carlos O'Donell" <carlos@...hat.com>, X86 ML <x86@...nel.org>
Subject: Re: Detecting the availability of VSYSCALL
* Andy Lutomirski:
> On Wed, Jun 26, 2019 at 9:45 AM Florian Weimer <fweimer@...hat.com> wrote:
>>
>> * Andy Lutomirski:
>>
>> > Can’t an ELF note be done with some more or less ordinary asm such
>> > that any link editor will insert it correctly?
>>
>> We've just been over this for the CET enablement. ELF PT_NOTE parsing
>> was rejected there.
>
> No one told me this. Unless I missed something, the latest kernel
> patches still had PT_NOTE parsing. Can you point me at an
> enlightening thread or explain what happened?
The ABI was changed rather late, and PT_GNU_PROPERTY has been added.
But this is okay because the kernel only looks at the dynamic loader,
which we can update fairly easily.
The thread is:
Subject: Re: [PATCH v7 22/27] binfmt_elf: Extract .note.gnu.property from an ELF file
<87blyu7ubf.fsf@...enburg2.str.redhat.com> is a message reference in it.
>> > The problem with a personality flag is that it needs to have some kind
>> > of sensible behavior for setuid programs, and getting that right in a
>> > way that doesn’t scream “exploit me” while preserving useful
>> > compatibility may be tricky.
>>
>> Are restrictive personality flags still a problem with user namespaces?
>> I think it would be fine to restrict this one to CAP_SYS_ADMIN.
>
> We could possibly get away with this, but now we're introducing a
> whole new mechanism. I'd rather just add proper per-namespace
> sysctls, but this is a pretty big hammer.
Oh, I wasn't aware of that. I thought that this already existed in some
form, e.g. prctl with PR_SET_SECCOMP requiring CAP_SYS_ADMIN unless
PR_SET_NO_NEW_PRIVS was active as well.
Thanks,
Florian
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