From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH mm-unstable v1 20/20] mm: rename FOLL_FORCE to FOLL_PTRACE
Date: Thu, 17 Nov 2022 16:31:24 -0800
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, etnaviv@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Jason Gunthorpe <jgg@ziepe.ca>, John Hubbard <jhubbard@nvidia.com>, Peter Xu <peterx@redhat.com>, Greg Kroah-Hartman <gregkh>

On Thu, Nov 17, 2022 at 03:20:01PM -0800, Linus Torvalds wrote:
> On Thu, Nov 17, 2022 at 2:58 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > Oh, er, why does get_arg_page() even need FOLL_FORCE? This is writing the
> > new stack contents to the nascent brpm->vma, which was newly allocated
> > with VM_STACK_FLAGS, which an arch can override, but they all appear to include
> > VM_WRITE | VM_MAYWRITE.
> 
> Yeah, it does seem entirely superfluous.
> 
> It's been there since the very beginning (although in that original
> commit b6a2fea39318 it was there as a '1' to the 'force' argument to
> get_user_pages()).
> 
> I *think* it can be just removed. But as long as it exists, it should
> most definitely not be renamed to FOLL_PTRACE.
> 
> There's a slight worry that it currently hides some other setup issue
> that makes it matter, since it's been that way so long, but I can't
> see what it is.

My test system boots happily with it removed. I'll throw it into -next
and see if anything melts...

-- 
Kees Cook