linux-kernel - Re: [PATCH hotfix 6.12 v2 4/8] mm: resolve faulty mmap

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Message-ID: <CAHk-=whpXVBNvd0NJpw9=FGcuTuThwtfcKeM3Ug=Uk6kpChCPA@mail.gmail.com>
Date: Mon, 28 Oct 2024 10:22:32 -1000
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Mark Brown <broonie@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	Peter Xu <peterx@...hat.com>, linux-arm-kernel@...ts.infradead.org, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Aishwarya TCV <Aishwarya.TCV@....com>
Subject: Re: [PATCH hotfix 6.12 v2 4/8] mm: resolve faulty mmap_region() error
 path behaviour

On Mon, 28 Oct 2024 at 10:18, Lorenzo Stoakes
<lorenzo.stoakes@...cle.com> wrote:
>
> I'm genuinely not opposed to a horrible, awful:
>
> #ifdef CONFIG_ARM64
>         if (file && file->f_ops == shmem_file_operations)
>                 vm_flags |= VM_MTE_ALLOWED;
> #endif
>
> Early in the operation prior to the arch_validate_flags() check.

I would just put it inside the arm64 code itself.

IOW, get rid of the VM_MTE_ALLOWED flag entirely, and just make the
arm64 arch_validate_flags() code do something like

        if (flags & VM_MTE) {
                if (file->f_ops != shmem_file_operations)
                        return false;
        }

and be done with it.

Considering that we only have that horrendous arch_validate_flags()
for two architectures, and that they both just have magical special
cases for MTE-like behavior, I do think that just making it be a hack
inside those functions is the way to go.

              Linus