From: Catalin Marinas <catalin.marinas@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Pingfan Liu <kernelfans@gmail.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Will Deacon <will@kernel.org>,
Pasha Tatashin <pasha.tatashin@soleen.com>,
James Morse <james.morse@arm.com>,
Matthias Brugger <mbrugger@suse.com>
Subject: Re: [PATCH] arm64: mm: assign PXN permission in trans_pgd
Date: Thu, 11 Nov 2021 18:18:17 +0000 [thread overview]
Message-ID: <YY1eacUqllp9S+6A@arm.com> (raw)
In-Reply-To: <CAMj1kXEnzTYvEugk33KCPfPty4JW4SMaY_8sSwvJN=-SvX9sTQ@mail.gmail.com>
On Thu, Nov 11, 2021 at 05:13:02PM +0100, Ard Biesheuvel wrote:
> On Thu, 11 Nov 2021 at 17:09, Catalin Marinas <catalin.marinas@arm.com> wrote:
> > On Thu, Nov 11, 2021 at 02:03:16PM +0800, Pingfan Liu wrote:
> > > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
> > > index d7da8ca40d2e..7b43d179e94d 100644
> > > --- a/arch/arm64/mm/trans_pgd.c
> > > +++ b/arch/arm64/mm/trans_pgd.c
> > > @@ -67,7 +67,7 @@ static int copy_pte(struct trans_pgd_info *info, pmd_t *dst_pmdp,
> > > dst_ptep = trans_alloc(info);
> > > if (!dst_ptep)
> > > return -ENOMEM;
> > > - pmd_populate_kernel(NULL, dst_pmdp, dst_ptep);
> > > + pmd_populate_kernel(&init_mm, dst_pmdp, dst_ptep);
> > > dst_ptep = pte_offset_kernel(dst_pmdp, start);
> >
> > Commit 5de59884ac0e ("arm64: trans_pgd: pass NULL instead of init_mm to
> > *_populate functions") actually replaced &init_mm with NULL. Commit
> > 59511cfd08f3 ("arm64: mm: use XN table mapping attributes for
> > user/kernel mappings") introduced the VM_BUG_ON.
> >
> > So we either revert Pasha's trans_pgd commit (as per your patch) or we
> > fix Ard's commit to make it aware of a NULL mm and either skip the table
> > UXN altogether or treat it as init_mm.
> >
>
> That code in pmd_populate_kernel() does not actually *use* the mm
> argument at all, it just BUGs if its value != init_mm. So we can just
> relax the BUG() to disregard mm == NULL.
We also have pud_populate() that ends up setting PUD_TABLE_PXN when mm
is NULL. Fortunately we don't execute anything from those mappings, they
are just a copy of the linear map.
BTW, in line with PAGE_KERNEL, pud_populate() could set both UXN and PXN
for init_mm mappings.
--
Catalin
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next prev parent reply other threads:[~2021-11-11 18:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 6:03 [PATCH] arm64: mm: assign PXN permission in trans_pgd Pingfan Liu
2021-11-11 16:09 ` Catalin Marinas
2021-11-11 16:13 ` Ard Biesheuvel
2021-11-11 18:18 ` Catalin Marinas [this message]
2021-11-11 18:24 ` Catalin Marinas
2021-11-12 5:18 ` Pingfan Liu
2021-11-12 5:22 ` [PATCHv2] arm64: mm: Fix VM_BUG_ON(mm != &init_mm) for trans_pgd Pingfan Liu
2021-11-12 14:26 ` Catalin Marinas
2021-11-12 14:37 ` Pasha Tatashin
2021-11-16 10:39 ` Will Deacon
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