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Date: Tue, 6 Nov 2018 22:04:03 +0000
From: Will Deacon <will.deacon@....com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, keescook@...omium.org,
kernel-hardening@...ts.openwall.com, labbott@...hat.com,
jannh@...gle.com, mark.rutland@....com, james.morse@....com,
catalin.marinas@....com
Subject: Re: [PATCH v3 1/2] arm64: mm: purge lazily unmapped vm regions
before changing permissions
On Tue, Nov 06, 2018 at 10:44:03PM +0100, Ard Biesheuvel wrote:
> Call vm_unmap_aliases() every time we apply any changes to permission
> attributes of mappings in the vmalloc region. This avoids any potential
> issues resulting from lingering writable or executable aliases of
> mappings that should be read-only or non-executable, respectively.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
> arch/arm64/mm/pageattr.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index a56359373d8b..f8cf5bc1d1f8 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -93,6 +93,12 @@ static int change_memory_common(unsigned long addr, int numpages,
> if (!numpages)
> return 0;
>
> + /*
> + * Get rid of potentially aliasing lazily unmapped vm areas that may
> + * have permissions set that deviate from the ones we are setting here.
> + */
> + vm_unmap_aliases();
So this might_sleep(), which I don't think is currently the case for our
set_memory_XX() functions. However, a quick look at the existing callsites
indicates that's ok and matches the x86 implementation, so:
Acked-by: Will Deacon <will.deacon@....com>
Will
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