linux-kernel - Re: [PATCH v1] arm64/mm: Fix Boot panic on Ampere Altra

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMj1kXH=tPuM+irCsKgycUTbts8h9vD4m3tEtw51YFzWafdSUA@mail.gmail.com>
Date: Wed, 26 Feb 2025 07:59:04 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: Ryan Roberts <ryan.roberts@....com>, Catalin Marinas <catalin.marinas@....com>, 
	Mark Rutland <mark.rutland@....com>, Luiz Capitulino <luizcap@...hat.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] arm64/mm: Fix Boot panic on Ampere Altra

On Wed, 26 Feb 2025 at 01:10, Will Deacon <will@...nel.org> wrote:
>
> On Tue, Feb 25, 2025 at 07:05:35PM +0100, Ard Biesheuvel wrote:
> > Apologies for the breakage, and thanks for the fix.
> >
> > I have to admit that I was a bit overzealous here: there is no point
> > yet in using the sanitised value, given that we don't actually
> > override the PA range in the first place. This is something I've
> > prototyped for Android use, so that linear map randomization can be
> > force enabled on CPUs with a wide PArange, but right now, mainline
> > does not have that capability, and so I'd be inclined to just revert
> > the hunk that introduces the call to read_sanitised_ftr_reg() into
> > arm64_memblock_init(), especially given the fact that commit
> > 62cffa496aac was tagged for stable, and was already pulled into 6.13
> > and 6.12
> >
> > In any case, it would be good if we could get a fix into Linus's tree asap
>
> Makes sense. So the patch below?
>

Yes, but please don't forget the cc:stable

To the patch below,

Acked-by: Ard Biesheuvel <ardb@...nel.org>


> --->8
>
> From b76ddd40dd6fe350727a4b2ec50709fd919d8408 Mon Sep 17 00:00:00 2001
> From: Ryan Roberts <ryan.roberts@....com>
> Date: Tue, 25 Feb 2025 11:46:36 +0000
> Subject: [PATCH] arm64/mm: Fix Boot panic on Ampere Altra
>
> When the range of present physical memory is sufficiently small enough
> and the reserved address space for the linear map is sufficiently large
> enough, The linear map base address is randomized in
> arm64_memblock_init().
>
> Prior to commit 62cffa496aac ("arm64/mm: Override PARange for !LPA2 and
> use it consistently"), we decided if the sizes were suitable with the
> help of the raw mmfr0.parange. But the commit changed this to use the
> sanitized version instead. But the function runs before the register has
> been sanitized so this returns 0, interpreted as a parange of 32 bits.
> Some fun wrapping occurs and the logic concludes that there is enough
> room to randomize the linear map base address, when really there isn't.
> So the top of the linear map ends up outside the reserved address space.
>
> Since the PA range cannot be overridden in the first place, restore the
> mmfr0 reading logic to its state prior to 62cffa496aac, where the raw
> register value is used.
>
> Reported-by: Luiz Capitulino <luizcap@...hat.com>
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Closes: https://lore.kernel.org/all/a3d9acbe-07c2-43b6-9ba9-a7585f770e83@redhat.com/
> Fixes: 62cffa496aac ("arm64/mm: Override PARange for !LPA2 and use it consistently")
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> Link: https://lore.kernel.org/r/20250225114638.2038006-1-ryan.roberts@arm.com
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  arch/arm64/mm/init.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 9c0b8d9558fc..ccdef53872a0 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -279,12 +279,7 @@ void __init arm64_memblock_init(void)
>
>         if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
>                 extern u16 memstart_offset_seed;
> -
> -               /*
> -                * Use the sanitised version of id_aa64mmfr0_el1 so that linear
> -                * map randomization can be enabled by shrinking the IPA space.
> -                */
> -               u64 mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
> +               u64 mmfr0 = read_cpuid(ID_AA64MMFR0_EL1);
>                 int parange = cpuid_feature_extract_unsigned_field(
>                                         mmfr0, ID_AA64MMFR0_EL1_PARANGE_SHIFT);
>                 s64 range = linear_region_size -
> --
> 2.48.1.658.g4767266eb4-goog
>