linux-kernel - Re: [PATCH AUTOSEL 5.19 05/58] arm64: kernel: drop unnecessary PoC cache clean+invalidate

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Date:   Mon, 8 Aug 2022 11:05:29 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Will Deacon <will@...nel.org>, catalin.marinas@....com,
        bp@...e.de, Jason@...c4.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 5.19 05/58] arm64: kernel: drop unnecessary PoC
 cache clean+invalidate

On Mon, 8 Aug 2022 at 03:31, Sasha Levin <sashal@...nel.org> wrote:
>
> From: Ard Biesheuvel <ardb@...nel.org>
>
> [ Upstream commit 2e945851e26836c0f2d34be3763ddf55870e49fe ]
>
> Some early boot code runs before the virtual placement of the kernel is
> finalized, and we used to go back to the very start and recreate the ID
> map along with the page tables describing the virtual kernel mapping,
> and this involved setting some global variables with the caches off.
>
> In order to ensure that global state created by the KASLR code is not
> corrupted by the cache invalidation that occurs in that case, we needed
> to clean those global variables to the PoC explicitly.
>
> This is no longer needed now that the ID map is created only once (and
> the associated global variable updates are no longer repeated). So drop
> the cache maintenance that is no longer necessary.
>
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
> Link: https://lore.kernel.org/r/20220624150651.1358849-9-ardb@kernel.org
> Signed-off-by: Will Deacon <will@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

NAK

This patch *must* *not* be backported. It will break the boot.

And again, *please* stop spamming people with broken backports like this.

Can you explain why it is justified to use a bot to generate hundreds
of patches, and leave it to overloaded maintainers to spot the ones
that are broken? Is it because your time is more valuable than mine?

I have already asked (and you have already agreed) to disregard all
patches authored by me from this broken-by-design process. But here we
are, with yet another set of broken patches queued up all the way back
to v5.15.

So please, don't use AUTOSEL on *any* patch that was authored by me. I
understand the concept of a -stable kernel. I known what cc:stable
means. I know that a fixes: tag means. I don't need help from your
bot, it is only causing grief.

Thanks,
Ard.


> ---
>  arch/arm64/kernel/kaslr.c | 11 -----------
>  1 file changed, 11 deletions(-)
>
> diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
> index 418b2bba1521..d5542666182f 100644
> --- a/arch/arm64/kernel/kaslr.c
> +++ b/arch/arm64/kernel/kaslr.c
> @@ -13,7 +13,6 @@
>  #include <linux/pgtable.h>
>  #include <linux/random.h>
>
> -#include <asm/cacheflush.h>
>  #include <asm/fixmap.h>
>  #include <asm/kernel-pgtable.h>
>  #include <asm/memory.h>
> @@ -72,9 +71,6 @@ u64 __init kaslr_early_init(void)
>          * we end up running with module randomization disabled.
>          */
>         module_alloc_base = (u64)_etext - MODULES_VSIZE;
> -       dcache_clean_inval_poc((unsigned long)&module_alloc_base,
> -                           (unsigned long)&module_alloc_base +
> -                                   sizeof(module_alloc_base));
>
>         /*
>          * Try to map the FDT early. If this fails, we simply bail,
> @@ -174,13 +170,6 @@ u64 __init kaslr_early_init(void)
>         module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
>         module_alloc_base &= PAGE_MASK;
>
> -       dcache_clean_inval_poc((unsigned long)&module_alloc_base,
> -                           (unsigned long)&module_alloc_base +
> -                                   sizeof(module_alloc_base));
> -       dcache_clean_inval_poc((unsigned long)&memstart_offset_seed,
> -                           (unsigned long)&memstart_offset_seed +
> -                                   sizeof(memstart_offset_seed));
> -
>         return offset;
>  }
>
> --
> 2.35.1
>