linux-kernel - Re: [PATCH 4.9 086/104] arm64: kasan: avoid bad virt_to

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Date:   Fri, 6 Oct 2017 19:13:22 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Laura Abbott <labbott@...hat.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: Re: [PATCH 4.9 086/104] arm64: kasan: avoid bad virt_to_pfn()

Hi Greg,

On Fri, Oct 06, 2017 at 10:52:04AM +0200, Greg Kroah-Hartman wrote:
> 4.9-stable review patch.  If anyone has any objections, please let me know.

I'm a little confused as to why this is being backported, given it
wasn't Cc'd stable or marked as a fix.

The lm_alias() helper was only introduced in v4.10, and I don't recall
seeing that backported.

What's going on here?

Thanks,
Mark.

> 
> ------------------
> 
> From: Mark Rutland <mark.rutland@....com>
> 
> 
> [ Upstream commit b0de0ccc8b9edd8846828e0ecdc35deacdf186b0 ]
> 
> Booting a v4.11-rc1 kernel with DEBUG_VIRTUAL and KASAN enabled produces
> the following splat (trimmed for brevity):
> 
> [    0.000000] virt_to_phys used for non-linear address: ffff200008080000 (0xffff200008080000)
> [    0.000000] WARNING: CPU: 0 PID: 0 at arch/arm64/mm/physaddr.c:14 __virt_to_phys+0x48/0x70
> [    0.000000] PC is at __virt_to_phys+0x48/0x70
> [    0.000000] LR is at __virt_to_phys+0x48/0x70
> [    0.000000] Call trace:
> [    0.000000] [<ffff2000080b1ac0>] __virt_to_phys+0x48/0x70
> [    0.000000] [<ffff20000a03b86c>] kasan_init+0x1c0/0x498
> [    0.000000] [<ffff20000a034018>] setup_arch+0x2fc/0x948
> [    0.000000] [<ffff20000a030c68>] start_kernel+0xb8/0x570
> [    0.000000] [<ffff20000a0301e8>] __primary_switched+0x6c/0x74
> 
> This is because we use virt_to_pfn() on a kernel image address when
> trying to figure out its nid, so that we can allocate its shadow from
> the same node.
> 
> As with other recent changes, this patch uses lm_alias() to solve this.
> 
> We could instead use NUMA_NO_NODE, as x86 does for all shadow
> allocations, though we'll likely want the "real" memory shadow to be
> backed from its corresponding nid anyway, so we may as well be
> consistent and find the nid for the image shadow.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Acked-by: Laura Abbott <labbott@...hat.com>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  arch/arm64/mm/kasan_init.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -153,7 +153,7 @@ void __init kasan_init(void)
>  	clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);
>  
>  	vmemmap_populate(kimg_shadow_start, kimg_shadow_end,
> -			 pfn_to_nid(virt_to_pfn(_text)));
> +			 pfn_to_nid(virt_to_pfn(lm_alias(_text))));
>  
>  	/*
>  	 * vmemmap_populate() has populated the shadow region that covers the
> 
>