linux-kernel - Re: [PATCH v2 11/25] x86/sev: Adjust directmap to avoid inadvertant RMP faults

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Message-ID: <20240127114207.GBZbTsDyC3hFq8pQ3D@fat_crate.local>
Date: Sat, 27 Jan 2024 12:42:07 +0100
From: Borislav Petkov <bp@...en8.de>
To: Michael Roth <michael.roth@....com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
	linux-mm@...ck.org, linux-crypto@...r.kernel.org,
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	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
	pankaj.gupta@....com, liam.merwick@...cle.com
Subject: Re: [PATCH v2 11/25] x86/sev: Adjust directmap to avoid inadvertant
 RMP faults

On Fri, Jan 26, 2024 at 05:54:20PM -0600, Michael Roth wrote:
> Is something like this close to what you're thinking? I've re-tested with
> SNP guests and it seems to work as expected.
> 
> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index 846e9e53dff0..c09497487c08 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -421,7 +421,12 @@ static int adjust_direct_map(u64 pfn, int rmp_level)
>         if (WARN_ON_ONCE(rmp_level > PG_LEVEL_2M))
>                 return -EINVAL;
> 
> -       if (WARN_ON_ONCE(rmp_level == PG_LEVEL_2M && !IS_ALIGNED(pfn, PTRS_PER_PMD)))
> +       if (!pfn_valid(pfn))

_text at VA 0xffffffff81000000 is also a valid pfn so no, this is not
enough.

Either this function should not have "direct map" in the name as it
converts *any* valid pfn not just the direct map ones or it should check
whether the pfn belongs to the direct map range.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette