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Re: [PATCH 5/5] x86/ucode: Drop the match_reg[] field from AMD's microcode_patch
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 28 Oct 2024 14:18:48 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 28 Oct 2024 13:18:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.10.2024 15:22, Andrew Cooper wrote:
> This was true in the K10 days, but even back then the match registers were
> really payload data rather than header data.
>
> But, it's really model specific data, and these days typically part of the
> signature, so is random data for all intents and purposes.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> The single difference from this is:
>
> @@ -207587,7 +207587,7 @@
> ffff82d0402ad261: 4c 89 ce mov %r9,%rsi
> ffff82d0402ad264: 4c 39 c8 cmp %r9,%rax
> ffff82d0402ad267: 0f 82 c2 11 f6 ff jb ffff82d04020e42f
> <amd_ucode_parse.cold+0x55>
> -ffff82d0402ad26d: 41 83 f9 3f cmp $0x3f,%r9d
> +ffff82d0402ad26d: 41 83 f9 1f cmp $0x1f,%r9d
> ffff82d0402ad271: 0f 86 b8 11 f6 ff jbe ffff82d04020e42f
> <amd_ucode_parse.cold+0x55>
> ffff82d0402ad277: 85 ed test %ebp,%ebp
> ffff82d0402ad279: 75 55 jne ffff82d0402ad2d0
> <amd_ucode_parse+0x170>
>
> which is "mc->len < sizeof(struct microcode_patch)" expression in
> amd_ucode_parse().
Yet is it correct to effectively relax that check, i.e. to accept something
we previously would have rejected?
Jan
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