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List:       linux-doc
Subject:    Re: [RFC PATCH 1/3] mm: Introduce VM_IBT for CET legacy code bitmap
From:       Andy Lutomirski <luto () amacapital ! net>
Date:       2019-06-28 21:49:32
Message-ID: CBB8C19E-7F65-4D43-9783-6383478700A1 () amacapital ! net
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> On Jun 28, 2019, at 12:41 PM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> 
> The previous discussion of the IBT legacy code bitmap is here:
> 
> https://lkml.org/lkml/2019/6/6/1032
> 
> When CET Indirect Branch Tracking (IBT) is enabled, the processor expects
> every branch target is an ENDBR instruction, or the target's address is
> marked as legacy in the legacy code bitmap.  The bitmap covers the whole
> user-mode address space (TASK_SIZE_MAX for 64-bit, TASK_SIZE for IA32),
> and each bit represents one page of linear address range.
> 
> This patch introduces VM_IBT for the bitmap.

There's no need to allocate a bit for this and to clutter up the fault code with \
special cases. Use _install_special_mapping(), please.  If you need to make it more \
flexible to cover your use case, please do so.


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