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Subject: Re: [RFC PATCH 1/3] mm: Introduce VM_IBT for CET legacy code bitmap
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <20190628194158.2431-1-yu-cheng.yu@intel.com>
Date:   Fri, 28 Jun 2019 14:49:32 -0700
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To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
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> On Jun 28, 2019, at 12:41 PM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>=20
> The previous discussion of the IBT legacy code bitmap is here:
>=20
>    https://lkml.org/lkml/2019/6/6/1032
>=20
> 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.
>=20
> This patch introduces VM_IBT for the bitmap.

There=E2=80=99s no need to allocate a bit for this and to clutter up the fau=
lt code with special cases. Use _install_special_mapping(), please.  If you n=
eed to make it more flexible to cover your use case, please do so.