Messages in this thread | | | Subject | Re: [PATCH 0/9] Kconfig symbol clean-up on ./arch/x86/ | From | Dave Hansen <> | Date | Tue, 3 Aug 2021 07:32:39 -0700 |
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On 8/3/21 4:35 AM, Lukas Bulwahn wrote: > - a reference to STRICT_IOMEM in arch/x86/mm/init.c > unclear to me: which exact config this refers to
Are you referring to the reference in this comment?
> + /* > + * This must follow RAM test, since System RAM is considered a > + * restricted resource under CONFIG_STRICT_IOMEM. > + */ > + if (iomem_is_exclusive(pagenr << PAGE_SHIFT)) { > + /* Low 1MB bypasses iomem restrictions. */ > + if (pagenr < 256) > + return 1; ...
That came from here:
> commit a4866aa812518ed1a37d8ea0c881dc946409de94 > Author: Kees Cook <keescook@chromium.org> > Date: Wed Apr 5 09:39:08 2017 -0700 > > mm: Tighten x86 /dev/mem with zeroing reads
Which also added this hunk:
> #ifdef CONFIG_STRICT_DEVMEM > +static inline int page_is_allowed(unsigned long pfn) > +{ > + return devmem_is_allowed(pfn); > +}
and talks about CONFIG_STRICT_DEVMEM in the changelog:
> mm: Tighten x86 /dev/mem with zeroing reads > > Under CONFIG_STRICT_DEVMEM, reading System RAM through /dev/mem is > disallowed. However, on x86, the first 1MB was always allowed for BIOS ...
It's a pretty safe guess that STRICT_IOMEM refers to CONFIG_STRICT_DEVMEM.
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