Messages in this thread | ![/](/images/icornerl.gif) | | From | "Riley Williams" <> | Subject | Re: [BUG] FIXMAP-related change to mm/memory.c | Date | Fri, 13 Jun 2003 08:28:47 +0100 |
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Hi Linus, all.
>> Is it possible to constrain the FIXADDR range on x86/x86-64 >> (FIXADDR_START-FIXADDR_TOP) such that the entire range is >> read-only by user-level? If so, we could simplify the >> permission test like this:
> Well, you could replace the uses of FIXADDR_START/FIXADDR_TOP > with something like FIXADDR_USER_START/FIXADDR_USER_TOP, and > then force those to cover only the _one_ user-accessible page. > > Something like > > #define FIXADDR_USER_START (fix_to_virt(FIX_VSYSCALL)) > #define FIXADDR_USER_END (FIXADDR_USER_START + PAGE_SIZE) > > should work. In that case you can drop the page table testing, > since we "know" it is safe.
Should FIXADDR_USER_END point to the last byte of the relevant page, or to the first byte of the following page as per Linus's suggestion? The above looks like an off-by-one bug to me?
Best wishes from Riley. --- * Nothing as pretty as a smile, nothing as ugly as a frown.
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