Re: [BUG] FIXMAP-related change to mm/memory.c

["Riley Williams" <Riley@Williams.Name>]

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.

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.488 / Virus Database: 287 - Release Date: 5-Jun-2003