On Thu, Sep 3, 2015 at 10:19 AM, Stas Sergeev <[email protected]> wrote: > 03.09.2015 19:57, Linus Torvalds пишет: >> On Thu, Sep 3, 2015 at 8:44 AM, Austin S Hemmelgarn >> <[email protected]> wrote: >>> >>> This lets you turn this on or off at runtime. >> >> Tangential aside: we already effectively have a flag that could turn >> off vm86 mode dynamically: /proc/sys/vm/mmap_min_addr. >> >> Sadly (or not) we default it to 4096, which still leaves vm86 mode >> usable, although it effectively disables *dos* use for it. Which is >> kind of the worst of both worlds: you can use the vm86() system call >> for bad things (if you can find a hole in it), but you probably cannot >> actually use it for DOS emulation, because the traditional BIOS data >> segment is at 0040. >> >> Anyway, what that means is that pretty much the only *valid* use of >> vm86() mode is probably when the system maintainer has set >> 'mmap_min_addr' to zero. So we could probably use that as an already >> existing flag that disallows vm86 by our current default values. >> >> Stas - can you confirm that to actually use vm86 mode, you end up >> setting that mmap_min_addr thing to zero? Or do you end up using a >> mixed-mode setup, where you use vm86() for most things, but emulate >> things that trap in the zero page? > Yes, good point. > dosemu complains about /proc/sys/vm/mmap_min_addr. > Trapping on zero-page access will likely not work, because > IIRC some distros raise that value even more. > So yes, please use that to completely disable vm86(). > You won't even break dosemu's checks, because it (obviously) > tries mmap() before trying vm86(). >
I'm okay with that. Shall I send a patch? There's also vbetool, but I think that almost everyone considers it dead at this point, and it seems reasonably likely that it needs mmap_min_addr == 0 as well. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
