Messages in this thread | | | Date | Mon, 14 Jul 2008 17:12:47 +0200 | From | Ingo Molnar <> | Subject | Re: [git pull] core, x86: make LIST_POISON less deadly |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Mon, 14 Jul 2008, Ingo Molnar wrote: > > > > +config ILLEGAL_POINTER_VALUE > > + hex > > + default 0 if X86_32 > > + default 0xffffc10000000000 if X86_64 > > This looks like a singularly bad pointer value on x86-64. > > Why not pick something that is *guaranteed* to fault? The above looks > like any future setup that supports 41 bits of addressing and has > extended the page tables (yes, it will happen eventually) will find > that to be a perfectly valid address? > > It's also visually confusing, since it's visually very close to a real > kernel pointer too. > > Grr. > > Why not use something sane like 0xdead000000000000, which has the high > bit set but very fundamentally isn't a valid pointer, and never will > be? And which is a *lot* more visually obvious too!
initially i suggested that too - but such addresses raise a #GP instead of a page fault so their decoding is a bit harder.
We dont do any instruction decoding in #GP handlers to figure out what happened, while in the pagefault case we know which address faulted, etc.
Perhaps we could try to make #GP handlers a bit more informative - although decoding instructions will make things a bit more fragile inevitably.
Perhaps make it 0xffffcdead0000000 ?
in any case, please ignore this topic until it's all worked out - no other topics depend on this one so it can be skipped safely.
Ingo
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