Messages in this thread |  | | Date | Mon, 07 May 2001 15:54:17 -0400 | From | Brian Gerst <> | Subject | Re: [PATCH] x86 page fault handler not interrupt safe |
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Linus Torvalds wrote: > > On Mon, 7 May 2001, Alan Cox wrote: > > > > That is nice. I hadn't thought about doing it that way. It still has the problem > > if %cr2 is corrupted by a vmalloc fault but it cleans up my other code paths > > nicely. > > See about "corruption" in previous email. It doesn't exist. > > For better debugging, we should probably walk the whole init_mm page table > tree when we take the fault, so this patch does that too: it > unconditionally copies the init_mm page table entries into the current > page table, while at the same time checking that they exist (including the > very last level that we didn't use to check at all). > > This means that if you access one page past a vmalloc'ed area, you will > get a nice oops instead of endless page faults that will fix up the page > tables with mappings that already exist.
This patch will still cause the user process to seg fault: The error code on the stack will not match the address in %cr2.
user fault (cr2=useraddr, error_code=5 or 7) interrupt vmalloc fault (cr2=vmallocaddr, error_code=0 or 2) handle vmalloc fault iret iret handle user fault (cr2=vmallocaddr, error_code=5 or 7)
We then fall down to find_vma() which will fail and then send SIGSEGV to the user process.
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